Transition from Magmatic to Phreatomagmatic Eruptions in Young Ciremai Volcano, Indonesia: Insights from Stratigraphy, Componentry, and Textural Analysis of Tephra Deposits

Transition from Magmatic to Phreatomagmatic Eruptions in Young Ciremai Volcano, Indonesia: Insights from Stratigraphy, Componentry, and Textural Analysis of Tephra Deposits | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Transition from Magmatic to Phreatomagmatic Eruptions in Young Ciremai Volcano, Indonesia: Insights from Stratigraphy, Componentry, and Textural Analysis of Tephra Deposits Wildan Nur Hamzah, Tsukasa Ohba, Muhammad Andriansyah Gurusinga, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5017130/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Feb, 2025 Read the published version in Earth, Planets and Space → Version 1 posted 5 You are reading this latest preprint version Abstract Vulcanian eruptions, characterized by intermediate magma compositions, pose significant hazards due to their potential for both magmatic and phreatomagmatic fragmentation. The Young Ciremai volcano located in Indonesia has undergone recent phreatic-phreatomagmatic eruptions (from 1698 to 1951), with previous eruptions likely exhibiting both magmatic and phreatomagmatic fragmentations. In order to reconstruct the eruptive histories and elucidate the fragmentation mechanism, we integrate stratigraphic analysis, grain size distribution, componentry, bulk XRD analysis of fine ash, and petrographic analysis, which encompassed the morphometry, vesicularity, and crystallinity of ash particles. The results indicate a complex eruption history characterized by changing fragmentation mechanisms. Magmatic fragmentation correlates with the Vulcanian eruption style, which is characterized by diverse grain size distributions and higher vesicle number densities. The interactions between magma and water drive phreatomagmatic fragmentation, characterized by predominant finer ash exhibiting blocky textures and lower vesicle number densities. The eruptive evolution is described into three distinct stages: Stage 1 indicates magmatic fragmentation resulting from conduit plugging, Stage 2 signifies phreatomagmatic activity originating from the interaction with shallow groundwater, and Stage 3 emphasizes phreatic-hydrothermal activity with continuous recent solfatara manifestation. The results highlight the potential hazards of alternating magmatic and phreatomagmatic eruptions, including pyroclastic density currents and sudden phreatic explosions. Vulcanian Phreatomagmatic Stratigraphy Componentry Young Ciremai volcano. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 1. Introduction Vulcanian eruptions are typically associated with magmas of intermediate compositions, such as basaltic andesite, andesite, and evolved dacitic magmas (e.g., Mercalli and Silvestri, 1891; Cas and Wright, 1987; Lockwood and Hazlett, 2010; Clarke et al., 2015; De Silva and Lindsay, 2015; Belousov et al., 2021). The eruptive style, first described by Mercalli and Silvestri (1891) based on observations at Mt. Vulcano in the Aeolian Islands, is characterized by small to moderate, short-lived explosions spanning from seconds to minutes. These explosions generate dark-gray, ash-laden eruption clouds that rise several kilometers into the atmosphere (e.g., Cas and Wright, 1987; Lockwood and Hazlett, 2010; Clarke et al., 2015; Belousov et al., 2021). Ballistic fragments, such as dense volcanic bombs, often eject during these events, followed by intense shock waves due to the rapid decompression (e.g., Cas and Wright, 1987; Lockwood and Hazlett, 2010; Clarke et al., 2015; Belousov et al., 2021). The evolution of volcanic edifices and structures can promote the formation of groundwater or hydrothermal systems, which consequently influences eruption dynamics. The interaction between magma and external water contributes to the complexity and variability in fragmentation mechanisms, categorizing eruptions as magmatic, phreatomagmatic, phreatic, or hydrothermal (e.g., Németh and Kósik, 2020; Montanaro et al., 2022). Young Ciremai in Indonesia has experienced phreatic-phreatomagmatic eruptions recently, notably in the years 1951, 1937-1938, 1775, 1772, and 1698 (Kusumadinata, 1979; Newhall and Dzurisin, 1988; Volcanological Survey of Indonesia, 2024; Global Volcanism Program, 2024). The eruption's distribution was defined as phreatomagmatic deposits on the geological map from the volcanological survey of Indonesia (Situmorang et al. 1995). The geological maps indicate that the eruptive history deposits prior to 1698 might be related to both fragmentation mechanisms, either magmatic or phreatomagmatic. Identification of these fragmentation mechanisms from the tephra deposits is essential for understanding the long-term evolution of conduit structure from magmatic to phreatomagmatic Vulcanian fragmentation in the Young Ciremai volcano. The objectives of this study are: 1) to elucidate the mechanisms of fragmentation and their key features through stratigraphy, grain size distribution, component analysis, bulk XRD analyses of fine ash particles, and petrographic and morphological study of ash particles; 2) to clarify the vesiculation processes of magma within the conduit during pre- and syn-fragmentation through quantitative petrographic analysis, including vesicle size distribution (VSD), vesicle number density (VND), bulk vesicularity, and bulk crystallinity; 3) to examine the evolution of conduit structure from magmatic to phreatomagmatic eruptions through temporal analysis of eruptive history as determined by stratigraphy; and 4) to determine the variability of potential hazards impacting approximately four million residents in nearby to CVC, estimated from Majalengka and Kuningan within a 4-8 km radius (BPS-Statistics Indonesia, 2024). Also, the findings aim to improve long-term volcano monitoring and risk assessment, especially for low-frequency eruptive events with limited data, as exemplified by the Young Ciremai volcano. 2. Overview of Ciremai Volcanic Complex The Ciremai Volcanic Complex (CVC) is situated in the Java Trench (Figure 1a), a major tectonic feature formed by the convergence of the Indo-Australian and Eurasian plates in this region of Indonesia (e.g., Hamilton, 1979; Newhall and Dzurisin, 1988; Sendjadja et al., 2009; Setijadji, 2010; Bear-Crozier et al., 2016). Located on the border of Kuningan and Majalengka Regencies in West Java, Indonesia, the CVC comprises three main edifices: Putri, Gegerhalang, and Young Ciremai (Situmorang et al., 1995). The geological map of CVC by Situmorang et al. (1995) in Figure 1c delineates four periods of volcanic activity. The oldest Putri period is characterized by dissected morphology in the south flank and the porphyritic andesitic lava extrusion. The subsequent Gegerhalang period (>40,800 years BP) constructed a horseshoe-shaped rim structure coincident with a northward migration of the eruptive vent, forming rough topography (Newhall and Dzurisin, 1988; Situmorang et al., 1995). Renewed eruptive activity during the Ciremai-I (13,350 years BP) period contributed to the growth of the Young Ciremai stratovolcano edifice (illustrated in Figure 1c). The Young Ciremai andesitic lava flow (Cl1 sample) contains plagioclase, pyroxenes, and opaque phenocrysts. The explosive eruption deposits include one pyroclastic fallout deposit (Cpfa1) and two pyroclastic flow deposits (Cpfl1 and Cpfl2) (Situmorang et al., 1995). Cpfa1 consists of a well-stratified tephra sequence consisting of pumice (1-5 cm), scoria, and lithic clasts, well exposed in the Argalingga area (Situmorang et al., 1995). Cpfl1 is a pyroclastic flow deposit with vertical facies change; the lower 30 m is unwelded, and the upper 6 m is welded volcanic breccia. The deposit consists of pumice and lithic clasts in a grey-to-reddish ash matrix. On the other hand, Cpfl2 is a non-welded, 2- to 4-m-thick pyroclastic flow deposit. Cpfl2 was radiocarbon dated from a charcoal sample to 13,350 years BP (Situmorang et al., 1995). Ongoing eruptive activity during the Ciremai-II period (< 13,350 years) has continued to the present day. Basaltic-andesitic lava flows erupted from central vents (Cl1, Cl3, Cl4, while flank eruptions produced basaltic lavas (Bl, Dl, Pl, and Sl) eruptions. Two pyroclastic fall deposits (Cpfa2 and Cpfa3) were also emplaced during this youngest period. Cpfa2 deposit is well-exposed in the Tegalijamuju area, comprising stratified lapilli and ash layers that contain pumice, scoria, and lithic. Cpfa3 deposits exposed near the summit area are phreatomagmatic eruption products, comprising ash aggregates along with lithic and pumice clasts (Situmorang et al., 1995). Major elements analysis of lava from CVC classified its composition as basaltic andesite and andesite, with SiO 2 ranging from 53-58% (Sendjaja et al., 2009). The CVC lavas are typically high-alumina basalts (HABs), With elevated Al 2 O 3 (16.2 to 18.9 wt%), low MgO (3.2 to 6.7 wt%), and medium K 2 O (1.3 to 2.3 wt%). Modal mineralogy of the CVC lavas contains phenocrysts of plagioclase, pyroxene, olivine, and titanomagnetite (Hamzah et al., 2018; 2019). 3. Methods We identified 26 tephra outcrops from the Young Ciremai volcano along its western flank. Outcrops were distributed from the summit area to 5 km distance from the crater’s edge (Figure 1c). Individual tephra layers were carefully examined and correlated based on similarities in characteristics, including color, components, and soil boundaries (Lowe, 2011). Representative tephra samples were collected from three key localities – the summit area (Loc. 21) and two locations approximately 5 km from the crater (Loc. 1 and Loc. 2). The grain size distribution (GSD) of representative samples analysis was determined through dry sieving analysis of the 1ϕ intervals from -4 to 5ϕ. The key GSD parameters were calculated from the results: median grain size (Mdϕ), ash proportion (< -1ϕ), lapilli proportion, and cumulative weight percentages finer than 0ϕ (F1) and 4ϕ (F2) (See. Inman; 1952; Walker 1971; Miyabuchi et al., 2013). For component analysis, the 3-0ϕ size fractions (125µm - 1mm) were cleaned using an ultrasonic bath to remove any adhering material or coatings. Eight distinct component types (Table 1) were defined based on their color, shape, surface texture, luster, and transparency under a stereo microscope (Gaunt et al., 2016; Gomez-Arango et al., 2018; Thivet et al., 2022; Ohba et al., 2022; Benet et al., 2024). Component proportions were quantified by counting an average of 1000 grains within each of three sub-size fractions (3-2 ϕ, 2-1 ϕ, and 1-0ϕ). Petrographic thin sections were made of coarse ash grains (1–0 ϕ size fractions). This size range provides optimal visualization of the ash particle morphology and internal micro-textures (Comida et al., 2021). Thin sections were examined under a polarized light microscope and BSE microphotograph acquired by SEM JEOL JSM-IT300 LV at the Faculty of International Resource Sciences, Akita University. An accelerating voltage of 15 kV and a working distance of 15 mm were used for SEM-BSE observation. Vesicle and micro-phenocryst were observed at 100x magnification, while microlite textures were characterized at 1000x magnification. Vesicle shape was classified based on the visual assessment as, spherical, elongated, or coalesced, defined by Noguchi et al. (2006). Microlite morphologies were described using the terminology of Shea and Hammer (2013) for skeletal, swallowtail, and euhedral habits. Vesicles and crystal edges were manually digitized from the BSE micrograph using CorelDraw and were quantified using Image-J software. The bulk vesicularity (BV), vesicle-free crystallinity and vesicle number density (VND) was calculated by following the equation from Suhendro (2024). Where N Av is the number density of vesicles in the unit area and D V is the average vesicle size. Image analysis of ash particles was carried out to quantify 2D shape parameters related to fragmentation mechanism (Delino and La Volpe, 1996; Liu et al., 2015; Dürig et al., 2018; Nurfiani & Maisonneuve, 2018; Dürig et al., 2021; Comida et al., 2022; Thivet et al., 2022; Gurusinga et al., 2023). Ash particle images were imported into CorelDraw to outline particle perimeters manually. Traced boundaries were exported as black and white TIFF images. The PARTISAN script (Durig et al., 2018) in MATLAB was used to calculate the 2D shape parameters of convexity, solidity, and form factor (Delino and La Volpe, 1996; Liu et al., 2015). The fine ash fractions (<4 ϕ) were analyzed to identify the secondary mineral alteration assemblages present within tephra units from YCT. X-ray diffractometer (XRD) analysis was conducted on a Rigaku MultiFlex using CuKα radiation from 2 to 60 o 2θ at a scan rate of 0.25 o /min from 2 to 60 o (Imura et al., 2021) at the Faculty of International Resource Sciences, Akita University. Operating conditions of 30 kV acceleration voltage and 16 mA filament current were used for the analysis. The qualitative mineral identification was carried out using the PDXL2 database. In addition, selected grains representing altered components were examined using an energy-dispersive spectrometer (EDS) to quantitatively assess the presence of secondary mineral alteration phases. 4. Results 4.1. Stratigraphy and lithofacies of Young Ciremai Tephra (YCT) A total of 26 tephra outcrop localities were identified from the summit area to 5 km from the Young Ciremai volcano. Ten tephra deposits (Units A to J) were described below in stratigraphic order (Figure 2a). Units A, B, C, D, E, and G are widely distributed from the summit to a 5 km distance from the crater, while Units F, H, I, and J are concentrated near the crater. Unit A , as the oldest Unit, is exposedat locs 1 and 9 (Figure 2a), overlying a 30- cm thick pale-brown soil layer (Figure 2b). It consists of well-sorted, medium- to fine-grained ash with an average measured thickness of 10-12 cm, showing normal grading and subtle bioturbation. This Unit contains dark color particles, including scoria and dense rock fragments. Unit B shows well-stratified tephra deposits and exhibits two different sequences in two localities. At Loc.1, Unit B consists of five sub-layers, of which the lower part comprises medium-fine ash overlain by stratified coarse-fine ash (Figure 2c). The upper layers consist of pumiceous and scoriaceous coarse ash and lapilli. At Loc.9b, Unit B occurs as a single continuous gradational layer (Figure 2e). The lower part contains dark scoria and dense components, ranging from coarse ash to lapilli grain sizes. On the upper part, the facies transition to lighter pumiceous lapilli to medium-ash layer. Unit C is observed at Loc. 1 and 9, where it consists of four thin layers (C1–C4) separated by brown soil layers, with up to about 6 cm of the total thickness (Figure 2e). Each of the thin layers comprises a well-sorted, medium to fine ash, and subtle bioturbation features. Specifically, C1 and C2 layers are separated by a 2 cm soil layer, a 5 cm soil layer between C2 and C3, and a 5 cm soil layer between C3 and C4. This Unit is overlain by a prominent pale brown soil layer of 45-60 thickness. Dark scoria and dense fragments are present in Unit C. Unit D was identified at all outcrop localities, distributed within 5 km of the summit crater (Figure 2f-2i). The total thickness ranges from 20-40 cm in the 5 km distance and increases to 86 cm in proximal exposures near the crater. This Unit contains a basal layer of light brown to pale gray fine-grained ash (Figure 2f-g). It is overlaid by scoria and dense rock fragments layers with multiple alternating medium and fine-grained ash layers. Unit E is well distributed within a 5-kilometer radius of the crater (Figure 2f-2i). In the 5 km radii, the total thickness is approximately 15-20 cm, consisting of alternating medium-fine ash facies. This unit, which reaches up to 62 cm thick in the proximal region, primarily consists of lapilli-fine ash, characterized by abundant scoria and dense block fragments. At Loc. 15, Loc. 16, and Loc. 17, we find a massive layer with abundant blocks to lapilli size, set in a fine ash matrix, overlying the tephra falls of Unit E. At Locs. 8 and 12, the top of the layer exhibits undulation and subtle bioturbation, overlaid by a 10-15 cm soil layer that develops between units D and E. Unit F comprises 32 thin stratified layers with approximately 47 cm of total thickness, containing some layers with ash aggregates and diffused features (Figure 2j). The lowermost deposit is F1, a 3 cm massive coarse ash layer with a block sag structure. Overlying are alternating layers classified as F2 consisting of an alternation of thin medium-fine ash deposits. The uppermost is F3, which consists of a fine-grain layer. Unit G consists of three upward coarsening sub-units of approximately 40 cm total thickness (Figure 2k). Block sag structures were documented in fine ash layers throughout this Unit, which also contains ash aggregates and diffused layers (Figure 2m). The lower sub-unit (G1) comprises a set of medium-fine ash layers with 15 cm total thickness. The middle sub-unit (G2) is a coarse to fine ash layer set with 10 cm total thickness. The uppermost sub-unit (G3) consists of a set of lapilli-fine ash layers reaching 15 cm thickness. Unit H has an overall thickness of 60 cm divided into two defined sub-units containing abundant ash aggregates (Figure 2k-l). The lower sub-unit (H1) is a 25 cm thick medium-fine ash layer that exhibits a block sag structure. The upper sub-unit (H2) consists of alternating medium-fine ash layers reaching 35 cm thickness and displaying diffuse stratification (Figure 2l). This unit is overlain by a 3-5 cm dark brown soil layer, which separates between Units H and I. Unit I comprises a total thickness of approximately 23 cm consisting of two defined sub-units (Figure 2n-p). The lower sub-unit (I1) consists of a 9 cm thick fine ash layer with variations in colors: reddish, yellowish, and white-grey. The overlying upper sub-unit (I2) reaches 14 cm in thickness. It is characterized by a consolidated medium-fine ash layer that also contains ash aggregates. Unit J comprises the uppermost stratified sequence identified in YCT, reaching 30 cm in total thickness (Figure 2n-p). It consists of two sub-units. As the lower sub-unit (j1), has a thin fine ash layer pile. Overlying is a thicker sub-unit J2, characterized as a layer containing block and exhibiting block sag structures. Both sub-units range from yellowish to light color, which appear consolidated with dispersed ash aggregates. The ten tephra units of YCT can be classified into four lithofacies based on their lithological features: 1. Pumiceous fall (Pf lithofacies) – exemplified by pumice-rich clast Unit B. 2. Scoriaceous-blocky ash fall (Sf lithofacies) – occurred prominently in the lower-stratified Units A, C, D, and E. 3. Diffused stratification with ash aggregate (Ds-aa lithofacies) – comprised of Units F, G, and H, featured variable ash aggregate abundances. 4. Abundantly altered components with ash aggregate (Alt-aa lithofacies) – stratified the uppermost Units I and J contained an abundant proportion of secondary alteration products. 4.2. Geology of crater area The Young Ciremai volcanic edifice shows an elongated crater rim that includes two major craters: Crater-I and Crater-II. The upper diameters of the craters estimate approximately 500 m and 850 m, whereas the lower diameters are approximately 150 m and 300 m, respectively. The crater morphology shows a typical funnel shape, characterized by inner walls with slopes between 30° and 90° and depths of 100 to 150 m. The crater surfaces consist of unconsolidated debris, comprising mud and rockfall fragments resulting from wall collapses (Figure 3B). The walls of the crater are composed of massive lava flows (ML), thick lava flows (IL-1), tephra from Unit C, thin lava flows (IL-2), and tephra from Units D to J (Figure 3A). The angular contacts that differentiate Unit G from Unit H are distinctly obvious (Figure 3C). Active solfataras and hydrothermal manifestations are situated along the border zone between Crater-I and Crater-II (Figure 3E). 4.3. Grain size distributions (GSDs) Particle size analysis of YCT deposits indicates that they are predominant in ash-size components (<1 mm), constituting over 50% of the samples from all stratigraphic units (Supplementary 1). Most GSD histograms exhibit unimodal distributions (Figure 4a). In the crater area (Units D-J), two clusters of grain size were identified based on ash fraction and median particle size (Mdϕ) (Figure 4a). The first cluster (Units D-E) contained 50-60% of ash with Mdϕ ranges from 0 to 2ϕ. The second and larger cluster (Units F-J) is characterized by higher ash fractions (~80%) and finer Mdϕ ranges from 2 to 4ϕ. At 5 km from the crater (Units A-E), only Unit B comprises coarse ash and lapilli (maximum grain size -4ϕ). In contrast, the other Units, including Unit A, Unit C, Unit D, and Unit E, contained finer ash (maximum grain size -2ϕ; Figure 4b). Unit B consisted of 2ϕ. 4.4. Volcanic ash characteristics Ash particles in YCT deposits were classified into eight categories based on the visual attributes (Figure 5): light-colored vesicular ash (LV), black vesicular ash (BV), black dense ash (BD), gray dense ash (GD), partially-completely oxidized ash (Ox), altered ash (Alt), free crystal (FC), and ash aggregate (AA). These eight types were then grouped into two general categories: juvenile and non-juvenile components. The juvenile components included LV, BV, and BD clasts characterized by fresh surface textures, distinct mineral assemblages, and microlite textures. The non-juvenile components comprise GD, Ox, and Alt particles derived from external wall rock or older deposits reworked during eruptions. Table 1 summarizes the distinguishing characteristics of each ash category, with representative photomicrographs presented in Figure 4. LV ash particle exhibits fluidal to irregular shapes with a rough glossy surface. It has various colors from translucent to opaque in light-brown, pale-brown, and yellow-brown. Abundant vesicles are observed, varying from spherical to elongated shapes and coalesced forms. It contains microlites with 10-30 µm size and skeletal to swallowtail morphology. BV ash particles appear as black, glossy fluidal ash with a rough surface. The vesicle proportion is less than in LV ash but the vesicle shape tends to be more coalesced. Microlite sizes range from 1-10 µm with swallowtail morphology. BD ash particles appear as black, glossy surfaces and blocky shapes with sharp edges. It has a higher microlite proportion compared to LV and BV ash types, ranging from 1-10 µm with swallowtail morphology and 10-30 µm with euhedral texture. Fine nanolites (< 1 µm) of Fe-Ti oxides and mafic minerals also occur within interstices between microlites. GD ash particles appear dull, light grey to grey, blocky ash shape with sharp edges. Euhedral microlites are commonly found in this ash type. OX ash particles appear dull, blocky shapes with sharp or rounded edges, exhibiting varied colors of grey, orange, and reddish colors. Microlite textures resemble those in GD particles with altered plagioclase. ALT ash particles, found exclusively in Units I and J, display discoloration ranging from white, grey, pink, and pale yellow. The BSE imaging of ALT particles depicts dissolution and hydrothermal infill textures, indicative of secondary alteration processes more intensive than the GD and OX components. AA components comprise various types of ash aggregates. They were subdivided into four types (Figure 6) based on the morphological scheme of Brown et al. (2012): ash cluster (PC1), coated particles (PC2), poorly structured pellets (AP1), and pellets with concentric structure (AP2). PC1 and PC2 both exhibited irregular shapes, where PC1 comprised mixes of free crystal and lithic clast smaller than 100 µm (Figures 6g-i). PC2 featured lithic clast partly coated by fine ash less than <20 µm diameter (Figures 6a, b, d). AP1 shows massive, spherical to subspherical forms constructed of loosely packed free crystals smaller than 50 µm (Figures 6c-f). AP2 has spherical to subspherical morphologies containing a core of massive or poorly structured ash 5-10 µm in diameter surrounded by an outer rim of finer ash less than 5 µm diameter (Figure 6c). FC particles represent a single crystal of mostly clinopyroxene and plagioclase. Some FC grains contain glass with vesicles along the rims, while others show an uncoated surface with hackle marks. 4.5. Componentry Componentry analysis distinguished the YCT tephra deposits based on the occurrence and abundance of LV, AA, and ALT particles (Figure 7). The juvenile components of LV particles characterized the Pf and Sf lithofacies of Units A-E, while BV and BD particles occurred prominently across all lithofacies. AA particles dominated the Ds-aa and Alt-aa lithofacies, with only minor occurrences in Unit B5 of Pf lithofacies. Significant proportions of secondary ALT particles typified the Alt-aa lithofacies stratified as uppermost Units I-J. 4.6. Altered components compositions Mineral assemblages in fine ash particles and altered components were characterized using bulk XRD and SEM-EDS methods. Figure 8a displays the representative bulk XRD profiles from fine ash particles that distinguished two compositional groups. Group I (Units A-H) featured predominantly plagioclase (Pl) and augite (Aug) minerals. Group II (Units I-J) contains additional quartz and alunite phases among the plagioclase and augite minerals. The SEM-EDS analysis of a representative Unit I sample (Figure 8b) identified the secondary alteration minerals as alunite (Na-K-Al-S-O), quartz (Si-O), and aluminosilicate (Na-K-Si-O-Al) compositions. 4.7. Morphometric analysis of juvenile ash particles Particle shape analysis utilizing parameters of convexity, solidity, and form factor provided insights into fragmentation processes (e.g., Liu et al., 2015; Dürig et al., 2018; Nurfiani and Maisonneuve, 2018; Gurusinga et al., 2023). Convexity values less than one indicate increasing surface roughness and irregularity, while solidity measures closer to one represent denser ash particles (e.g., see Liu et al., 2015 and Nurfiani and Maisonneuve, 2018). The median values of morphometric parameters of YCT deposits exhibited two different groupings (Figure 9a). The stratigraphically lower Units A-F had median convexity, solidity, and form factor values below 0.9 versus higher values >0.9 in upper Units G- J. Bivariate plots of convexity versus form factor and solidity confirmed this classification (Figure 9b-c). Dense particles (BD) typically exhibited convexity ranging from 0.8-1, with vesicular particles (LV and BV) displaying a broader distribution from 0.5 to 1. 4.8. Textural variation of vesicular ash particle Based on the 2D vesicle size distribution analysis (Figure 10), vesicular ash (LV and BV) particles exhibited a bimodal distribution with diameters from 5 to 100 µm. The first mode (V1) predominantly featured spherical vesicles in the smaller size with a 5-20 µm range, whereas the second mode (V2) comprised larger vesicles (20-100 µm) exhibiting spherical, elongated, and coalesced shapes. Vesicles exceeding 100 µm diameter accounted for a low proportion due to limitations of analyzing small particle areas. Figure 11 plots bulk vesicularity, vesicle-free crystallinity, and vesicle number density (VND) by lithofacies. Most lithofacies exhibited an inverse correlation between higher bulk vesicularity and lower crystallinity, with the exception of Alt-aa lithofacies. The Pf lithofacies contained high bulk vesicularity and low VND, ranging from 0.2 to 0.64 in bulk vesicularity and 0.19 to 1.8x10 14 m -3 VND. The Sf and Ds-aa facies display identical bulk vesicularity (0.12-0.47) and VND (0.12 to 5.73x10 14 m -3 . Meanwhile, the Alt-aa lithofacies were characterized by low bulk vesicularity, VND, and crystallinity values relative to other lithofacies at 0.26, 0.23x10 14 m -3 , and 0.26, respectively (See Supplementary Materials 2 for detailed results). 5. Discussion 5.1. Types of fragmentation and their features The Young Ciremai eruption products exhibit magmatic and phreatomagmatic fragmentation characteristics. Magmatic fragmentation, typically associated with Vulcanian eruptions, occurs due to the sudden release of gas overpressure within the magma under the plug. This process leads to diverse grain size distributions and pyroclast types, including a variety of highly vesicular to dense, exhibiting irregular to blocky shapes (e.g., Wohletz, 1983; Pioli et al., 2008; D’Oriano et al., 2011; Miwa et al., 2013; White and Valentine, 2016; Gabellini et al., 2022). The fine ash (F1) proportions in the deposits show significant variability (Figure 13), ranging from 16% to 97% by weight, while coarser particles are represented by lower F2 values, which range from 1% to 43% by weight. This variability in grain size aligns with observations from other Vulcanian eruptions, such as the 2011 Shinmoedake eruption in Japan (e.g., Miyabuchi et al., 2013). In those cases, the distance from the vent and the fragmentation efficiency were significant factors influencing the distribution of grain sizes (e.g., Miyabuchi et al., 2013; Eychenne and Engwell, 2022). Phreatomagmatic fragmentation occurs from the interactions between magma and water, resulting in granulation due to thermal stress caused by rapid cooling and steam explosions (e.g., Wohletz, 1983; Liu et al., 2015; White and Valentine, 2016; Jones et al., 2022). This phenomenon produces relatively high fine ash proportions, characterized by F1 values ranging from 74 to 100 wt% and F2 values between 10 and 67 wt% (Figure 13). The substantial quantity of fine ash is comparable to phreatomagmatic deposits observed at Towada Volcano in Japan (e.g., Hiroi and Miyamoto, 2016). The presence of a significant amount of fine ash particles within a moist/wet eruption column facilitates the development of weakly- stratified aggregates (AP1) and coated particles (PC2) (Figure 7). This aggregation is attributed to electrostatic force and hydrostatic bonding during the eruption process (e.g., Brown et al., 2010; Brown et al., 2012; van Eaton et al., 2013; Hoult et al., 2022; Jones et al.,2022). Pyroclasts formed by phreatomagmatic eruptions are predominantly characterized by dense surfaces with blocky shapes, in contrast to the more diverse shapes found in magmatic pyroclasts (e.g., Delino and La Volpe, 1996; Liu et al., 2015; Dürig et al., 2018; Nurfiani & Maisonneuve, 2018; Dürig et al., 2021; Comida et al., 2022; Thivet et al., 2022; Gurusinga et al., 2023). Quantitative shape analysis and their distributions effectively distinguish between these two fragmentation mechanisms. The median convexity values for phreatomagmatic ash range from 0.88 to 0.93, which is slightly higher than the values of magmatic ash, which fall between 0.86 and 0.89. The distinct characteristics—such as grain size distributions, vesicularity, and morphological parameters—demonstrate that fragmentation style significantly impacts the deposits and eruption dynamics at Young Ciremai (e.g., Gurusinga et al., 2023). 5.2. Vesiculation processes in the volcanic conduit at Young Ciremai Vesiculation processes occur within the magma chamber, forming pheno-vesicles that exceed 100 μm in size, while in the conduit, matrix vesicles measuring less than 0.1 μm are formed. These processes are primarily driven by cooling-induced crystallization or by decompression (e.g., Toramaru, 2014; Suhendro et al., 2022; Suhendro et al., 2023). In ash-dominated tephra, vesicular ash particles from Young Ciremai typically preserve matrix vesicles, providing insights into the vesiculation processes influenced by a complex interplay of degassing, decompression, cooling, and fragmentation processes during magma ascent and eruption (e.g., Sparks 1978; Houghton and Wilson, 1989; Blower et al., 2002; Noguchi et al., 2006; Giachetti et al., 2010; Masotta et al., 2014; Toramaru, 2014; Fiege and Cichy, 2015; Le Gall and Pichavant, 2016; Colombier et al., 2022). Figure 11 illustrates that vesicular ash particles formed by Vulcanian and phreatomagmatic eruptions display a bimodal vesicle size distribution (VSD). This pattern suggests that the vesiculation processes were similar until magma fragmented at shallower depths. The larger vesicles (V2, >20 µm) are interpreted to have formed earlier in the deeper sections of the conduit (pre-fragmentation), growing as the result of gas expansion, coalescence, and Ostwald ripening (e.g., Sparks 1978; Blower et al., 2002; Noguchi et al., 2006; Giachetti et al., 2010; Masotta et al., 2014; Fiege and Cichy, 2015; Le Gall and Pichavant, 2016; Colombier et al., 2022). That process may occur during the magma ascent or stagnation in the shallower depth, leading to the formation of conduit plugs, gas accumulation, and subsequent rapid decompression (e.g., Melnik et al., 2005; Noguchi et al., 2006; Miwa and Toramaru, 2013; Miwa et al., 2013; Bain et al., 2019; Gabellini et al., 2022). The presence of multi-coalescent vesicles indicates magma with a relatively slow ascent and higher viscosity (e.g., Giachetti et al., 2010; Colombier et al., 2022). Conversely, the smaller vesicles (V1, <20 µm) are suggested to have formed near the surface during fragmentation. Although vesicular components exhibit a consistent vesicle size distribution (VSD), Figure 12 illustrates that phreatomagmatic fragmentation is characterized by a slightly lower vesicle number density (VND) and bulk vesicularity. This difference is likely due to rapid cooling when magma interacts with external water in shallow conduits (e.g., groundwater or crater lakes), inhibiting vesicle growth (e.g., Hiroi and Miyamoto, 2016). Assuming that VND may have a positive correlation with decompression rates (Toramaru, 2006; Shea, 2017), it can be inferred that magmatic fragmentation induced by sudden decompression (Pf and Sf lithofacies) results in higher decompression rates compared to phreatomagmatic fragmentation (Ds-aa and Alt-aa lithofacies). 5.3. Transitioning conduit structures: From magmatic to phreatomagmatic fragmentation Integrated analyses of lithofacies, grain size distribution (GSD), componentry, and the textures of juvenile ash particles indicate a prolonged evolution in the primary fragmentation mechanism at Young Ciremai. This evolution has shifted from magmatic to phreatomagmatic Vulcanian eruption styles, as illustrated in Figure 15. The evolution can be categorized into three distinct stages: Stage 1 is characterized by magmatic fragmentation, Stage 2 encompasses phreatomagmatic fragmentation associated with groundwater interactions, and Stage 3 is defined by phreatomagmatic fragmentation influenced by an underlying hydrothermal system. Stage 1 was characterized by magmatic Vulcanian activity, which resulted in the deposition of Pf and Sf lithofacies across Units A to E. Textural analysis of juvenile components—LV, BV, and BD—within these units indicates heterogeneous textures, showing trends of decreasing vesicle proportion and increasing crystal fraction from LV to BD components. This observation indicates a magma sequence during degassing, outgassing, and crystallization, which is associated with ascent and stalling within the volcanic edifice (Noguchi et al., 2006). The outgassing process promotes crystallization, as evidenced by the high crystallinity observed in BV particles and high crystal area fractions in BD particles. Additionally, the transition from rigid to viscoelastic fragmentation observed in these textures aligns with the process of magma stagnation/lava dome formation, which contributes to conduit plugging as suggested by various modeling studies (Alidibirov and Dingwell, 2000; Miwa and Toramaru, 2013; Miwa et al., 2013; Bain et al., 2019; Gabellini et al., 2022). The accumulation of exsolved gases within an impermeable plug leads to increased pressure, resulting in rapid decompression and a subsequent rise in vesicularity, marked by both bulk vesicularity and vesicle number density. During Stage 2, the development of phreatomagmatic eruptive activity was marked by the deposition of Unit F. Observations indicated a progressive increase in the proportion of ash aggregates through subsequent Units F to H, which infers progressive contribution of water. However, field observations in 2009 and 2022 indicate that Young Ciremai’s crater is predominantly dry, with the exception of temporary ponding during the rainy season in Crater-II (refer to Figure 3). Therefore, we interpret that the primary external water source driving the shift toward phreatomagmatic eruption styles is primarily linked to the shallow groundwater system located beneath the crater rather than the surface water source. Stage 3 marks by Unit I represent the current condition in the eruptive evolution. An upward trend in the proportions of oxidized (Ox) and hydrothermally altered (ALT) particles is observed within this unit, indicating the development of significant hydrothermal activity. The secondary mineral assemblages identified include quartz, alunite, and aluminosilicate, which suggest the presence of an acid hydrothermal alteration zone within the sub-volcanic hydrothermal system (e.g., Ohba and Kitade, 2005; Minami et al., 2016; Imura et al., 2021). A thorough textural identification of the ALT particles reveals various features such as replacement pseudomorph, infillings, and dissolution textures, all of which confirm the characteristics of acid alteration (e.g., Imura et al., 2021). It is posited that these acidic fluids arise from the interactions of magmatic gasses like CO 2 , SO 2 , and H 2 S with infiltrating waters (Giggenbach, 1997; Imura et al., 2021). Recent field observations have documented active solfatara activity between Crater-I and Crater-II, characterized by yellowish-white deposits, which align with the proposed conditions of Stage 3. Ongoing geophysical and geochemical monitoring of this active zone may provide insights into whether the current conditions align with the inferred hydrothermal states of Stage 2 or Stage 3. The shift from magmatic to phreatomagmatic fragmentation may be associated with developing groundwater systems at shallow depths beneath the crater, a process that occurs in response to the development of multiple craters, thereby expanding the crater’s area. At the same time, regional tectonic activity may enhance the fracture intensity, permeability, and water retention capacity within the crater region (e.g., Lamur et al., 2017). Such characteristics have been documented in other volcanoes exhibiting shallow hydrothermal systems and extensive multi-crater structures influenced by regional tectonics, including Mt. Tangkuban Perahu (e.g., Kartadinata et al., 2002; Angkasa et al., 2019), Mt. Ebeko (e.g., Kalacheva et al., 2016; Belousov et al., 2021; Kotenko et al., 2023), and Mt. Azuma-Jododaira (e.g., Yamamoto et al., 2005; Imura et al., 2021). 5.4. Future hazard potential The potential for future eruptive activity at Young Ciremai volcano presents a range of hazards that are contingent upon the eruption style. There is a possibility that magmatic eruptions may revert to the Vulcanian explosive behavior observed in Units C and E. Additionally, phreatomagmatic eruptions, which are associated with the interaction between magma and shallow groundwater systems, could also occur again, as evidenced in Units G and J. Given the current conditions, the presence of active sub-volcanic hydrothermal systems indicates the potential for hydrothermal or phreatic events, which can occur abruptly without precursory signals (Stix and Moor, 2018). Stratigraphic correlation indicates that Units C, E, G, and J feature deposits consistent with pyroclastic density currents (PDCs) generated by both Vulcanian and phreatomagmatic column collapses (Figure 2). Sustained eruptive column collapses could potentially generate PDCs that present significant risks due to their rapid mobility, high temperature, and potential for extensive runouts (Brown and Andrew, 2015). Specifically, Unit C exhibits substantial deposits, approximately 2 meters, located 5 km from the volcanic vent. In contrast, Units E, G, and J appear to be constrained to a runout distance of only a few kilometers, as indicated by observed thinning trends. However, it is important to note that future events could generate PDCs that threaten areas located further downstream from the vent if conditions allow. 6. Conclusion - The stratigraphic classification of the four lithofacies —Pf, Sf, Ds-aa, and Alt-aa—derived from ten tephra units (Units A-J) elucidates the evolution of explosive activity at Young Ciremai volcano. The Pf and Sf lithofacies are indicative of similar magmatic Vulcanian eruptions, whereas the Ds-aa and Alt-aa lithofacies signify phreatomagmatic eruptions. - Analysis of vesicular components resulting from phreatomagmatic fragmentation reveals a marginally lower vesicle number density (VND) and bulk vesicularity, with the vesicle size distribution (VSD) exhibiting bimodal characteristics. This distinction is likely attributable to the rapid cooling occurring when magma interacts with external water sources, such as groundwater or crater lakes, which inhibits vesicle growth. Conversely, during magmatic Vulcanian fragmentation, the absence of external water interaction might increase the conduit plug duration, accumulating the gas more and leading to rapid decompression. - The long-term transition from magmatic to increasingly phreatomagmatic fragmentation is correlated with the widening of the crater and regional tectonic activity, which enhances the fracture intensity, permeability, and water capacity. Furthermore, the acidic hydrothermal alteration observed is linked to the progressive development of subsurface hydrothermal conditions arising from the interaction between shallow groundwater and magmatic gasses, including CO 2 , SO 2 , and H 2 S. - The presence of a sub-volcanic hydrothermal system increases the potential of sudden phreatic or hydrothermal eruptions, alongside to the hazards caused by pyroclastic density currents from Vulcanian eruptions. These explosions might happen unpredictably, posing significant risks for those in proximity to the crater. Abbreviations CVC Ciremai Volcanic Complex GSD Grain Size Distribution Md Median diameter PDCs Pyroclastic density currents VEI Volcanic explosivity index YCT Young Ciremai Tephra Declarations Ethics approval and consent to participate “Not applicable” Consent for publication “Not applicable” Availability of data and materials All data analyzed and discussed in this study are available in supplementary data and from the corresponding author upon reasonable request. Competing Interests “The authors declare that they have no competing interests” Funding This research was supported by the Akita University Fellowship Program. Authors’ contributions WNH, TO, and MAG conducted geological investigations and rock sampling. WNH, TO, TH, MAG, MLAM, JNI, MA, and IAK developed the conceptual framework for the study and supervised the data collection and analysis. WNH and MLAM conducted the quantitative analysis of vesicularity and crystallinity. WNH and MAG digitized the boundary of ash particles and quantified the 2D shape parameter. WNH and F conducted the XRD analysis and interpretations of secondary mineral alterations. All authors reviewed and approved the final version of the manuscript. Acknowledgments We express our gratitude to A. A. Patria and R. M. Dwiantara, who imparted their knowledge on the utilization of R Studio software in our research. We also acknowledge I. Suhendro, G. N. R. B. Naen, and Zulfia for their insightful discussions and recommendations regarding our manuscript. “Kang” Slamet and “Bapa” Sanusi from Sadarehe, Majalengka, who provided invaluable support during the fieldwork. Furthermore, we express our thanks to Karoly Nemeth and Shimpei Uesawa for their role as reviewers, as well as to Takeshi Hasegawa as editor, for the constructive comments and reviews. 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J Volcanol Geotherm Res. 17: 31-63. https://doi.org/10.1016/0377-0273(83)90061-6 matic fragmentation: Yamamoto, T., Nakano, S., Ishizuka, and Y. (2021) Temporal variations of magma composition, eruption style and rate at Fuji Volcano, Japan. Earth Planets Space. 73:169. https://doi.org/10.1186/s40623-021-01505-1. Yamamoto, T. (2005) Eruptive history of Azuma volcano, NE Japan, during 7000 years: stratigraphy and magma plumbing system of the Azuma-Jododaira products. Jour.Geol Soc. Japan. 111 (2):94-110. https://doi.org/10.5575/geosoc.111.94 Badan Pusat Statistik Kabupaten Kuningan (2024) Jumlah penduduk menurut kecamatan dan agama yang dianut (people), 2021-2023. https://kuningankab.bps.go.id/indicator/12/104/1/jumlah-penduduk-menurut-kecamatan-dan-agama-yang-dianut.html. (access on 17/06/2024) Badan Pusat Satistik Kabupaten Majalengka (2024) Penduduk, Laju Pertumbuhan Penduduk, Distribusi Persentase Penduduk, Kepadatan Penduduk, Rasio Jenis Kelamin Penduduk Menurut Kecamatan di Kabupaten Majalengka, 2023. https://majalengkakab.bps.go.id/statictable/2024/03/08/1418/penduduk-laju-pertumbuhan-penduduk-distribusi-persentase-penduduk-kepadatan-penduduk-rasio-jenis-kelamin-penduduk-menurut-kecamatan-di-kabupaten-majalengka-2023-.html (access on 17/06/2024) Tables Table 1. Ash characteristics of the YCP component type. LV= light color vesicular, BV= black color vesicular, BD= black dense, GD= Grey dense, Ox= partially or fully oxidized, Alt= partially or fully altered, AA= Ash aggregate, FC= Free crystal. Microscope stereo observation SEM-BED observation Category Color Transparency Lustre Shape Surface texture Internal Texture (BSE image) LV Light brown, pale brown, yellow-brown, white Translucent-opaque Glossy Fluidal, irregular Rough A rich vesicle, less microlite, less groundmass area, spherical-coalescence vesicle, skeletal-swallowtail microlite BV Brown, black Opaque Glossy Fluidal, angular Rough Intermediate vesicle area, microlite rich, high groundmass area, coalescence vesicle, skeletal-swallowtail microlite BD Black Opaque Glossy Dense, angular, sharp edge Smooth Less vesicle area, high groundmass area, microlite rich, swallowtail microlite GD Grey, light grey Opaque Dull Dense, angular Smooth Free vesicle, High groundmass, rich microlite, euhedral microlite Ox Grey with spotted reddish, red brown, orange Opaque Dull Dense, angular Smooth Free vesicle, High groundmass, microlite rich, euhedral microlite, plagioclase partially altered Alt White, pinkies, pale yellow Opaque Dull Dense Smooth Dissolution texture. AA Grey, brown, pale yellow Opaque Dull Irregular, spherical-sub-spherical Rough Particle cluster (PC1) composed of FC and GD, coated particle (PC2) composed of GD coated by fine ash, poorly structured pellet (AP1) composed of fine ash of FC, AP2 is composed of massive to poorly sorted core rimmed by very fine ash of FC FC Colorless, white, dark greenish, olive green, brown, Translucent, transparent Glossy Cuspate, sharp edge, partly prismatic Smooth Clear boundary with Hackle marks fracture. Several FC contain remnant melt with vesicle and microlite Table 2. Characteristics of lithofacies from Young Ciremai tephra. Pf= pumiceous fall, Sf= scoriaceous fall, Ds-aa= Diffused stratification with ash aggregate, Alt-aa=Abundantly altered component with ash aggregate. ᵠ BV = bulk vesicularity, ᵠ Ph+Mph) = free-vesicle pheno+micropheno crystallinity. Stages 1 2 3 Lithofacies Pf Sf Ds-aa Alt-aa Unit Unit B Units A, C, D, and E Units F to G Units I and J Eruption Style Vulcanian to Sub-Plinian Vulcanian Phreatomagmatic Phreatomagmatic Distinct features Pumiceous Scoriaceous Ash aggregate Ash aggregate Abundant component LV, BV, BD LV, BV, BD BV,BD, AA BV, BD, AA, Alt Grain size parameter Ash (%) 26-96 55-100 88-100 93-100 F1 (%) 16-82 43-97 74-98 78-100 F2 (%) 1-12 6-43 10-53 67 Median shape parameter of ash particles Convexity 0.88 0.86-0.89 0.88-0.93 0.92-0.93 Solidity 0.91 0.86-0.92 0.91-0.93 0.91-0.93 Form factor 0.54 0.5-0.56 0.55-0.62 0.59-0.61 Internal texture parameter ᵠBv 0.18-0.65 0.13-0.47 0.10-0.44 0.08-0.26 ᵠPc+mpc 0.08-0.42 0.08-0.42 0.11-0.40 0.14-0.26 Nva (mm -2 ) 392-1714 267-4019 259-2647 260-468 VND (m -3 ) 0.19-1.8x10 14 0.12-5.73x10 14 0.11-3.5x10 14 0.12-0.23x10 14 Supplementary Files graphicalabstract.jpg supplementaryFigure1.pdf Supplementary1summaryofGSDparameter.xlsx Supplementary2vesicularityandcrystalinity.xlsx supplementary32Dshapeparameterofashparticle.xlsx Cite Share Download PDF Status: Published Journal Publication published 14 Feb, 2025 Read the published version in Earth, Planets and Space → Version 1 posted Reviewers agreed at journal 12 Dec, 2024 Reviewers invited by journal 12 Dec, 2024 Editor assigned by journal 11 Dec, 2024 First submitted to journal 11 Dec, 2024 Editorial decision: Minor Revision 17 Sep, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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09:34:52","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5017130/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5017130/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40623-025-02143-7","type":"published","date":"2025-02-14T15:57:58+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":71360652,"identity":"c4d09804-d8b8-4a11-8e6a-d63334f5e029","added_by":"auto","created_at":"2024-12-13 16:27:49","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":4387498,"visible":true,"origin":"","legend":"\u003cp\u003eGeological map of the Ciremai Volcanic Complex (CVC) and associated outcrop locations. \u003cstrong\u003ea.\u003c/strong\u003eSpatial distribution of active volcanoes in West Java, Indonesia, alongside the location of CVC. \u003cstrong\u003eb.\u003c/strong\u003e Delineation of the volcanic edifice on CVC into distinct phases of Gegerhalang, Ciremai-I, and Ciremai-II. \u003cstrong\u003ec.\u003c/strong\u003e Geological map representing the Young Ciremai edifice (modified from Situmorang et al., 1995).\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/5a3a3a644ca1d2d13ed8a671.png"},{"id":71362194,"identity":"9ddcc234-0b4c-4c55-8603-8aee4d5a1732","added_by":"auto","created_at":"2024-12-13 16:51:49","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":14082847,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of the outcrops and representative Units A-J within CVC. The\u003cstrong\u003e \u003c/strong\u003efigures illustrate that Units A-C are limited within a radius of 5 km from the crater (\u003cstrong\u003ea-d\u003c/strong\u003e), whereas Units D-E are well exposed across all sampling sites (\u003cstrong\u003ee-h\u003c/strong\u003e), and Units F-J are found in proximity to the crater (\u003cstrong\u003ei-o\u003c/strong\u003e) with \u003cstrong\u003em\u003c/strong\u003e is ash aggregate rich deposits from Unit G (see the Supplementary Figure 1 for the distribution location of each stratigraphic unit).\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/ec0b79df786e3a742ca6edae.png"},{"id":71361816,"identity":"b4cb4ac1-9e93-4562-a728-ce38abad3234","added_by":"auto","created_at":"2024-12-13 16:43:49","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":6427333,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphic correlation and outcrop characteristics at CVC. The stratigraphic correlation extends from the crater area to a distance of 5 km (Loc.1, Loc.2, Loc.3, loc.9\u003csub\u003eab\u003c/sub\u003e, Loc.16, Loc.17, Loc.18, and Loc.21). The soil boundary and tephra layer marker (e.g., the lower boundary for Unit D in Loc.17) represented by pale brown of fine ash layer identify the correlation between tephra units. The solid line (black) and the dashed line represent definitive and interpretative correlations, respectively.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/dd78d83ea2562726f9b042bf.png"},{"id":71360681,"identity":"fdf7142b-ade4-4782-94df-7de80fb3eaaa","added_by":"auto","created_at":"2024-12-13 16:27:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":8580122,"visible":true,"origin":"","legend":"\u003cp\u003eGeological features within the crater area of Young Ciremai volcano. \u003cstrong\u003ea.\u003c/strong\u003e A geological examination of the main vent area, which encompasses multiple layers of the lava flow (ML, IL-1, and IL-2) and tephra deposits (comprising Units C-J). \u003cstrong\u003eb.\u003c/strong\u003ePhotographic documentation (personal documentation in 2022) of active solfatara located between Crater-I and Crater-II, alongside secondary deposits (including various rockfalls and localized debris) situated at the crater base. \u003cstrong\u003ec.\u003c/strong\u003e Stratigraphic layers of YCT tephra derived from Units D-J. \u003cstrong\u003ed.\u003c/strong\u003e The documentation of crater condition in 2009 (personal documentation). \u003cstrong\u003ee.\u003c/strong\u003e Geological illustration depicting the current crater conditions. ML refers to massive lava, while IL refers to inter-layering lava.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/dfb1b46ccfed0717980a8aa2.png"},{"id":71360672,"identity":"ede71a5e-48d7-4630-8f57-266aaa158eed","added_by":"auto","created_at":"2024-12-13 16:27:50","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1464123,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphic variation of grain size parameters and grain size distribution (GSDs). \u003cstrong\u003ea.\u003c/strong\u003eStratigraphic features in proximity to the crater area. \u003cstrong\u003eb.\u003c/strong\u003e lithofacies and grain size parameter at 5 km from the vent. This section exhibits three distinct lithofacies, including scoriaceous fall (Sf), diffused stratification with ash aggregate (Ds-aa), and abundant altered components with ash aggregate (Alt-aa). The Sf lithofacies show a coarser particle size than Ds-aa and Alt-aa lithofacies, as evidenced by both median diameter (Md) and ash proportions. The pumiceous lithofacies (Pf) contain the coarsest particles than other lithofacies.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/d9df1d89d604634792a0eded.png"},{"id":71360949,"identity":"429949f7-f0ff-4624-8888-8ddba05840ee","added_by":"auto","created_at":"2024-12-13 16:35:49","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2762195,"visible":true,"origin":"","legend":"\u003cp\u003eMicrophotographs of representative ash components within Young Ciremai tephra. LV= light vesicular, BV= black vesicular, BD= black dense, GD= grey dense, Ox= partially-fully oxidized, Alt= partially-fully altered, AA= ash aggregate, FC= free crystal.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/81b4099e4c20c92e00a42079.png"},{"id":71361819,"identity":"ad79ff32-18e9-4984-885f-fe96636743cf","added_by":"auto","created_at":"2024-12-13 16:43:49","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":5405565,"visible":true,"origin":"","legend":"\u003cp\u003eMicrophotographs of representative ash aggregate observed Young Ciremai deposits. Representative samples from Unit J3 (\u003cstrong\u003ea-b\u003c/strong\u003e), Unit I1 (\u003cstrong\u003ec-f)\u003c/strong\u003e, Unit H2 (\u003cstrong\u003eg\u003c/strong\u003e), and Unit G1 (\u003cstrong\u003eh-i\u003c/strong\u003e). Pc1= ash cluster, Pc2= coated particles, Ap1= poorly-structured ash pellet, Ap2= ash pellet with concentric structure.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/fe583df05322e7d71a4f3417.png"},{"id":71360684,"identity":"891bb580-b6b9-4c28-90f7-613d1dfe3849","added_by":"auto","created_at":"2024-12-13 16:27:51","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1264547,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphic variations of ash component in Young Ciremai tephra. \u003cstrong\u003ea.\u003c/strong\u003e Variation of ash components in proximity to the crater region, \u003cstrong\u003eb.\u003c/strong\u003e at a distance of 5 km, and \u003cstrong\u003ec.\u003c/strong\u003e a composite distribution of the average component values within each stratigraphic unit. LV= light vesicular, BV= black vesicular, BD= black dense, GD= grey dense, Ox= partially-fully oxidized, Alt= altered, AA= ash aggregate, FC= free crystal.\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/1530579074fc51ad8aaf9992.png"},{"id":71360653,"identity":"c9ead0fe-0161-466f-853a-a6e9050ddc07","added_by":"auto","created_at":"2024-12-13 16:27:49","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":5109422,"visible":true,"origin":"","legend":"\u003cp\u003eThe occurrence of hydrothermal alteration minerals within tephra deposits from young Ciremai. \u003cstrong\u003ea.\u003c/strong\u003e X-ray diffraction (XRD) bulk analysis of fine ash particles indicates that secondary hydrothermal alteration minerals are frequent in Units I-J. This composition encompasses alunite (Alu), quartz (Qtz), and aluminosilicate minerals. The lines depicted in red, yellow, blue, and pink are Pf, Sf, Ds-aa, and Alt-aa lithofacies, respectively. \u003cstrong\u003eb. \u003c/strong\u003eRepresentative altered ash particles exhibiting dissolution features and the associated secondary minerals from EDS analysis.\u003c/p\u003e","description":"","filename":"Figure9.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/3fe35e935990530d762587ca.png"},{"id":71360679,"identity":"e5cb6ecb-818b-4257-8e8e-2643700d8b8c","added_by":"auto","created_at":"2024-12-13 16:27:51","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1341397,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea.\u003c/strong\u003eMedian values of Solidity, Convexity, and Form Factor of ash particles from Young Ciremai tephra. \u003cstrong\u003eb\u003c/strong\u003e-\u003cstrong\u003ec.\u003c/strong\u003e Convexity vs. Form Factor and Convexity vs. Solidity values of dense particles (BD) and vesicular particles (LV+BV). The plots show that BD particles have a relatively narrow convexity value ranging from 0.8 to 1, while the LV+BV exhibit a wider range between 0.5 to 1.\u003c/p\u003e","description":"","filename":"Figure10.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/0f6690af073c269a20c276f8.png"},{"id":71361820,"identity":"36a4c46e-454a-4c88-b233-9bd94132675f","added_by":"auto","created_at":"2024-12-13 16:43:49","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":874575,"visible":true,"origin":"","legend":"\u003cp\u003eVesicle size distribution from vesicular ash particles. The distribution exhibits bimodal characteristics with two modes, designated V1 and V2. The V1 mode corresponds to vesicles with a diameter ranging from 5 to 20µm, exhibiting a predominantly spherical shape. Conversely, the V2 mode comprises larger vesicles (exceeding 20 µm), which exhibit a range of morphological variations, including spherical, elongated, and coalesced forms.\u003c/p\u003e","description":"","filename":"Figure11.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/ee3fd04818e43252e83187c3.png"},{"id":71360665,"identity":"d8bca74a-b162-400b-8f91-ca6cf396913b","added_by":"auto","created_at":"2024-12-13 16:27:50","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":1801637,"visible":true,"origin":"","legend":"\u003cp\u003eTextural variation of vesicular-ash particles from YCT units. \u003cstrong\u003ea.\u003c/strong\u003e A graphical representation of bulk vesicularity in relation to free-vesicle crystallinity (comprising both phenocryst and microphenocryst). \u003cstrong\u003eb.\u003c/strong\u003e The correlation between bulk vesicularity and vesicle number density (VND) of vesicular particles. The Pf lithofacies of Unit B have a higher ᵠ\u003csub\u003eBV \u003c/sub\u003ewith lower VND. The Sf and Ds-aa lithofacies show a broad range of VND values. The alt-aa lithofacies are characterized by lower VND and ᵠopc+mpc. The larger vesicles predominantly display an irregular morphology, attributable to the coalescence of multiple vesicles, whereas the smaller vesicles are generally observed to be spherical in form.\u003c/p\u003e","description":"","filename":"Figure12.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/5bdcac5cc522fced9efb2fd7.png"},{"id":71360664,"identity":"b4abfa1d-b534-49d7-b84b-1ed3e8a944ab","added_by":"auto","created_at":"2024-12-13 16:27:49","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":427221,"visible":true,"origin":"","legend":"\u003cp\u003eThe F1-F2 plots illustrate the Young Ciremai tephra fall deposits compared to various studied eruption products from Vulcanian and sub-Plinian eruptions Shinmoedake tephra (Miyabuchi et al., 2013) and Plinian and phreatomagmatic tephra from Towada (Hiroi and Miyamoto, 2016). In YCT tephra deposits, the magmatic Vulcanian eruption type produces an extensive spectrum of F1 values (0-100%); in contrast, the phreatomagmatic eruption types exhibit a narrow F1 range (80-100%).\u003c/p\u003e","description":"","filename":"Figure13.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/2936995627c67831e2fb9bd9.png"},{"id":71360671,"identity":"79058c48-b14e-4578-a035-d10492c326d8","added_by":"auto","created_at":"2024-12-13 16:27:50","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":356593,"visible":true,"origin":"","legend":"\u003cp\u003eThe morphometric parameters of ash particles from Young Ciremai compared to other eruption styles. The plots confirm the two defining attributes of convexity values below 0.9 (including Units A-F) and contrasted with higher values of more than 0.9, which are associated with Units G-J. *Nurfiani and Maisonneuve (2018), ** Edwards et al. (2021).\u003c/p\u003e","description":"","filename":"Figure14.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/33a40c167d4be635fb356461.png"},{"id":71360670,"identity":"bc5e065b-3dd4-4382-a531-7d5face6c60b","added_by":"auto","created_at":"2024-12-13 16:27:50","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":4100443,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphical variation of tephra deposits and a schematic representation of the eruptive style evolution at Young Ciremai volcano. \u003cstrong\u003e1.\u003c/strong\u003e Stage-1, including Pf and Sf lithofacies, is characterized as a magmatic Vulcanian style. Ash aggregates are absent in this stage, with ash particles having lower convexity (median), higher bulk vesicularity, and crystallinity. \u003cstrong\u003e2. \u003c/strong\u003eStage-2 is represented by Ds-aa lithofacies, which correspond to the phreatomagmatic activity. Within this stage, the occurrence of ash aggregate is significantly more abundant, with ash particles demonstrating a slightly higher median convexity, lower bulk vesicularity, and crystallinity. \u003cstrong\u003e3.\u003c/strong\u003e Stage 3 is marked by increased altered particles from Unit I. This observation implies that the phreatomagmatic eruption shifted from Unit I to Unit J, which is associated with the subvolcanic hydrothermal system.\u003c/p\u003e","description":"","filename":"Figure15.png","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/6ced33920a4c443c8f80c946.png"},{"id":76487640,"identity":"7004595f-5ebc-48e1-bfb1-3e85a910df56","added_by":"auto","created_at":"2025-02-17 16:10:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":69486109,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/86a54da7-44ee-4059-b68b-1fecd86e84f1.pdf"},{"id":71360649,"identity":"b7a8087c-d8c5-40d1-b090-53522ef93601","added_by":"auto","created_at":"2024-12-13 16:27:49","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":109840,"visible":true,"origin":"","legend":"","description":"","filename":"graphicalabstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/dffb9e53fd137672c2c307fd.jpg"},{"id":71360666,"identity":"76729650-b98f-4da7-aa85-2c87a787a408","added_by":"auto","created_at":"2024-12-13 16:27:50","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":12786588,"visible":true,"origin":"","legend":"","description":"","filename":"supplementaryFigure1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/2e3a3d84faaab7d9badf7cdb.pdf"},{"id":71360657,"identity":"70a959d3-a9d2-4865-810f-343ae6e16283","added_by":"auto","created_at":"2024-12-13 16:27:49","extension":"xlsx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":16833,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementary1summaryofGSDparameter.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/37230836880ea440dccdf725.xlsx"},{"id":71360947,"identity":"7291c1b1-b55d-4f75-975c-d4b0b1d20288","added_by":"auto","created_at":"2024-12-13 16:35:49","extension":"xlsx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":21794,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementary2vesicularityandcrystalinity.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/ef0c15f86c525127a95329fd.xlsx"},{"id":71361817,"identity":"5c9c46e4-953f-45ea-8ac0-c33d41eb3bee","added_by":"auto","created_at":"2024-12-13 16:43:49","extension":"xlsx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":638641,"visible":true,"origin":"","legend":"","description":"","filename":"supplementary32Dshapeparameterofashparticle.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-5017130/v1/310eb014384ce90e72d07aa6.xlsx"}],"financialInterests":"","formattedTitle":"Transition from Magmatic to Phreatomagmatic Eruptions in Young Ciremai Volcano, Indonesia: Insights from Stratigraphy, Componentry, and Textural Analysis of Tephra Deposits","fulltext":[{"header":"1.\tIntroduction ","content":"\u003cp\u003eVulcanian eruptions are typically associated with magmas of intermediate compositions, such as basaltic andesite, andesite, and evolved dacitic magmas (e.g., Mercalli and Silvestri, 1891; Cas and Wright, 1987; Lockwood and Hazlett, 2010; Clarke et al., 2015; De Silva and Lindsay, 2015; Belousov et al., 2021). The eruptive style, first described by Mercalli and Silvestri (1891)\u0026nbsp;based on observations at Mt. Vulcano in the Aeolian Islands, is characterized by small to moderate, short-lived explosions spanning from seconds to minutes. These explosions generate dark-gray, ash-laden eruption clouds that rise several kilometers into the atmosphere (e.g., Cas and Wright, 1987; Lockwood and Hazlett, 2010; Clarke et al., 2015; Belousov et al., 2021). Ballistic fragments, such as dense volcanic bombs, often eject during these events, followed by intense shock waves due to the rapid decompression (e.g., Cas and Wright, 1987; Lockwood and Hazlett, 2010; Clarke et al., 2015; Belousov et al., 2021).\u003c/p\u003e\n\u003cp\u003eThe evolution of volcanic edifices and structures can promote the formation of groundwater or hydrothermal systems, which consequently influences eruption dynamics. The interaction between magma and external water contributes to the complexity and variability in fragmentation mechanisms, categorizing eruptions as magmatic, phreatomagmatic, phreatic, or hydrothermal (e.g., N\u0026eacute;meth and K\u0026oacute;sik, 2020; Montanaro et al., 2022). Young Ciremai in Indonesia has experienced phreatic-phreatomagmatic eruptions recently, notably in the years 1951, 1937-1938, 1775, 1772, and 1698 (Kusumadinata, 1979; Newhall and Dzurisin, 1988; Volcanological Survey of Indonesia, 2024; Global Volcanism Program, 2024). The eruption\u0026apos;s distribution was defined as phreatomagmatic deposits on the geological map from the volcanological survey of Indonesia (Situmorang et al. 1995). The geological maps indicate that the eruptive history deposits prior to 1698 might be related to both fragmentation mechanisms,\u0026nbsp;either magmatic or phreatomagmatic. Identification of these fragmentation mechanisms from the tephra deposits is essential for understanding the long-term evolution of conduit structure from magmatic to phreatomagmatic Vulcanian fragmentation in the Young Ciremai volcano.\u003c/p\u003e\n\u003cp\u003eThe objectives of this study are: 1) to elucidate the mechanisms of fragmentation and their key features through stratigraphy, grain size distribution, component analysis, bulk XRD analyses of fine ash particles, and petrographic and morphological study of ash particles; 2) to clarify the vesiculation processes of magma within the conduit during pre- and syn-fragmentation through quantitative petrographic analysis, including vesicle size distribution (VSD), vesicle number density (VND), bulk vesicularity, and bulk crystallinity; 3) to examine the evolution of conduit structure from magmatic to phreatomagmatic eruptions through temporal analysis of eruptive history as determined by stratigraphy; and 4) to determine the variability of potential hazards impacting approximately four million residents in nearby to CVC, estimated from Majalengka and Kuningan within a 4-8 km radius (BPS-Statistics Indonesia, 2024). \u0026nbsp;Also, the findings aim to improve long-term volcano monitoring and risk assessment, especially for low-frequency eruptive events with limited data, as exemplified by the Young Ciremai volcano.\u0026nbsp;\u003c/p\u003e"},{"header":"2.\tOverview of Ciremai Volcanic Complex ","content":"\u003cp\u003eThe Ciremai Volcanic Complex (CVC) is situated in the Java Trench (Figure 1a), a major tectonic feature formed by the convergence of the Indo-Australian and Eurasian plates in this region of Indonesia (e.g.,\u0026nbsp;Hamilton, 1979; Newhall and Dzurisin, 1988; Sendjadja et al., 2009; Setijadji, 2010; Bear-Crozier et al., 2016). Located on the border of Kuningan and Majalengka Regencies in West Java, Indonesia, the CVC comprises three main edifices: Putri, Gegerhalang, and Young Ciremai (Situmorang et al., 1995).\u0026nbsp;The geological map of CVC by Situmorang et al. (1995) in Figure 1c delineates four periods of volcanic activity. \u0026nbsp;The oldest Putri period is characterized by dissected morphology in the south flank and the porphyritic andesitic lava extrusion. \u0026nbsp;The subsequent Gegerhalang period (\u0026gt;40,800 years BP) constructed a horseshoe-shaped rim structure coincident with a northward migration of the eruptive vent, forming rough topography (Newhall and Dzurisin, 1988; Situmorang et al., 1995).\u003c/p\u003e\n\u003cp\u003eRenewed eruptive activity during the Ciremai-I (\u0026lt;13,350 years BP) and II (\u0026gt;13,350 years BP) period contributed to the growth of the Young Ciremai stratovolcano edifice (illustrated in Figure 1c). The Young Ciremai andesitic lava flow (Cl1 sample) contains plagioclase, pyroxenes, and opaque phenocrysts. \u0026nbsp;The explosive eruption deposits include one pyroclastic fallout deposit (Cpfa1) and two pyroclastic flow deposits (Cpfl1 and Cpfl2) (Situmorang et al., 1995). \u0026nbsp;Cpfa1 consists of a well-stratified tephra sequence consisting of pumice (1-5 cm), scoria, and lithic clasts, well exposed in the Argalingga area (Situmorang et al., 1995). Cpfl1 is a pyroclastic flow deposit with vertical facies change; the lower 30 m is unwelded, and the upper 6 m is welded volcanic breccia. \u0026nbsp;The deposit consists of pumice and lithic clasts in a grey-to-reddish ash matrix. On the other hand, Cpfl2 is a non-welded, 2- to 4-m-thick pyroclastic flow deposit. \u0026nbsp;Cpfl2 was radiocarbon dated from a charcoal sample to 13,350 years BP (Situmorang et al., 1995).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOngoing eruptive activity during the Ciremai-II period (\u0026lt; 13,350 years) has continued to the present day. Basaltic-andesitic lava flows erupted from central vents (Cl1, Cl3, Cl4, while flank eruptions produced basaltic lavas (Bl, Dl, Pl, and Sl) eruptions. Two pyroclastic fall deposits (Cpfa2 and Cpfa3) were also emplaced during this youngest period. Cpfa2 deposit is well-exposed in the Tegalijamuju area, comprising stratified lapilli and ash layers that contain pumice, scoria, and lithic. Cpfa3 deposits exposed near the summit area are phreatomagmatic eruption products, comprising ash aggregates along with lithic and pumice clasts (Situmorang et al., 1995).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMajor elements analysis of lava from CVC classified its composition as basaltic andesite and andesite, with SiO\u003csub\u003e2\u003c/sub\u003e ranging from 53-58% (Sendjaja et al., 2009). The CVC lavas are typically high-alumina basalts (HABs), With elevated Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (16.2 to 18.9 wt%), low MgO (3.2 to 6.7 wt%), and medium K\u003csub\u003e2\u003c/sub\u003eO (1.3 to 2.3 wt%). Modal mineralogy of the CVC lavas contains phenocrysts of plagioclase, pyroxene, olivine, and titanomagnetite (Hamzah et al., 2018; 2019).\u003c/p\u003e"},{"header":"3. Methods","content":"\u003cp\u003eWe identified 26 tephra outcrops from the Young Ciremai volcano along its western flank. Outcrops were distributed from the summit area to 5 km distance from the crater\u0026rsquo;s edge (Figure 1c). Individual tephra layers were carefully examined and correlated based on similarities in characteristics, including color, components, and soil boundaries (Lowe, 2011). Representative tephra samples were collected from three key localities \u0026ndash; the summit area (Loc. 21) and two locations approximately 5 km from the crater (Loc. 1 and Loc. 2). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe grain size distribution (GSD) of representative samples analysis was determined through dry sieving analysis of the 1ϕ intervals from -4 to 5ϕ. The key GSD parameters were calculated from the results: median grain size (Mdϕ), ash proportion (\u0026lt; -1ϕ), lapilli proportion, and cumulative weight percentages finer than 0ϕ (F1) and 4ϕ (F2) (See. Inman; 1952; Walker 1971; Miyabuchi et al., 2013). \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor component analysis, the 3-0ϕ size fractions (125\u0026micro;m - 1mm) were cleaned using an ultrasonic bath to remove any adhering material or coatings. Eight distinct component types (Table 1) were defined based on their color, shape, surface texture, luster, and transparency under a stereo microscope (Gaunt et al., 2016; Gomez-Arango et al., 2018; Thivet et al., 2022; Ohba et al., 2022; Benet et al., 2024). Component proportions were quantified by counting an average of 1000 grains within each of three sub-size fractions (3-2 ϕ, 2-1 ϕ, and 1-0ϕ).\u003c/p\u003e\n\u003cp\u003ePetrographic thin sections were made of coarse ash grains (1\u0026ndash;0 ϕ size fractions). This size range provides optimal visualization of the ash particle morphology and internal micro-textures (Comida et al., 2021). Thin sections were examined under a polarized light microscope and BSE microphotograph acquired by SEM JEOL JSM-IT300 LV at the Faculty of International Resource Sciences, Akita University. An accelerating voltage of 15 kV and a working distance of 15 mm were used for SEM-BSE observation. Vesicle and micro-phenocryst were observed at 100x magnification, while microlite textures were characterized at 1000x magnification. Vesicle shape was classified based on the visual assessment as, spherical, elongated, or coalesced, defined by Noguchi et al. (2006). Microlite morphologies were described using the terminology of Shea and Hammer (2013) for skeletal, swallowtail, and euhedral habits.\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eVesicles and crystal edges were manually digitized from the BSE micrograph using CorelDraw and were quantified using Image-J software. The bulk vesicularity (BV), vesicle-free crystallinity \u003cimg src=\"data:image/png;base64,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\" width=\"38\" height=\"18\"\u003e\u0026nbsp;and vesicle number density (VND) was calculated by following the equation from Suhendro (2024). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" style=\"width: 675px; height: 149.568px;\" width=\"675\" height=\"149.568\"\u003e\u003c/p\u003e\n\u003cp\u003eWhere N\u003csub\u003eAv\u003c/sub\u003e is the number density of vesicles in the unit area and D\u003csub\u003eV\u003c/sub\u003e is the average vesicle size.\u003c/p\u003e\n\u003cp\u003eImage analysis of ash particles was carried out to quantify 2D shape parameters related to fragmentation mechanism (Delino and La Volpe, 1996; Liu et al., 2015; D\u0026uuml;rig et al., 2018; Nurfiani \u0026amp; Maisonneuve, 2018; D\u0026uuml;rig et al., 2021; Comida et al., 2022; Thivet et al., 2022; Gurusinga et al., 2023). Ash particle images were imported into CorelDraw to outline particle perimeters manually. Traced boundaries were exported as black and white TIFF images. The PARTISAN script (Durig et al., 2018) in MATLAB was used to calculate the 2D shape parameters of convexity, solidity, and form factor (Delino and La Volpe, 1996; Liu et al., 2015).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe fine ash fractions (\u0026lt;4 ϕ) were analyzed to identify the secondary mineral alteration assemblages present within tephra units from YCT. X-ray diffractometer (XRD) analysis was conducted on a Rigaku MultiFlex using CuK\u0026alpha; radiation from 2 to 60\u003csup\u003eo\u003c/sup\u003e 2\u0026theta; at a scan rate of 0.25\u003csup\u003eo\u003c/sup\u003e/min from 2 to 60\u003csup\u003eo\u0026nbsp;\u003c/sup\u003e(Imura et al., 2021) at the Faculty of International Resource Sciences, Akita University. Operating conditions of 30 kV acceleration voltage and 16 mA filament current were used for the analysis. The qualitative mineral identification was carried out using the PDXL2 database. In addition, selected grains representing altered components were examined using an energy-dispersive spectrometer (EDS) to quantitatively assess the presence of secondary mineral alteration phases. \u0026nbsp;\u0026nbsp;\u003c/p\u003e"},{"header":"4.\tResults","content":"\u003cp\u003e\u003cstrong\u003e4.1.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eStratigraphy and lithofacies of Young Ciremai Tephra (YCT)\u0026nbsp;\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA total of 26 tephra outcrop localities were identified from the summit area to 5 km from the Young Ciremai volcano. Ten tephra deposits (Units A to J) were described below in stratigraphic order (Figure 2a). Units A, B, C, D, E, and G are widely distributed from the summit to a 5 km distance from the crater, while Units F, H, I, and J are concentrated near the crater.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit A\u003c/strong\u003e, as the oldest Unit, is exposedat locs 1 and 9 (Figure 2a), overlying a 30- cm thick pale-brown soil layer (Figure 2b). It consists of well-sorted, medium- to fine-grained ash with an average measured thickness of 10-12 cm, showing normal grading and subtle bioturbation. This Unit contains dark color particles, including scoria and dense rock fragments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit B\u003c/strong\u003e shows well-stratified tephra deposits and exhibits two different sequences in two localities. At Loc.1, Unit B consists of five sub-layers, of which the lower part comprises medium-fine ash overlain by stratified coarse-fine ash (Figure 2c). \u0026nbsp;The upper layers consist of pumiceous and scoriaceous coarse ash and lapilli. At Loc.9b, Unit B occurs as a single continuous gradational layer (Figure 2e). The lower part contains dark scoria and dense components, ranging from coarse ash to lapilli grain sizes. On the upper part, the facies transition to lighter pumiceous lapilli to medium-ash layer.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit C\u003c/strong\u003e is observed at Loc. 1 and 9, where it consists of four thin layers (C1–C4) separated by brown soil layers, with up to about 6 cm of the total thickness (Figure 2e). Each of the thin layers comprises a well-sorted, medium to fine ash, and subtle bioturbation features. Specifically, C1 and C2 layers are separated by a 2 cm soil layer, a 5 cm soil layer between C2 and C3, and a 5 cm soil layer between C3 and C4. This Unit is overlain by a prominent pale brown soil layer of 45-60 thickness. Dark scoria and dense fragments are present in Unit C. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit D\u003c/strong\u003e was identified at all outcrop localities, distributed within 5 km of the summit crater (Figure 2f-2i). \u0026nbsp;The total thickness ranges from 20-40 cm in the 5 km distance and increases to 86 cm in proximal exposures near the crater. This Unit contains a basal layer of light brown to pale gray fine-grained ash (Figure 2f-g). It is overlaid by scoria and dense rock fragments layers with multiple alternating medium and fine-grained ash layers.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit E\u003c/strong\u003e is well distributed within a 5-kilometer radius of the crater (Figure 2f-2i). In the 5 km radii, the total thickness is approximately 15-20 cm, consisting of alternating medium-fine ash facies. This unit, which reaches up to 62 cm thick in the proximal region, primarily consists of lapilli-fine ash, characterized by abundant scoria and dense block fragments. At Loc. 15, Loc. 16, and Loc. 17, we find a massive layer with abundant blocks to lapilli size, set in a fine ash matrix, overlying the tephra falls of Unit E. At Locs. 8 and 12, the top of the layer exhibits undulation and subtle bioturbation, overlaid by a 10-15 cm soil layer that develops between units D and E.\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit F\u003c/strong\u003e comprises 32 thin stratified layers with approximately 47 cm of total thickness, containing some layers with ash aggregates and diffused features (Figure 2j). The lowermost deposit is F1, a 3 cm massive coarse ash layer with a block sag structure. Overlying are alternating layers classified as F2 consisting of an alternation of thin medium-fine ash deposits. The uppermost is F3, which consists of a fine-grain layer. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit G\u003c/strong\u003e consists of three upward coarsening sub-units of approximately 40 cm total thickness (Figure 2k). Block sag structures were documented in fine ash layers throughout this Unit, which also contains ash aggregates and diffused layers (Figure 2m). The lower sub-unit (G1) comprises a set of medium-fine ash layers with 15 cm total thickness. The middle sub-unit (G2) is a coarse to fine ash layer set with 10 cm total thickness. The uppermost sub-unit (G3) consists of a set of lapilli-fine ash layers reaching 15 cm thickness. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit H\u003c/strong\u003e has an overall thickness of 60 cm divided into two defined sub-units containing abundant ash aggregates (Figure 2k-l). The lower sub-unit (H1) is a 25 cm thick medium-fine ash layer that exhibits a block sag structure. \u0026nbsp;The upper sub-unit (H2) consists of alternating medium-fine ash layers reaching 35 cm thickness and displaying diffuse stratification (Figure 2l). \u0026nbsp;This unit is overlain by a 3-5 cm dark brown soil layer, which separates between Units H and I.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit I\u003c/strong\u003e comprises a total thickness of approximately 23 cm consisting of two defined sub-units (Figure 2n-p). The lower sub-unit (I1) consists of a 9 cm thick fine ash layer with variations in colors: reddish, yellowish, and white-grey. The overlying upper sub-unit (I2) reaches 14 cm in thickness. It is characterized by a consolidated medium-fine ash layer that also contains ash aggregates. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUnit J\u003c/strong\u003e comprises the uppermost stratified sequence identified in YCT, reaching 30 cm in total thickness (Figure 2n-p). It consists of two sub-units. As the lower sub-unit (j1), has a thin fine ash layer pile. Overlying is a thicker sub-unit J2, characterized as a layer containing block and exhibiting block sag structures. Both sub-units range from yellowish to light color, which appear consolidated with dispersed ash aggregates.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe ten tephra units of YCT can be classified into four lithofacies based on their lithological features:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e1.\u0026nbsp;\u0026nbsp;Pumiceous fall\u003cstrong\u003e\u0026nbsp;(Pf lithofacies)\u0026nbsp;\u003c/strong\u003e– exemplified by pumice-rich clast Unit B.\u003c/p\u003e\n\u003cp\u003e2.\u0026nbsp;\u0026nbsp;Scoriaceous-blocky ash fall\u003cstrong\u003e\u0026nbsp;(Sf lithofacies)\u0026nbsp;\u003c/strong\u003e– occurred prominently in the lower-stratified Units A, C, D, and E.\u003c/p\u003e\n\u003cp\u003e3.\u0026nbsp;\u0026nbsp;Diffused stratification with ash aggregate\u003cstrong\u003e\u0026nbsp;(Ds-aa lithofacies)\u003c/strong\u003e – comprised of Units F, G, and H, featured variable ash aggregate abundances.\u003c/p\u003e\n\u003cp\u003e4.\u0026nbsp;\u0026nbsp;Abundantly altered components with ash aggregate \u003cstrong\u003e(Alt-aa lithofacies)\u003c/strong\u003e – stratified the uppermost Units I and J contained an abundant proportion of secondary alteration products.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.2.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eGeology of crater area\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe Young Ciremai volcanic edifice\u0026nbsp;shows an elongated crater rim that includes two major craters: Crater-I and Crater-II. The upper diameters of the craters estimate approximately 500 m and 850 m, whereas the lower diameters are approximately 150 m and 300 m, respectively. The crater morphology shows a typical funnel shape, characterized by inner walls with slopes between 30° and 90° and depths of 100 to 150 m. The crater surfaces consist of unconsolidated debris, comprising mud and rockfall fragments resulting from wall collapses (Figure 3B). The walls of the crater are composed of massive lava flows (ML), thick lava flows (IL-1), tephra from Unit C, thin lava flows (IL-2), and tephra from Units D to J (Figure 3A). The angular contacts that differentiate Unit G from Unit H are distinctly obvious (Figure 3C). Active solfataras and hydrothermal manifestations are situated along the border zone between Crater-I and Crater-II (Figure 3E).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.3.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eGrain size distributions (GSDs)\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eParticle size analysis of YCT deposits indicates that they are predominant in ash-size components (\u0026lt;1 mm), constituting over 50% of the samples from all stratigraphic units (Supplementary 1). Most GSD histograms exhibit unimodal distributions (Figure 4a). \u0026nbsp;In the crater area (Units D-J), two clusters of grain size were identified based on ash fraction and median particle size (Mdϕ) (Figure 4a). The first cluster (Units D-E) contained 50-60% of ash with Mdϕ ranges from 0 to 2ϕ. The second and larger cluster (Units F-J) is characterized by higher ash fractions (~80%) and finer Mdϕ ranges from 2 to 4ϕ. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAt 5 km from the crater (Units A-E), only Unit B comprises coarse ash and lapilli (maximum grain size -4ϕ). In contrast, the other Units, including Unit A, Unit C, Unit D, and Unit E, contained finer ash (maximum grain size -2ϕ; Figure 4b). \u0026nbsp;Unit B consisted of \u0026lt;90% ash with Mdϕ\u0026gt;2ϕ.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.4.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eVolcanic ash characteristics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAsh particles in YCT deposits were classified into eight categories based on the visual attributes (Figure 5): light-colored vesicular ash (LV), black vesicular ash (BV), black dense ash (BD), gray dense ash (GD), partially-completely oxidized ash (Ox), altered ash (Alt), free crystal (FC), and ash aggregate (AA). \u0026nbsp;These eight types were then grouped into two general categories: juvenile and non-juvenile components. The juvenile components included LV, BV, and BD clasts characterized by fresh surface textures, distinct mineral assemblages, and microlite textures. The non-juvenile components comprise GD, Ox, and Alt particles derived from external wall rock or older deposits reworked during eruptions. Table 1 summarizes the distinguishing characteristics of each ash category, with representative photomicrographs presented in Figure 4.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLV\u003c/strong\u003e ash particle exhibits fluidal to irregular shapes with a rough glossy surface. It has various colors from translucent to opaque in light-brown, pale-brown, and yellow-brown. Abundant vesicles are observed, varying from spherical to elongated shapes and coalesced forms. \u0026nbsp;It contains microlites with 10-30 µm size and skeletal to swallowtail morphology.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBV\u003c/strong\u003e ash particles appear as black, glossy fluidal ash with a rough surface. The vesicle proportion is less than in LV ash but the vesicle shape tends to be more coalesced. Microlite sizes range from 1-10 µm with swallowtail morphology.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBD\u003c/strong\u003e ash particles appear as black, glossy surfaces and blocky shapes with sharp edges. It has a higher microlite proportion compared to LV and BV ash types, ranging from 1-10 µm with swallowtail morphology and 10-30 µm with euhedral texture. \u0026nbsp;Fine nanolites (\u0026lt; 1 µm) of Fe-Ti oxides and mafic minerals also occur within interstices between microlites.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eGD\u003c/strong\u003e ash particles appear dull, light grey to grey, blocky ash shape with sharp edges. Euhedral microlites are commonly found in this ash type.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOX\u0026nbsp;\u003c/strong\u003eash particles appear dull, blocky shapes with sharp or rounded edges, exhibiting varied colors of grey, orange, and reddish colors. Microlite textures resemble those in GD particles with altered plagioclase.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eALT\u003c/strong\u003e ash particles, found exclusively in Units I and J, display discoloration ranging from white, grey, pink, and pale yellow. The BSE imaging of ALT particles depicts dissolution and hydrothermal infill textures, indicative of secondary alteration processes more intensive than the GD and OX components. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u0026nbsp;\u003cstrong\u003eAA\u003c/strong\u003e components comprise various types of ash aggregates. They were subdivided into four types (Figure 6) based on the morphological scheme of Brown et al. (2012): ash cluster (PC1), coated particles (PC2), poorly structured pellets (AP1), and pellets with concentric structure (AP2). PC1 and PC2 both exhibited irregular shapes, where PC1 comprised mixes of free crystal and lithic clast smaller than 100 µm (Figures 6g-i). PC2 featured lithic clast partly coated by fine ash less than \u0026lt;20 µm diameter (Figures 6a, b, d). \u0026nbsp;AP1 shows massive, spherical to subspherical forms constructed of loosely packed free crystals smaller than 50 µm (Figures 6c-f). AP2 has spherical to subspherical morphologies containing a core of massive or poorly structured ash 5-10 µm in diameter surrounded by an outer rim of finer ash less than 5 µm diameter (Figure 6c).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFC\u0026nbsp;\u003c/strong\u003eparticles represent a single crystal of mostly clinopyroxene and plagioclase. Some FC grains contain glass with vesicles along the rims, while others show an uncoated surface with hackle marks.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.5.\u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e \u003cstrong\u003eComponentry \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eComponentry analysis distinguished the YCT tephra deposits based on the occurrence and abundance of LV, AA, and ALT particles (Figure 7). The juvenile components of LV particles characterized the Pf and Sf lithofacies of Units A-E, while BV and BD particles occurred prominently across all lithofacies. AA particles dominated the Ds-aa and Alt-aa lithofacies, with only minor occurrences in Unit B5 of Pf lithofacies. Significant proportions of secondary ALT particles typified the Alt-aa lithofacies stratified as uppermost Units I-J.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.6.\u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp; Altered components compositions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMineral assemblages in fine ash particles and altered components were characterized using bulk XRD and SEM-EDS methods. Figure 8a displays the representative bulk XRD profiles from fine ash particles that distinguished two compositional groups. Group I (Units A-H) featured predominantly plagioclase (Pl) and augite (Aug) minerals. Group II (Units I-J) contains additional quartz and alunite phases among the plagioclase and augite minerals. The SEM-EDS analysis of a representative Unit I sample (Figure 8b) identified the secondary alteration minerals as alunite (Na-K-Al-S-O), quartz (Si-O), and aluminosilicate (Na-K-Si-O-Al) compositions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.7.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eMorphometric analysis of juvenile ash particles\u0026nbsp;\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eParticle shape analysis utilizing parameters of convexity, solidity, and form factor provided insights into fragmentation processes (e.g.,\u0026nbsp;Liu et al., 2015; Dürig et al., 2018; Nurfiani and Maisonneuve, 2018; Gurusinga et al., 2023). Convexity values less than one indicate increasing surface roughness and irregularity, while solidity measures closer to one represent denser ash particles (e.g., see Liu et al., 2015 and Nurfiani and Maisonneuve, 2018).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe median values of morphometric parameters of YCT deposits exhibited two different groupings (Figure 9a). The stratigraphically lower Units A-F had median convexity, solidity, and form factor values below 0.9 versus higher values \u0026gt;0.9 in upper Units G- J. Bivariate plots of convexity versus form factor and solidity confirmed this classification (Figure 9b-c). Dense particles (BD) typically exhibited convexity ranging from 0.8-1, with vesicular particles (LV and BV) displaying a broader distribution from 0.5 to 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.8.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eTextural variation of vesicular ash particle\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBased on the 2D vesicle size distribution analysis (Figure 10), vesicular ash (LV and BV) particles exhibited a bimodal distribution with diameters from 5 to 100 µm. The first mode (V1) predominantly featured spherical vesicles in the smaller size with a 5-20 µm range, whereas the second mode (V2) comprised larger vesicles (20-100 µm) exhibiting spherical, elongated, and coalesced shapes. Vesicles exceeding 100 µm diameter accounted for a low proportion due to limitations of analyzing small particle areas.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 11 plots bulk vesicularity, vesicle-free crystallinity, and vesicle number density (VND) by lithofacies. Most lithofacies exhibited an inverse correlation between higher bulk vesicularity and lower crystallinity, with the exception of Alt-aa lithofacies. The Pf lithofacies contained high bulk vesicularity and low VND, ranging from 0.2 to 0.64 in bulk vesicularity and 0.19 to 1.8x10\u003csup\u003e14\u0026nbsp;\u003c/sup\u003em\u003csup\u003e-3\u003c/sup\u003e VND. The Sf and Ds-aa facies display identical bulk vesicularity (0.12-0.47) and VND (0.12 to 5.73x10\u003csup\u003e14\u0026nbsp;\u003c/sup\u003em\u003csup\u003e-3\u003c/sup\u003e. Meanwhile, the Alt-aa lithofacies were characterized by low bulk vesicularity, VND, and crystallinity values relative to other lithofacies at 0.26, 0.23x10\u003csup\u003e14\u0026nbsp;\u003c/sup\u003em\u003csup\u003e-3\u003c/sup\u003e, and 0.26, respectively (See Supplementary Materials 2 for detailed results). \u0026nbsp;\u003c/p\u003e"},{"header":"5.\tDiscussion","content":"\u003cp\u003e\u003cstrong\u003e5.1.\u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eTypes of fragmentation and their features\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Young Ciremai eruption products exhibit magmatic and phreatomagmatic fragmentation characteristics. Magmatic fragmentation, typically associated with Vulcanian eruptions, occurs due to the sudden release of gas overpressure within the magma under the plug. This process leads to diverse grain size distributions and pyroclast types, including a variety of highly vesicular to dense, exhibiting irregular to blocky shapes (e.g., Wohletz, 1983; Pioli et al., 2008; D’Oriano et al., 2011; Miwa et al., 2013; White and Valentine, 2016; Gabellini et al., 2022). The fine ash (F1) proportions in the deposits show significant variability (Figure 13), ranging from 16% to 97% by weight, while coarser particles are represented by lower F2 values, which range from 1% to 43% by weight. This variability in grain size aligns with observations from other Vulcanian eruptions, such as the 2011 Shinmoedake eruption in Japan (e.g., Miyabuchi et al., 2013). In those cases, the distance from the vent and the fragmentation efficiency were significant factors influencing the distribution of grain sizes (e.g., Miyabuchi et al., 2013; Eychenne and Engwell, 2022).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePhreatomagmatic fragmentation occurs from the interactions between magma and water, resulting in granulation due to thermal stress caused by rapid cooling and steam explosions (e.g., Wohletz, 1983; Liu et al., 2015; White and Valentine, 2016; Jones et al., 2022). This phenomenon produces relatively high fine ash proportions, characterized by F1 values ranging from 74 to 100 wt% and F2 values between 10 and 67 wt% (Figure 13). The substantial quantity of fine ash is comparable to phreatomagmatic deposits observed at Towada Volcano in Japan (e.g., Hiroi and Miyamoto, 2016). The presence of a significant amount of fine ash particles within a moist/wet eruption column facilitates the development of weakly- stratified aggregates (AP1) and coated particles (PC2) (Figure 7). This aggregation is attributed to electrostatic force and hydrostatic bonding during the eruption process (e.g., Brown et al., 2010; Brown et al., 2012; van Eaton et al., 2013; Hoult et al., 2022; Jones et al.,2022).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePyroclasts formed by phreatomagmatic eruptions are predominantly characterized by dense surfaces with blocky shapes, in contrast to the more diverse shapes found in magmatic pyroclasts (e.g., Delino and La Volpe, 1996; Liu et al., 2015; Dürig et al., 2018; Nurfiani \u0026amp; Maisonneuve, 2018; Dürig et al., 2021; Comida et al., 2022; Thivet et al., 2022; Gurusinga et al., 2023). Quantitative shape analysis and their distributions effectively distinguish between these two fragmentation mechanisms. The median convexity values for phreatomagmatic ash range from 0.88 to 0.93, which is slightly higher than the values of magmatic ash, which fall between 0.86 and 0.89. The distinct characteristics—such as grain size distributions, vesicularity, and morphological parameters—demonstrate that fragmentation style significantly impacts the deposits and eruption dynamics at Young Ciremai (e.g., Gurusinga et al., 2023).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e5.2.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eVesiculation processes in the volcanic conduit at Young Ciremai\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eVesiculation processes occur within the magma chamber, forming pheno-vesicles that exceed 100 μm in size, while in the conduit, matrix vesicles measuring less than 0.1 μm are formed. These processes are primarily driven by cooling-induced crystallization or by decompression (e.g., Toramaru, 2014; Suhendro et al., 2022; Suhendro et al., 2023). In ash-dominated tephra, vesicular ash particles from Young Ciremai typically preserve matrix vesicles, providing insights into the vesiculation processes influenced by a complex interplay of degassing, decompression, cooling, and fragmentation processes during magma ascent and eruption (e.g., Sparks 1978; Houghton and Wilson, 1989; Blower et al., 2002; Noguchi et al., 2006; Giachetti et al., 2010; Masotta et al., 2014; Toramaru, 2014; Fiege and Cichy, 2015; Le Gall and Pichavant, 2016; Colombier et al., 2022).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 11 illustrates that vesicular ash particles formed by Vulcanian and phreatomagmatic eruptions display a bimodal vesicle size distribution (VSD). This pattern suggests that the vesiculation processes were similar until magma fragmented at shallower depths. The larger vesicles (V2, \u0026gt;20 µm) are interpreted to have formed earlier in the deeper sections of the conduit (pre-fragmentation), growing as the result of gas expansion, coalescence, and Ostwald ripening (e.g., Sparks 1978; Blower et al., 2002; Noguchi et al., 2006; Giachetti et al., 2010; Masotta et al., 2014; Fiege and Cichy, 2015; Le Gall and Pichavant, 2016; Colombier et al., 2022). That process may occur during the magma ascent or stagnation in the shallower depth, leading to the formation of conduit plugs, gas accumulation, and subsequent rapid decompression (e.g., Melnik et al., 2005; Noguchi et al., 2006; Miwa and Toramaru, 2013; Miwa et al., 2013; Bain et al., 2019; Gabellini et al., 2022). The presence of multi-coalescent vesicles indicates magma with a relatively slow ascent and higher viscosity (e.g., Giachetti et al., 2010; Colombier et al., 2022). \u0026nbsp; Conversely, the smaller vesicles (V1, \u0026lt;20 µm) are suggested to have formed near the surface during fragmentation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAlthough vesicular components exhibit a consistent vesicle size distribution (VSD), Figure 12 illustrates that phreatomagmatic fragmentation is characterized by a slightly lower vesicle number density (VND) and bulk vesicularity. This difference is likely due to rapid cooling when magma interacts with external water in shallow conduits (e.g., groundwater or crater lakes), inhibiting vesicle growth (e.g., Hiroi and Miyamoto, 2016). Assuming that VND may have a positive correlation with decompression rates (Toramaru, 2006; Shea, 2017), it can be inferred that magmatic fragmentation induced by sudden decompression (Pf and Sf lithofacies) results in higher decompression rates compared to phreatomagmatic fragmentation (Ds-aa and Alt-aa lithofacies).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e5.3.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eTransitioning conduit structures: From magmatic to phreatomagmatic fragmentation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIntegrated analyses of lithofacies, grain size distribution (GSD), componentry, and the textures of juvenile ash particles indicate a prolonged evolution in the primary fragmentation mechanism at Young Ciremai. This evolution has shifted from magmatic to phreatomagmatic Vulcanian eruption styles, as illustrated in Figure 15. The evolution can be categorized into three distinct stages: Stage 1 is characterized by magmatic fragmentation, Stage 2 encompasses phreatomagmatic fragmentation associated with groundwater interactions, and Stage 3 is defined by phreatomagmatic fragmentation influenced by an underlying hydrothermal system.\u003c/p\u003e\n\u003cp\u003eStage 1 was characterized by magmatic Vulcanian activity, which resulted in the deposition of Pf and Sf lithofacies across Units A to E. Textural analysis of juvenile components—LV, BV, and BD—within these units indicates heterogeneous textures, showing trends of decreasing vesicle proportion and increasing crystal fraction from LV to BD components. This observation indicates a magma sequence during degassing, outgassing, and crystallization, which is associated with ascent and stalling within the volcanic edifice (Noguchi et al., 2006). The outgassing process promotes crystallization, as evidenced by the high crystallinity observed in BV particles and high crystal area fractions in BD particles. Additionally, the transition from rigid to viscoelastic fragmentation observed in these textures aligns with the process of magma stagnation/lava dome formation, which contributes to conduit plugging as suggested by various modeling studies (Alidibirov and Dingwell, 2000; Miwa and Toramaru, 2013; Miwa et al., 2013; Bain et al., 2019; Gabellini et al., 2022).\u0026nbsp;The accumulation of exsolved gases within an impermeable plug leads to increased pressure, resulting in rapid decompression and a subsequent rise in vesicularity, marked by both bulk vesicularity and vesicle number density.\u003c/p\u003e\n\u003cp\u003eDuring Stage 2, the development of phreatomagmatic eruptive activity was marked by the deposition of Unit F. Observations indicated a progressive increase in the proportion of ash aggregates through subsequent Units F to H, which infers progressive contribution of water. However, field observations in 2009 and 2022 indicate that Young Ciremai’s crater is predominantly dry, with the exception of temporary ponding during the rainy season in Crater-II (refer to Figure 3). Therefore, we interpret that the primary external water source driving the shift toward phreatomagmatic eruption styles is primarily linked to the shallow groundwater system located beneath the crater rather than the surface water source.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eStage 3 marks by Unit I represent the current condition in the eruptive evolution. An upward trend in the proportions of oxidized (Ox) and hydrothermally altered (ALT) particles is observed within this unit, indicating the development of significant hydrothermal activity. The secondary mineral assemblages identified include quartz, alunite, and aluminosilicate, which suggest the presence of an acid hydrothermal alteration zone within the sub-volcanic hydrothermal system (e.g., Ohba and Kitade, 2005; Minami et al., 2016; Imura et al., 2021). A thorough textural identification of the ALT particles reveals various features such as replacement pseudomorph, infillings, and dissolution textures, all of which confirm the characteristics of acid alteration (e.g., Imura et al., 2021). It is posited that these acidic fluids arise from the interactions of magmatic gasses like CO\u003csub\u003e2\u003c/sub\u003e, SO\u003csub\u003e2\u003c/sub\u003e, and H\u003csub\u003e2\u003c/sub\u003eS with infiltrating waters (Giggenbach, 1997; Imura et al., 2021). Recent field observations have documented active solfatara activity between Crater-I and Crater-II, characterized by yellowish-white deposits, which align with the proposed conditions of Stage 3. Ongoing geophysical and geochemical monitoring of this active zone may provide insights into whether the current conditions align with the inferred hydrothermal states of Stage 2 or Stage 3.\u003c/p\u003e\n\u003cp\u003eThe shift from magmatic to phreatomagmatic fragmentation may be associated with developing groundwater systems at shallow depths beneath the crater, a process that occurs in response to the development of multiple craters, thereby expanding the crater’s area. At the same time, regional tectonic activity may enhance the fracture intensity, permeability, and water retention capacity within the crater region (e.g., Lamur et al., 2017). Such characteristics have been documented in other volcanoes exhibiting shallow hydrothermal systems and extensive multi-crater structures influenced by regional tectonics, including Mt. Tangkuban Perahu (e.g., Kartadinata et al., 2002; Angkasa et al., 2019), Mt. Ebeko (e.g., Kalacheva et al., 2016; Belousov et al., 2021; Kotenko et al., 2023), and Mt. Azuma-Jododaira (e.g., Yamamoto et al., 2005; Imura et al., 2021).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e5.4.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eFuture hazard potential\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe potential for future eruptive activity at Young Ciremai volcano presents a range of hazards that are contingent upon the eruption style. There is a possibility that magmatic eruptions may revert to the Vulcanian explosive behavior observed in Units C and E. Additionally, phreatomagmatic eruptions, which are associated with the interaction between magma and shallow groundwater systems, could also occur again, as evidenced in Units G and J. Given the current conditions, the presence of active sub-volcanic hydrothermal systems indicates the potential for hydrothermal or phreatic events, which can occur abruptly without precursory signals (Stix and Moor, 2018).\u003c/p\u003e\n\u003cp\u003eStratigraphic correlation indicates that Units C, E, G, and J feature deposits consistent with pyroclastic density currents (PDCs) generated by both Vulcanian and phreatomagmatic column collapses (Figure 2). Sustained eruptive column collapses could potentially generate PDCs that present significant risks due to their rapid mobility, high temperature, and potential for extensive runouts (Brown and Andrew, 2015). Specifically, Unit C exhibits substantial deposits, approximately 2 meters, located 5 km from the volcanic vent. In contrast, Units E, G, and J appear to be constrained to a runout distance of only a few kilometers, as indicated by observed thinning trends. However, it is important to note that future events could generate PDCs that threaten areas located further downstream from the vent if conditions allow.\u003c/p\u003e\n\n\n\n\n"},{"header":"6. Conclusion ","content":"\u003cp\u003e- The stratigraphic classification of the four lithofacies —Pf, Sf, Ds-aa, and Alt-aa—derived from ten tephra units (Units A-J) elucidates the evolution of explosive activity at Young Ciremai volcano. The Pf and Sf lithofacies are indicative of similar magmatic Vulcanian eruptions, whereas the Ds-aa and Alt-aa lithofacies signify phreatomagmatic eruptions.\u0026nbsp;\u003c/p\u003e\u003cp\u003e- Analysis of vesicular components resulting from phreatomagmatic fragmentation reveals a marginally lower vesicle number density (VND) and bulk vesicularity, with the vesicle size distribution (VSD) exhibiting bimodal characteristics. This distinction is likely attributable to the rapid cooling occurring when magma interacts with external water sources, such as groundwater or crater lakes, which inhibits vesicle growth. Conversely, during magmatic Vulcanian fragmentation, the absence of external water interaction might increase the conduit plug duration, accumulating the gas more and leading to rapid decompression.\u003c/p\u003e\u003cp\u003e- The long-term transition from magmatic to increasingly phreatomagmatic fragmentation is correlated with the widening of the crater and regional tectonic activity, which enhances the fracture intensity, permeability, and water capacity. Furthermore, the acidic hydrothermal alteration observed is linked to the progressive development of subsurface hydrothermal conditions arising from the interaction between shallow groundwater and magmatic gasses, including CO\u003csub\u003e2\u003c/sub\u003e, SO\u003csub\u003e2\u003c/sub\u003e, and H\u003csub\u003e2\u003c/sub\u003eS.\u0026nbsp;\u0026nbsp;\u003c/p\u003e\u003cp\u003e- The presence of a sub-volcanic hydrothermal system increases the potential of sudden phreatic or hydrothermal eruptions, alongside to the hazards caused by pyroclastic density currents from Vulcanian eruptions. These explosions might happen unpredictably, posing significant risks for those in proximity to the crater.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCVC\u0026nbsp; \u0026nbsp;\u0026nbsp;Ciremai Volcanic Complex\u003c/p\u003e\n\u003cp\u003eGSD\u0026nbsp; \u0026nbsp;\u0026nbsp;Grain Size Distribution\u003c/p\u003e\n\u003cp\u003eMd\u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Median diameter\u003c/p\u003e\n\u003cp\u003ePDCs\u0026nbsp; \u0026nbsp;Pyroclastic density currents\u003c/p\u003e\n\u003cp\u003eVEI\u0026nbsp; \u0026nbsp; \u0026nbsp;Volcanic explosivity index\u003c/p\u003e\n\u003cp\u003eYCT \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Young Ciremai Tephra\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e“Not applicable”\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e“Not applicable”\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data analyzed and discussed in this study are available in supplementary data and from the corresponding author upon reasonable request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e“The authors declare that they have no competing interests”\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Akita University Fellowship Program.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors’ contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWNH, TO, and MAG conducted geological investigations and rock sampling. WNH, TO, TH, MAG, MLAM, JNI, MA, and IAK developed the conceptual framework for the study and supervised the data collection and analysis. WNH and MLAM conducted the quantitative analysis of vesicularity and crystallinity. WNH and MAG digitized the boundary of ash particles and quantified the 2D shape parameter. WNH and F conducted the XRD analysis and interpretations of secondary mineral alterations. All authors reviewed and approved the final version of the manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe express our gratitude to A. A. Patria and R. M. Dwiantara, who imparted their knowledge on the utilization of R Studio software in our research.\u0026nbsp;We also acknowledge I. Suhendro, G. N. R. B. Naen, and Zulfia for their insightful discussions and recommendations regarding our manuscript.\u0026nbsp;“Kang” Slamet and “Bapa” Sanusi from Sadarehe, Majalengka, who provided invaluable support during the fieldwork. Furthermore, we express our thanks to Karoly Nemeth and Shimpei Uesawa for their role as reviewers, as well as to Takeshi Hasegawa as editor, for the constructive comments and reviews.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors’ information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eDepartment of Earth Resource Sciences, Faculty of International Resource Sciences, Akita University, 1-1 Tegata Gakuenmachi, Akita 010-8502, Japan.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e2\u003c/sup\u003eDepartment of Geological Engineering, Faculty of Earth Sciences and Technology, Institut Teknologi Bandung, Jl. Ganesha No. 10, Bandung 40132, Indonesia.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e3\u003c/sup\u003eDepartment of Geology Engineering, Universitas Jenderal Soedirman, Jl. Mayjend Soengkono, Purbalingga 533371, Indonesia.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e4\u003c/sup\u003eCenter for Regional Revitalization in Research and Education, Akita University, 1-1, Tegata Gakuenmachi, Akita 010-8502, Japan.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAlidibirov, M., Dingwell D. B. (2000). Three fragmentation mechanisms for highly viscous magma under rapid decompression. J Volcanol Geotherm Res. 100: issues 1-4: 413-421. https://doi.org/10.1016/S0377-0273(00)00149-9\u003c/li\u003e\n\u003cli\u003eAngkasa, S. S., Ohba, T., Imura, T., Setiawan, I., Roasana, M. F. (2019) Tephra-stratigraphy and ash componentry studies of proximal volcanic product at Mount Tangkuban Parahu Indonesia: an insight to Holocene volcanic activity. 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(access on 17/06/2024)\u003c/li\u003e\n\u003cli\u003eBadan Pusat Satistik Kabupaten Majalengka (2024) Penduduk, Laju Pertumbuhan Penduduk, Distribusi Persentase Penduduk, Kepadatan Penduduk, Rasio Jenis Kelamin Penduduk Menurut Kecamatan di Kabupaten Majalengka, 2023. https://majalengkakab.bps.go.id/statictable/2024/03/08/1418/penduduk-laju-pertumbuhan-penduduk-distribusi-persentase-penduduk-kepadatan-penduduk-rasio-jenis-kelamin-penduduk-menurut-kecamatan-di-kabupaten-majalengka-2023-.html (access on 17/06/2024)\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Ash characteristics of the YCP component type. LV= light color vesicular, BV= black color vesicular, BD= black dense, GD= Grey dense, Ox= partially or fully oxidized, Alt= partially or fully altered, AA= Ash aggregate, FC= Free crystal.\u003c/p\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"878\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 74px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"5\" valign=\"bottom\" style=\"width: 553px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMicroscope stereo observation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 251px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSEM-BED observation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 74px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCategory\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 116px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eColor\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 116px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTransparency\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 71px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLustre\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 126px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eShape\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSurface texture\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 251px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInternal Texture (BSE image)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 74px;\"\u003e\n \u003cp\u003eLV\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eLight brown, pale brown, yellow-brown, white\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eTranslucent-opaque\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\n \u003cp\u003eGlossy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003eFluidal, irregular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eRough\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 251px;\"\u003e\n \u003cp\u003eA rich vesicle, less microlite, less groundmass area, spherical-coalescence vesicle, skeletal-swallowtail microlite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 74px;\"\u003e\n \u003cp\u003eBV\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eBrown, black\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eOpaque\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\n \u003cp\u003eGlossy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003eFluidal, angular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eRough\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 251px;\"\u003e\n \u003cp\u003eIntermediate vesicle area, microlite rich, high groundmass area, coalescence vesicle, skeletal-swallowtail microlite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 74px;\"\u003e\n \u003cp\u003eBD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eBlack\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eOpaque\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\n \u003cp\u003eGlossy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003eDense, angular, sharp edge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eSmooth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 251px;\"\u003e\n \u003cp\u003eLess vesicle area, high groundmass area, microlite rich, swallowtail microlite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 74px;\"\u003e\n \u003cp\u003eGD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eGrey, light grey\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eOpaque\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\n \u003cp\u003eDull\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003eDense, angular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eSmooth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 251px;\"\u003e\n \u003cp\u003eFree vesicle, High groundmass, rich microlite, euhedral microlite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 74px;\"\u003e\n \u003cp\u003eOx\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eGrey with spotted reddish, red brown, orange\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eOpaque\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\n \u003cp\u003eDull\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003eDense, angular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eSmooth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 251px;\"\u003e\n \u003cp\u003eFree vesicle, High groundmass, microlite rich, euhedral microlite, plagioclase partially altered\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 74px;\"\u003e\n \u003cp\u003eAlt\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eWhite, pinkies, pale yellow\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eOpaque\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\n \u003cp\u003eDull\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003eDense\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eSmooth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 251px;\"\u003e\n \u003cp\u003eDissolution texture.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 74px;\"\u003e\n \u003cp\u003eAA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eGrey, brown, pale yellow\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eOpaque\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\n \u003cp\u003eDull\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003eIrregular, spherical-sub-spherical\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eRough\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 251px;\"\u003e\n \u003cp\u003eParticle cluster (PC1) composed of FC and GD, coated particle (PC2) composed of GD coated by fine ash, poorly structured pellet (AP1) composed of fine ash of FC, AP2 is composed of massive to poorly sorted core rimmed by very fine ash of FC\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 74px;\"\u003e\n \u003cp\u003eFC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eColorless, white, dark greenish, olive green, \u0026nbsp;brown,\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 116px;\"\u003e\n \u003cp\u003eTranslucent, transparent\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 71px;\"\u003e\n \u003cp\u003eGlossy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003eCuspate, sharp edge, partly prismatic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eSmooth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 251px;\"\u003e\n \u003cp\u003eClear boundary with Hackle marks fracture. Several FC contain remnant melt with vesicle and microlite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u003c/strong\u003e Characteristics of lithofacies from Young Ciremai tephra. Pf= pumiceous fall, Sf= scoriaceous fall, Ds-aa= Diffused stratification with ash aggregate, Alt-aa=Abundantly altered component with ash aggregate. ᵠ\u003csub\u003eBV\u003c/sub\u003e= bulk vesicularity, ᵠ\u003csub\u003ePh+Mph)\u0026nbsp;\u003c/sub\u003e= free-vesicle pheno+micropheno crystallinity.\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"101%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 14px;\"\u003e\n \u003cp\u003eStages\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 32px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003eLithofacies\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePf\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSf\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDs-aa\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAlt-aa\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003eUnit\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eUnit B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eUnits A, C, D, and E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003eUnits F to G\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003eUnits I and J\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003eEruption Style\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eVulcanian to Sub-Plinian\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eVulcanian\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003ePhreatomagmatic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003ePhreatomagmatic\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003eDistinct features\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003ePumiceous\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eScoriaceous\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003eAsh aggregate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003eAsh aggregate\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003eAbundant component\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eLV, BV, BD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eLV, BV, BD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003eBV,BD, AA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003eBV, BD, AA, Alt\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 14px;\"\u003e\n \u003cp\u003eGrain size parameter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eAsh (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e26-96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e55-100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e88-100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e93-100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eF1 (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e16-82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e43-97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e74-98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e78-100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eF2 (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e1-12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e6-43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e10-53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 14px;\"\u003e\n \u003cp\u003eMedian shape parameter of ash particles\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eConvexity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.86-0.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.88-0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.92-0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eSolidity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.86-0.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.91-0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.91-0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eForm factor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.5-0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.55-0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.59-0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 14px;\"\u003e\n \u003cp\u003eInternal texture parameter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eᵠBv\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.18-0.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.13-0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.10-0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.08-0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eᵠPc+mpc\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.08-0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.08-0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.11-0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.14-0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eNva (mm\u003csup\u003e-2\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e392-1714\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e267-4019\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e259-2647\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e260-468\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003eVND (m\u003csup\u003e-3\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.19-1.8x10\u003csup\u003e14\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e0.12-5.73x10\u003csup\u003e14\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.11-3.5x10\u003csup\u003e14\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e0.12-0.23x10\u003csup\u003e14\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"earth-planets-and-space","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"epsp","sideBox":"Learn more about [Earth, Planets and Space](http://earth-planets-space.springeropen.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/epsp/default.aspx","title":"Earth, Planets and Space","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Vulcanian, Phreatomagmatic, Stratigraphy, Componentry, Young Ciremai volcano.","lastPublishedDoi":"10.21203/rs.3.rs-5017130/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5017130/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Vulcanian eruptions, characterized by intermediate magma compositions, pose significant hazards due to their potential for both magmatic and phreatomagmatic fragmentation. The Young Ciremai volcano located in Indonesia has undergone recent phreatic-phreatomagmatic eruptions (from 1698 to 1951), with previous eruptions likely exhibiting both magmatic and phreatomagmatic fragmentations. In order to reconstruct the eruptive histories and elucidate the fragmentation mechanism, we integrate stratigraphic analysis, grain size distribution, componentry, bulk XRD analysis of fine ash, and petrographic analysis, which encompassed the morphometry, vesicularity, and crystallinity of ash particles. The results indicate a complex eruption history characterized by changing fragmentation mechanisms. Magmatic fragmentation correlates with the Vulcanian eruption style, which is characterized by diverse grain size distributions and higher vesicle number densities. The interactions between magma and water drive phreatomagmatic fragmentation, characterized by predominant finer ash exhibiting blocky textures and lower vesicle number densities. The eruptive evolution is described into three distinct stages: Stage 1 indicates magmatic fragmentation resulting from conduit plugging, Stage 2 signifies phreatomagmatic activity originating from the interaction with shallow groundwater, and Stage 3 emphasizes phreatic-hydrothermal activity with continuous recent solfatara manifestation. The results highlight the potential hazards of alternating magmatic and phreatomagmatic eruptions, including pyroclastic density currents and sudden phreatic explosions.","manuscriptTitle":"Transition from Magmatic to Phreatomagmatic Eruptions in Young Ciremai Volcano, Indonesia: Insights from Stratigraphy, Componentry, and Textural Analysis of Tephra Deposits","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-13 16:27:44","doi":"10.21203/rs.3.rs-5017130/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-12-12T06:00:01+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-12-12T05:39:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-12-12T04:56:37+00:00","index":"","fulltext":""},{"type":"submitted","content":"Earth, Planets and Space","date":"2024-12-11T08:55:23+00:00","index":"","fulltext":""},{"type":"decision","content":"Minor Revision","date":"2024-09-17T20:51:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"earth-planets-and-space","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"epsp","sideBox":"Learn more about [Earth, Planets and Space](http://earth-planets-space.springeropen.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/epsp/default.aspx","title":"Earth, Planets and Space","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b7d25eb2-1254-40aa-9871-9a79178fcbd0","owner":[],"postedDate":"December 13th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-02-17T16:04:08+00:00","versionOfRecord":{"articleIdentity":"rs-5017130","link":"https://doi.org/10.1186/s40623-025-02143-7","journal":{"identity":"earth-planets-and-space","isVorOnly":false,"title":"Earth, Planets and Space"},"publishedOn":"2025-02-14 15:57:58","publishedOnDateReadable":"February 14th, 2025"},"versionCreatedAt":"2024-12-13 16:27:44","video":"","vorDoi":"10.1186/s40623-025-02143-7","vorDoiUrl":"https://doi.org/10.1186/s40623-025-02143-7","workflowStages":[]},"version":"v1","identity":"rs-5017130","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5017130","identity":"rs-5017130","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}