Volcanic Conduit Research Articles

Inter-eruptive spatiotemporal variation of caldera contraction on Miyakejima volcano revealed by PALSAR and PALSAR-2 time-series data

Monitoring caldera deformation helps improve the understanding of pressure conditions within a volcanic conduit beneath the caldera. Miyakejima volcano in Japan experienced a caldera collapse associated with an eruption in 2000, which included dike intrusions. Although a previous InSAR study suggested deceleration of caldera subsidence in 2009, few observations on the caldera deformation have been reported. We applied SAR time-series analysis to Phased Array-type L-band Synthetic Aperture Radar (PALSAR) and PALSAR-2 data to investigate spatiotemporal variations of ground deformations at Miyakejima volcano during 2006–2011 and 2014–2019. The spatial characteristics of the caldera contraction transformed from a concentric pattern into a north-south asymmetric pattern in mid-2009, implying migration of a deformation peak from the central aspect to the southern edge of the caldera floor. These peaks of the caldera contraction are located at the initial position of the caldera collapse on the central caldera floor, and at an active fumarole on its southern edge. The asymmetric pattern of the caldera contraction continued during 2014–2019 based on PALSAR-2 data. Using the results of numerical modeling and earthquake distribution beneath the caldera, we interpreted that the continuous asymmetric caldera contraction was driven by brittle failures induced by continuous hydrothermal alterations. Although a previous study proposed deceleration of caldera subsidence in mid-2009, we believe that their findings revealed only a snapshot of the spatial variation of the caldera contraction detected in this study.

Mineralogical and geochemical investigations for subvolcanic hydrothermal alteration environments at an active volcano: An example of Hokkaido-Komagatake volcano, Japan

At active volcanoes, hydrothermal alteration related to subvolcanic hydrothermal systems can lead to volcanic hazards, such as edifice collapses and phreatic eruptions. Although it is difficult to investigate subsurface hydrothermally altered zones on active volcanoes directly because their edifices are rarely eroded, lithic materials derived from edifice interiors, such as debris avalanche deposits and phreatic ejecta, can contain information on subvolcanic hydrothermal zones and provide a way to investigate this. To reveal the hydrothermal system active during the historical eruptive stage of Hokkaido-Komagatake volcano, this study investigates the characteristics of hydrothermally altered lithic products in volcanic deposits and evaluates the hydrothermal environments using geochemical modeling. The debris avalanche deposits originally comprising the uppermost part of the edifice mainly contain smectite, kaolinite, and cristobalite, suggesting a low-temperature (approximately 100 °C) and weakly acidic to neutral environment. The deposits also have jarosite with a light-δ34S value which is formed from the oxidation of pyrite in a supergene environment, and the acid alteration induced by pyrite oxidation might weaken the edifice. Chlorite and mixed-layer chlorite/smectite comprise the altered rocks derived from the deeper part of the edifice, indicative of a higher temperature (150 to >200 °C) and nearly neutral environment at depth. Strongly acidic alteration, represented by alunite precipitation, is restricted to a fumarolic environment around the volcanic conduit, and this hydrothermal environment developed during the historical eruptive stage. Because the edifice mostly consists of permeable Plinian pumice and weakly welded tuff, the primary thermal water derived by the condensation of magmatic gas in groundwater flows while interacting with the edifice rocks, allowing meteoric water infiltration. Consequently, a relatively low-temperature and nearly neutral environment prevails in the edifice. This is consistent with the absence of acidic, SO4-rich thermal water in the crater area, and low-temperature and nearly neutral pH thermal waters discharge at the foot of the volcano. One of these waters showed heating and increased chemical concentrations related to an increase in magmatic gas flux. This thermal water is assumed to be derived from magmatic gas without scrubbing by the hydrothermal system. As a result, changes in magmatic gas flux directly affect the thermal and chemical changes in the thermal water. Thus, this thermal water can be an efficient monitoring tool for understanding volcanic activity of the volcano.

Lithofacies characteristics and controlling on volcanic reservoirs in the basement: A case study of the offshore Bohai Bay Basin, Eastern China

Volcanic rocks are important, but special reservoirs, for hydrocarbon exploration. Volcanic lithofacies play an important role in reservoir development, but the understanding of the relationship between lithofacies and reservoirs is still limited, especially for volcanic basements. In this paper, we characterized the intermediate-basic lithofacies features and discuss the relationship between lithofacies and reservoirs in the offshore Bohai Bay Basin. The results show that there developed volcanic conduit, eruptive (basic and neutral), explosive, and volcanogenic sedimentary facies in the study area. Among them, the explosive and eruptive facies are dominant. Different lithofacies present diverse well-logging and seismic responses, and the basic-eruptive (basalt), neutral-eruptive (andesite), explosive, and volcanogenic sedimentary facies are distributed from the bottom to top orderly fashion. This vertical superposition pattern represents a volcanic eruption process that has resulted in eruptive facies being more developed than explosive facies. The pores (intershard, dissolution, and devitrified pores) and tectonic fractures are the predominant spaces for explosive and neutral-eruptive facies (andesite), respectively. The lithofacies control the development of the primary spaces, fractures, and the diagenesis processes, leading to explosive and neutral-eruptive facies being the dominant facies for reservoir development. The understanding of high-quality reservoirs in the volcanic buried hills is not only controlled by weathering but also dominant lithofacies that will guide the volcanic exploration globally.

Influence of hydrothermal recharge on the evolution of eruption styles and hazards during the 2018\u20132019 activity at Kuchinoerabujima Volcano, Japan

The activity of the 2018–2019 eruption of Kuchinoerabujima Volcano in Japan changed from continuous ejection of ash-laden plumes between October 21 and the middle of December, to intermittent explosive activity accompanied by several pyroclastic density currents until January 2019. To understand the behaviors of magma and hydrothermal fluid that controlled the eruptive sequence, we carried out component analysis, X-ray diffractometry, and leachate analysis for ash samples. The proportion of non-altered volcanic ash particles is ~ 15% in the earlier phase, then it decreased to less than 10% in the later explosive phase. Accordingly, the mineral assemblage of the volcanic ash samples changed from plagioclase-dominant to sulfate minerals-dominant. Concentration of SO42− and Cl/SO4 values of the ash-leachates decreased toward the later activity. These results indicate that the proportion of fresh volcanic rocks decreased and sulfuric acid fluid-derived sulfate minerals increased toward the later activities. Consequently, the 2018–2019 eruption at Kuchinoerabujima Volcano changed from magmatic activity to phreatomagmatic activity. Weak glowing of the crater was observed during the magmatic activity, indicating the volcanic conduit was hot enough to dry up the sub-volcanic hydrothermal system. The following phreatomagmatic activity indicates that the hydrothermal fluid recharged after the magmatic eruption phase. Recharge of the hydrothermal fluid likely caused the variation of the eruption style, and is a process that may control the evolution of hazards during future eruption scenarios at similar active volcanoes in Japan and worldwide.Graphical

The diagnostic criteria of borehole electrical imaging log for volcanic reservoir interpretation: An example from the Yingcheng Formation in the Xujiaweizi Depression, Songliao Basin, China

Electrical image log can be used to establish volcanic facies sequences, and thus used for reservoir interpretation, while the key is to set up available diagnostic criteria to guide lithology, structure and facies interpretation. A total of 50 datasets of borehole image logs, combined with wireline logs and cores, have been collected in the Yingcheng volcanic reservoir in the Xujiaweizi Depression, Songliao Basin, providing an opportunity for repeated image interpretation in the volcanic strata. The interpreted lithology includes rhyolite, dacite, andesite, basalt, welded ignimbrite, tuff, volcanic breccia and agglomerate, sedimentary tuff, sedimentary volcanic breccia and agglomerate. The volcanic structures are calibrated in terms of fluidal and deformed fluidal structure, vesicular and amygdaloidal structure, and massive structure. Based on the lithology and structures, volcanic facies including volcanic sedimentary facies, effusive facies, explosive facies and volcanic conduit facies, have been further determined. Layered structures of the weathered volcanic crusts are shown in borehole images and mainly developed at the top of the Yingcheng Formation. Borehole images indicate that SHmax direction in the area is consistent with the regional SHmax direction, with a preferable trending of 88°. Four sets of filled/open tectonic fractures are developed with approximately north, south, NNE and NW dipping. It infers that different volcanic facies can be well correlated between wells, and tectonic movements have a slight influence on the Yingcheng volcanic strata. The proposed diagnostic criteria and the workflow can be referred for a direct image interpretation in volcanic reservoirs or ocean drilling programs when cores are unavailable.

The Role of Tuffs in Sealing Volcanic Conduits

AbstractAcid‐sulphate alteration commonly changes the physicochemical properties of volcanic conduits. Although several conduit pressurization models suggest hydrothermal sealing, little experimental evidence exists from conduit‐filling rocks on the development of such a seal. Here we show that acid‐sulphate alteration affects conduit‐filling lavas and tuffs differently, with implications for their role in sealing the conduit. In lavas, alteration creates fluid pathways and decreases rock stiffness by dissolving primary minerals. In contrast, in the inherently porous tuffs, alteration reduces fluid pathways and increases rock stiffness by precipitating secondary minerals. Compaction of tuffs under subsurface pressures together with such alteration‐related sealing can form low porosity and low permeability zones within the conduit. Such zones could promote fluid‐pressure build‐up and predispose the volcano to explosive eruptions. We discuss our results in the context of observed seismicity and ground deformation and suggest using our elastic properties data to constrain geophysical inversions of acid‐sulphate altered volcanic conduits.

Kinetic partitioning of major and trace cations between clinopyroxene and phonotephritic melt under convective stirring conditions: New insights into clinopyroxene sector zoning and concentric zoning

Within subvolcanic plumbing systems, along volcanic conduits and post-eruptive emplacement, mineral textures and compositions are governed by complex kinetic (undercooling) and dynamic (convective) processes that deviate from theoretical models and equilibrium criteria. In this perspective, we have investigated the partitioning of major and trace cations between clinopyroxene and phonotephritic melt under convective stirring conditions at high degrees of undercooling (−ΔTnominal = 30–60 °C) and atmospheric pressure. We have integrated this novel data set with conventional static (no physical perturbation) clinopyroxene-melt compositions obtained under interface- and diffusion-controlled growth regimes. Results show that clinopyroxene growth kinetics and diffusion boundary layers caused by melt supersaturation are partly mitigated by the homogenizing effects of stirring. Because of continuous supply of fresh melt to the advancing crystal surface, the partitioning of major and trace cations is governed by local equilibrium effects, which are interpreted as the extension of equilibrium thermodynamic principles to non-equilibrium bulk systems. Major cations are incorporated into the clinopyroxene structure via the coupled substitution [M1Mg, TSi] ↔ [M1Ti, TAl] and in conformity with the thermodynamic mixing properties of CaMgSiO2, CaAl2SiO6, and CaTiAl2O6 components. The complementary relationship between lattice strain (ΔGstrain) and electrostatic (ΔGelectrostatic) energies of heterovalent substitutions is the most appropriate thermodynamic description for the accommodation of trace cations in the clinopyroxene lattice site (i.e., ΔGpartitioning = ΔGstrain + ΔGelectrostatic). The excess energy of partitioning ΔGpartitioning changes principally with Al in tetrahedral coordination and determines the type and number of charge-balanced and -imbalanced configurations taking place in the structural sites of clinopyroxene. An important outcome from dynamic stirring experiments is that superimposition of convective mass transfer on melt supersaturation phenomena causes the formation of Cr-rich concentric zones under closed system crystallization conditions. However, these Cr-rich zones do not correlate with enrichment in other compatible elements and depletion in incompatible elements, as would be expected in natural open systems characterized by input of more primitive magmas. While the convective transport acts to reduce the diffusive length scale of chemical species in the experimental melt, fresh Cr cations are more easily incorporated into the concentric zones due to crystal field effects. Together, our findings reveal that during magma ascent and emplacement, convective stirring may promote clinopyroxene crystallization and minimize kinetic effects on clinopyroxene zoning.

Induced Polarization as a Tool to Assess Alteration in Geothermal Systems: A Review

The mineral alteration patterns in high- to low-temperature geothermal fields affect the induced polarization (electrical conductivity and chargeability) properties of volcanic rocks. Indeed, these properties are sensitive to the cation exchange capacity and the porosity of the rock, which are both dependent on the alteration path, temperature, and depth of burial. Therefore induced polarization tomography appears as a powerful non-intrusive geophysical method to investigate alteration patterns in geothermal fields. Among clay minerals, the production of smectite through prograde reactions occurs progressively in volcanic rocks up to 220 °C. The presence of smectite dominates the induced polarization response of the volcanic rocks because of its very large cation exchange capacity. It follows that induced polarization can be used as a non-intrusive temperature proxy up to 220 °C for both active and inactive geothermal fields, recording the highest temperatures reached in the past. The influence of magnetite and pyrite, two semi-conductors, also has a strong influence regarding the induced polarization properties of volcanic rocks. Various field examples are discussed to show how induced polarization can be used to image volcanic conduits and smectite-rich clay caps in volcanic areas for both stratovolcanoes and shield volcanoes.

Interactions Between Gas Slug Ascent and Exchange Flow in the Conduit of Persistently Active Volcanoes

AbstractMany volcanoes around the world are persistently active with continuous degassing for years or even centuries, sometimes exceeding historic records. Such long‐term stability contrasts with short‐term instability, reflected in eruptive episodes that punctuate passive degassing. These two aspects of persistent activity, long‐term stability as opposed to short‐term instability, are often conceptualized through two distinct model frameworks: Exchange‐flow in volcanic conduits is commonly invoked to explain the long‐term thermal balance and sustained passive degassing, while the ascent of large gas slugs is called upon to understand explosive eruptions. While typically considered separately, we propose here that both flow processes could occur jointly in the conduits of persistently active volcanoes and in transient connections between subvolcanic melt lenses. To understand the dynamic interplay between exchange flow and slug ascent, we link analogue laboratory experiments with direct numerical simulations. We find that the two flows superimpose without creating major disruptions when only considering the ascent of a single gas slug. However, the sequential ascent of multiple gas slugs is disruptive to the ambient exchange flow, because it may entail continual buildup of buoyant magma at depth. While our study focuses on the laboratory scale, we propose that the dependence of exchange‐flow stability on sequential slug ascent is relevant for understanding why explosive sequences are sometimes followed by effusive eruptions. Taken together, our work suggests that integrating exchange flow and slug ascent could provide a more complete understanding of persistently active volcanoes than either model framework offers in isolation.

Stress‐Driven Failure of Cylindrical Volcanic Conduits

AbstractMany explosive volcanic eruption sequences are characterized by exceedingly unsteady behavior, often punctuated by multiple explosive phases, separated by hours to days. What causes this unsteady behavior is not fully understood. Here, we explore one possible mechanism: stress‐driven failure of the volcanic conduit wall rock. We present a multiphase conduit flow model that predicts the shear and normal tractions exerted on the conduit wall, and couple (one way) these tractions with a numerical model of host rock failure. While analytical estimations of host rock stress serve as useful guides, analytical approximations which ignore shear tractions are insufficient to adequately predict conduit instability. Failure generally initiates near the fragmentation depth, where shear tractions are highest and magma pressure is low relative to the lithostatic stress. Shear tractions on the conduit wall, caused by viscous drag, promote strain localization and failure. The in situ stress state not only determines the range of conduit pressures which promotes failure, but also influences the style of failure. The mechanism that is most likely to lead to the disruption of flow, where wall rock moves radially into the conduit along normal faults, occurs in extensional stress regimes when large shear tractions at the fragmentation depth enhance normal fault formation. The results of this study indicate that conduit stability strongly depends on the ambient stress field and the nature of conduit flow at the fragmentation depth.

Characteristics and implications of Albian volcanism in a magma-rich rift basin: Seismic volcano stratigraphic and geomorphological evidence from the Upper Suhongtu Member in the Chagan Sag, China-Mongolia border region

Buried volcanic successions imaged by 3D seismic data reveal facies components of Albian volcanism in the Chagan Sag of the Yingen-Ejinaqi Basin. The volcanic rocks of the Upper Suhongtu Member are composed mainly of vesicular and tight massive basalts and andesites. Three types of volcanoes, including monogenetic volcanoes, flood basalts, and shield volcanoes were recognized through detailed seismic facies analysis. A seismic geomorphological study showed that volcanism declined from Unit 1 to Unit 2, with the decline being strongly associated with the transition from the rift climax to the later syn-rift phase. In Unit 1, a center-type eruption arose at the onset, and was subsequently overwhelmed by multistage basaltic lavas supplied by fissure vents of the Maoxi, Tulage, and Barun faults in response to increased thermal fluid activity. Several cone- and crater-shaped monogenetic volcanoes formed by the center-type eruption that developed in Unit 2. In addition, a large shield volcano supplied by fissure vents and a major volcanic conduit developed in the northwestern part. The Albian volcanism of the Yingen-Ejinaqi Basin and the whole volcanic province contributed to a much hotter and more arid paleoclimate, and their records can be recognized from palynological and elemental geochemical evidence in the Chagan Sag and its surrounding area. Volcanism not only produced widely distributed strongly heterogeneous volcanic reservoirs but also accelerated the thermal maturation of source rocks, contributing to near-source hydrocarbon accumulation in Lower Cretaceous magmatic-rich rift basins of the East Asian region.

Comparison of Bubble Shape Model Results With Textural Analysis: Implications for the Velocity Profile Across a Volcanic Conduit

AbstractTube pumice, which is characterized by aligned elongated bubbles, is valuable for our understanding of the shear field in a volcanic conduit. Most previous studies interpreted that tube pumice forms through simple shear, assuming a parabolic velocity profile across a volcanic conduit. However, simple shear cannot account for the observation that tube pumice is rare in plinian fall deposits but frequent in ignimbrites at the Taupō volcano, if the pyroclastic flows that formed them erupted through a wider vent and had a lower average shear rate. Here, we analyze the dynamics of bubble deformation that occurred during the 232 CE Taupō eruption by combining a bubble deformation model with a conduit flow model. The results indicate that bubble deformation is largely controlled by the velocity profile across a conduit. If the conduit flow has a parabolic velocity profile, the amount of bubble elongation is unrealistic compared to the Taupō fall deposits. It is more likely that the conduit flow has a plug‐like velocity profile due to viscous heating. We numerically confirmed that bubbles in the plug‐like flow are subject mainly to pure shear and accumulate less strain for elongation. We also calculated a viscous heating flow of the ignimbrite phase. We modeled a wider conduit, which suppresses viscous heating around the conduit walls and causes a higher proportion of the conduit to experience parabolic flow, compared to the plinian phase. The increased proportion of a parabolic profile may explain the high frequency of elongated bubbles in the ignimbrite phase pumice.

Multi-Parametric Field Experiment Links Explosive Activity and Persistent Degassing at Stromboli

Visually unattainable magmatic processes in volcanic conduits, such as degassing, are closely linked to eruptive styles at the surface, but their roles are not completely identified and understood. To gain insights, a multi-parametric experiment at Stromboli volcano (Aeolian Islands, Italy) was installed in July 2016 focusing on the normal explosive activity and persistent degassing. During this experiment, gas-dominated (type 0) and particle-loaded (type 1) explosions, already defined by other studies, were clearly identified. A FLIR thermal camera, an Ultra-Violet SO₂ camera and a scanning Differential Optical Absorption Spectroscopy were deployed to record pyroclast and SO2 masses emitted during individual explosions, as well as persistent SO₂ fluxes, respectively. An ASHER instrument was also deployed in order to collect ash fallouts and to measure the grain size distribution of the samples. SO2 measurements confirm that persistent degassing was far greater than that emitted during the explosions. Further, we found that the data could be characterized by two periods. In the first period (25–27 July), activity was mainly characterized by type 0 explosions, characterized by high velocity jets. Pyroclast mass fluxes were relatively low (280 kg/event on average), while persistent SO2 fluxes were high (274 t/d on average). In the second period (29–30 July), activity was mainly characterized by type 1 explosions, characterized by low velocity jets. Pyroclast mass fluxes were almost ten times higher (2,400 kg/event on average), while persistent gas fluxes were significantly lower (82 t/d on average). Ash characterization also indicates that type 0 explosions fragments were characterized by a larger proportion of non-juvenile material compared to type 1 explosions fragments. This week-long field experiment suggests that, at least within short time periods, Stromboli’s type 1 explosions can be associated with low levels of degassing and the mass of particles accompanying such explosive events depends on the volume of a degassed magma cap sitting at the head of the magma column. This could make the classic particle-loaded explosions of Stromboli an aside from the true eruptive state of the volcano. Instead, gas-dominated explosions can be associated with high levels of degassing and are indicative of a highly charged (with gas) system. We thus suggest that relatively deep magmatic processes, such as persistent degassing and slug formation can rapidly influence the superficial behavior of the eruptive conduit, modulating the presence or absence of degassed magma at the explosion/fragmentation level.

Repeating Earthquakes During Multiple Phases of Unrest and Eruption at Mount Agung, Bali, Indonesia, 2017

In 2017, Mount Agung produced a small (VEI 2) eruption that was preceded by an energetic volcano-tectonic (VT) swarm (>800 earthquakes per day up to M4.9) and two months of declining activity. The period of decreased seismic activity complicated forecasting efforts for scientists monitoring the volcano. We examine the time history of earthquake families at Mount Agung in search of additional insight into the temporal changes in the shallow crust prior to eruption. Specifically, we analyze the period of declining seismic activity about five weeks prior to the eruption when forecasting uncertainty was greatest. We use REDPy (Hotovec-Ellis and Jeffries, 2016) to build a catalog of 6,508 earthquakes from 18 October 2017–15 February 2018 and group them into families of repeating earthquakes based on waveform similarity using a cross-correlation coefficient threshold of 0.8. We show that the evolution of earthquake families provides evidence that Mount Agung was progressing toward eruption even though overall earthquake rates and seismic-energy-release declined. We find that earthquake families that dominated seismicity during the beginning of the crisis ceased near the onset of tremor on 12 November 2017. Then, earthquake families took on characteristics commonly observed during effusive phases of eruptions on 15 November—a full six days before the first phreatomagmatic eruption on 21 November 2017 and a full ten days before the actual onset of lava effusion on 25 November 2017. We interpret the transitions in seismicity as the manifestation of a three-phase physical model including an Intrusion Phase, a Transition Phase, and a Eruptive Phase. During the Intrusion Phase, seismicity was dominated by VT earthquakes with a relatively high percentage of repeaters (59%) grouped into numerous (65) simultaneous families. During the Eruptive Phase, seismicity included both VT and low frequency earthquakes that grouped into relatively long-lived families despite a low overall percentage of repeaters (14%). The Transition Phase exhibited characteristics of earthquake families between the Intrusion Phase and Eruptive Phase. We conclude that the time history of earthquake families provides insight into the evolution of the stress distribution in the volcanic edifice, the development of the volcanic conduit, and seismogenesis of magma effusion. Finally, we discuss the role that repeating earthquakes could play in real-time monitoring at restless volcanoes. Our work suggests eruption forecasts can be improved by incorporating automatic processing codes to assist seismologists during sustained periods of high earthquake rates, even at sparsely monitored volcanoes.

Obsidian pyroclasts in the Yellowstone-Snake River Plain ignimbrites are dominantly juvenile in origin

Dense, glassy pyroclasts found in products of explosive eruptions are commonly employed to investigate volcanic conduit processes through measurement of their volatile inventories. This approach rests upon the tacit assumption that the obsidian clasts are juvenile, that is, genetically related to the erupting magma. Pyroclastic deposits within the Yellowstone-Snake River Plain province almost without exception contain dense, glassy clasts, previously interpreted as hyaloclastite, while other lithologies, including crystallised rhyolite, are extremely rare. We investigate the origin of these dense, glassy clasts from a coupled geochemical and textural perspective combining literature data and case studies from Cougar Point Tuff XIII, Wolverine Creek Tuff, and Mesa Falls Tuff spanning 10 My of silicic volcanism. These results indicate that the trace elemental compositions of the dense glasses mostly overlap with the vesiculated component of each deposit, while being distinct from nearby units, thus indicating that dense glasses are juvenile. Textural complexity of the dense clasts varies across our examples. Cougar Point Tuff XIII contains a remarkable diversity of clast appearances with the same glass composition including obsidian-within-obsidian clasts. Mesa Falls Tuff contains clasts with the same glass compositions but with stark variations in phenocryst content (0 to 45%). Cumulatively, our results support a model where most dense, glassy clasts reflect conduit material that passed through multiple cycles of fracturing and sintering with concurrent mixing of glass and various crystal components. This is in contrast to previous interpretations of these clasts as entrained hyaloclastite and relaxes the requirement for water-magma interaction within the eruptive centres of the Yellowstone-Snake River Plain province.

Lake-level variation of Dali Lake in mid-east of inner Mongolia since the Late Holocene

In recent years, the area of Dali Lake has shrunk significantly, resulting in extremely serious ecological and environmental problems. Combining records from lake sediments and ancient shorelines is effective for investigating paleolake evolution and predicating the lake life trend. This study explored the lake area evolution of Dali Lake using remote sensing images and optical stimulated luminescence (OSL) dating. The results suggest the following: 1) on the century time scale, there has been a significant linear relationship between age and elevation from ca. 1.8 cal ka BP to the present (R2 = 0.99) and a potential quadratic polynomial relationship since ca. 4.2 cal ka BP (R2 = 0.99). 2) According to the δ2H and δ18O composition, monthly changes in the lake area, and water balance analysis, the groundwater was the main water source to recharge Dali Lake which originated from an external source, whereby the water may be from the Xar Moron Fault or has been transported by a volcanic conduit. 3) Since ca. 1.3 cal ka BP, the clear differences between lake levels and local precipitation indicated that the changes of the lake level are predominantly determined by groundwater. We conclude that the East Asian summer monsoon intensity and groundwater table variations in this area have jointly controlled the lake level evolution since the late Holocene.

The morphology and texture of Plinian pyroclasts reflect their lateral sourcing in the conduit

We investigated the relationships between the size, shape, density and texture of thousands of juvenile pyroclasts from the Plinian phase of the 1060 CE Glass Mountain eruption of Medicine Lake Volcano (California, USA). Analyzed pyroclasts, which originate from representative beds of both proximal and medial deposits, range from 0.125 mm to several centimeters in diameter. We show that the size, shape, density and texture of juvenile Plinian pyroclasts are intimately interrelated: as the size of pyroclast decreases from 64 mm to 0.125 mm, their shape shifts from equant to tabular to elongate. Moreover, while rounded vesicles dominate the largest clasts, elongate and distorted vesicles become progressively more present with decreasing clast size. Concurrently, clast density continually increases in a sigmoidal way from ∼0.4 gcm−3 (>80% porous) in the largest clasts to ∼1.7–1.9 gcm−3 (20–30% porous) by 0.125 mm. These observations are identical for both the proximal and medial locations. We show that expansion, compaction and secondary fragmentation did not significantly change the texture of juvenile pyroclasts after fragmentation. The size dependency of density and texture of Plinian pyroclasts is instead interpreted to originate from the lateral position of the magma in the conduit prior to fragmentation: smaller clasts result from higher shearing closer to conduit walls, where greater shear stresses increasingly elongate vesicles and fragment particles in smaller pieces. Moreover, ∼5% of pyroclasts 1–8 mm in size are likely agglomerates of mono-texture ash particles that sintered within the conduit during or shortly after primary fragmentation. Our work shows that future studies should analyze the full spectrum of clast sizes, from the micron- to centimeter-scale, in order to fully capture the complexity and breadth of eruptive processes across the volcanic conduit.

Microscale textural heterogeneity and tip-streaming instability in alkaline magmas: Evidence in tube pumices from Campi Flegrei, Italy

We present a textural investigation of compositionally homogeneous alkaline tube pumices from the plinian fallouts of the Agnano Monte Spina eruption (ca. 4.1 ka), Campi Flegrei, Italy. The pumice clasts present strong textural complexity from hand specimen to microscopic scale of inspection. The clasts are characterized by large vesicle tubes that extend up to several millimetres along the clast main axis. They also exhibit small and elongated vesicles arranged in stretched bands around textural domains of larger, sub-spherical vesicles associated with pyroxene, feldspar, and biotite phenocrysts. Clasts, vesicle tubes, vesicle deformation, major axes of pyroxene phenocrysts and crystals with size ≤100 μm align in the same direction. In addition, we observe chains of gradually smaller stretched vesicles likely generated from break-up of a larger parent vesicle (i.e., tip-streaming phenomenon). We use image analysis to quantify the heterogeneity of vesicle sizes and shapes. Then, we deduce the Capillary number (Ca) of the each single vesicle, which represents the ratio between the deforming viscous stress on a bubble and the restoring stress supplied by surface tension, and obtain the spatial distribution of Ca values within pumice clasts. As Ca depends on strain-rate and viscosity, the spatial distribution of Ca values provides us with a snapshot of the sub-millimetre scale variation in magma strain-rate and rheology before fragmentation. Ca in highly stretched vesicles is close to values (0.45 to 0.6) required for bubble-breakup induced by tip-streaming. Instead, low Ca values (0.3 to 0.45) are calculated for large sub-spherical vesicles mostly distributed around phenocrysts. We suggest that sub-millimetre heterogeneities in vesicle sizes and shapes recorded in tube pumices are caused by a combination of tip-streaming, heterogeneous bubble nucleation and second-boiling processes prior to fragmentation. The heterogeneous spatial distribution of Ca values may be the result of local micrometric shear localisation and consequent deformation upon break-up experienced by magma while ascending in the conduit. This deformation suggests that a variation of magma strain-rate and viscosity occurred before fragmentation at the clast microscale and this is likely to affect magma dynamics and fragmentation. Our results claim for future experimental and numerical modelling studies that investigate and consider the effect of such micrometric heterogeneities on magma rheology and flow condition variations inside volcanic conduits.

Development of IoT-Based Volcano Early Warning System

Monitoring volcanic activity this is indispensable for both research and disaster mitigation strategies. Therefore, the presence of volcano monitoring allows the monitoring, data recording and early warning system of volcanic activity from a distance that is real time. Volcanic monitoring system aims to detect any changes in volcanic status. Temperature and humidity become parameters of increased magma activity. Concentration of gasses includes SO2 and CO2, indicates of the depth of magma in volcanic conduit. Magma movement also triggers the earthquake.The instrument that used in this research are temperature and humidity sensor DHT11, SO2 sensor TGS2602, CO2 sensor MG811, and vibration sensor ADXL345. Temperature and humidity sensors used DHT11 sensors that serve to detect temperature and humidity in the air. DHT11 sensors can detect temperature between 0-50°C and humidity between 20-90% RH. SO2 emissions were detected using TGS 2602 sensors that detects SO2 gas between 0-100 ppm. While CO2 gas emissions used MG811 sensors that detect the presence of CO2 gas between 350-10000 ppm. Furthermore, the vibrations were detected using a digital accelerometer ADXL345 that detects vibrations between 0.1-3200 Hz.Data from all sensors processed using arduino promini microcontroller and then sent to ESP8266. ESP8266 is a wifi module that serves as a microcontroller enhancement to connect to wifi and create TCP / IP protocol. This module is also used to create an IoT project so that it can be accessed at any time on the web service page. This system will be assembled solar cells as a source of power supply.

Tidal controls on the lithospheric thickness and topography of Io from magmatic segregation and volcanism modelling

Tidal heating is expected to impart significant, non-spherically-symmetric structure to Jupiter’s volcanic moon Io. A signature of spatially variable tidal heating is generally sought in observations of surface heat fluxes or volcanic activity, an exploration complicated by the transient nature of volcanic events. The thickness of the lithosphere is expected to change over much longer timescales, and so may provide a robust link between surface observations and the tidal heating distribution. To predict long-wavelength lithospheric thickness variations, we couple three-dimensional tidal heating calculations to a suite of one-dimensional models of magmatic segregation and volcanic eruption. We find that the lithospheric thickness could either be correlated with the radially integrated heating rate, or weakly anti-correlated. Lithospheric thickness is correlated with radially integrated heating rate if magmatic intrusions form at a constant rate in the lithosphere, but is weakly anti-correlated if intrusions form at a rate proportional to the flux through volcanic conduits. Utilising a simple isostasy model we show how variations in lithospheric thickness can predict long-wavelength topography. The relationship between lithospheric thickness and topography depends on the difference in chemical density between the lithosphere and mantle. Assuming that this difference is small, we find that long-wavelength topography anti-correlates with lithospheric thickness. These results will allow future observations to critically evaluate models for Io’s lithospheric structure, and enable their use in constraining the distribution of tidal heating.