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Volcanic eruptions affect land and humans globally. When a volcano erupts, tons of volcanic ash materials are ejected to the atmosphere and deposited on land. The hazard posed by volcanic ash is not limited to the area in proximity to the volcano, but can also affect a vast area. Ashes ejected from volcano’s affect people’s daily life and disrupts agricultural activities and damages crops. However, the positive outcome of this natural event is that it secures fertile soil for the future. This paper examines volcanic ash (tephra) from a soil security view-point, mainly its capability. This paper reviews the positive aspects of volcanic ash, which has a high capability to supply nutrients to plant, and can also sequester a large amount of carbon out of the atmosphere. We report some studies around the world, which evaluated soil organic carbon (SOC) accumulation since volcanic eruptions. The mechanisms of SOC protection in volcanic ash soil include organo-metallic complexes, chemical protection, and physical protection. Two case studies of volcanic ash from Mt. Talang and Sinabung in Sumatra, Indonesia showed the rapid accumulation of SOC through lichens and vascular plants. Volcanic ash plays an important role in the global carbon cycle and ensures soil security in volcanic regions of the world in terms of boosting its capability. However, there is also a human dimension, which does not go well with volcanic ash. Volcanic ash can severely destroy agricultural areas and farmers’ livelihoods. Connectivity and codification needs to ensure farming in the area to take into account of risk and build appropriate adaptation and resilient strategy.

High-resolution images of Mercury's surface from orbit reveal that many bright deposits within impact craters exhibit fresh-appearing, irregular, shallow, rimless depressions. The depressions, or hollows, range from tens of meters to a few kilometers across, and many have high-reflectance interiors and halos. The host rocks, which are associated with crater central peaks, peak rings, floors, and walls, are interpreted to have been excavated from depth by the crater-forming process. The most likely formation mechanisms for the hollows involve recent loss of volatiles through some combination of sublimation, space weathering, outgassing, or pyroclastic volcanism. These features support the inference that Mercury's interior contains higher abundances of volatile materials than predicted by most scenarios for the formation of the solar system's innermost planet.

Rima Bode is located on the central nearside of the Moon, with its rich volcanic landforms, which is considered an ideal region for studying lunar geological evolution. In this study, we systematically analyzed the geomorphological characteristics, composition, spatial thickness variations in basalts and pyroclastic deposits, thermophysical properties, and chronology of Rima Bode using the Kaguya Multiband (MI) data, Moon Mineralogy Mapper (M3) data, Terrain Camera (TC) data, and the CE-2 Microwave Radiometer (MRM) data. The main results are as follows. (1) The basalts can be categorized into three distinct units (Regions II, III, and IV), and the distribution range of pyroclastic deposits was redefined. Using the crater excavation technique, the deposit thicknesses were constrained to 4.3–51.9 m for pyroclastic deposits and 2.3–269.2 m for basalts, establishing a quantitative stratigraphic framework; (2) this study reveals that pyroclastic deposits exhibit abnormally brightness temperature (TB) behaviors, with slower diurnal TB change rates, indicating their high thermal inertia. (3) Chronological analysis indicated that volcanism lasted for ~0.38 Ga, with at least four distinct episodes of volcanic eruptions, suggesting complex magmatic processes and continued thermal activity within this region. These findings establish a comprehensive geological framework for the Rima Bode region, thereby deepening our understanding of its geological evolution.

Our new paleomagnetic data provide the timescale for the eruptive sequence of the 45 ka Shikotsu caldera-forming eruption of VEI 7. The duration of the entire sequence is estimated to be centuries, which is considerably longer than previously thought. The studied volcanic sequence, located at ~ 10 km from the caldera rim, includes five units of pyroclastic flow deposits (units B3, C1, C2, D, and E in ascending order) and an uppermost pyroclastic surge deposit (unit F2). The ash matrix samples of the pyroclastic deposits, predominantly composed of juvenile material, were collected into aluminum and plastic cubes, which were precisely oriented using an originally designed tool set. As a result, the obtained paleomagnetic directions have high precision parameters (k = 200–1400) and small 95% confidence intervals (α 95  = 2–4°). These paleomagnetic directions determined from the sequence of the six units demonstrate a curve of paleomagnetic secular variation, which has a total angular distance of 14.4 ± 4.1°. The observed distinguishable paleomagnetic directions indicate that the earlier four units (B3, C1, C2, and D) were formed by four distinct eruptions over a period of 240 ± 70 years with repose times of decades between the eruptions. The indistinguishable paleomagnetic directions indicate that the three late-stage units (D, E, and F) were erupted in a short period, decades or less. Our new paleomagnetic data, combined with the reported petrological change in pumice, suggest that the extractions of crystal-poor rhyolitic melt from the magma chamber occurred in multiple eruptions over a considerable period (more than a hundred years). Graphical Abstract

Mountainous areas surrounding the Campanian Plain and the Somma-Vesuvius volcano (southern Italy) are among the most risky areas of Italy due to the repeated occurrence of rainfall-induced debris flows along ash-fall pyroclastic soil-mantled slopes. In this geomorphological framework, rainfall patterns, hydrological processes taking place within multi-layered ash-fall pyroclastic deposits and soil antecedent moisture status are the principal factors to be taken into account to assess triggering rainfall conditions and the related hazard. This paper presents the outcomes of an experimental study based on integrated analyses consisting of the reconstruction of physical models of landslides, in situ hydrological monitoring, and hydrological and slope stability modeling, carried out on four representative source areas of debris flows that occurred in May 1998 in the Sarno Mountain Range. The hydrological monitoring was carried out during 2011 using nests of tensiometers and Watermark pressure head sensors and also through a rainfall and air temperature recording station. Time series of measured pressure head were used to calibrate a hydrological numerical model of the pyroclastic soil mantle for 2011, which was re-run for a 12-year period beginning in 2000, given the availability of rainfall and air temperature monitoring data. Such an approach allowed us to reconstruct the regime of pressure head at a daily time scale for a long period, which is representative of about 11 hydrologic years with different meteorological conditions. Based on this simulated time series, average winter and summer hydrological conditions were chosen to carry out hydrological and stability modeling of sample slopes and to identify Intensity-Duration rainfall thresholds by a deterministic approach. Among principal results, the opposing winter and summer antecedent pressure head (soil moisture) conditions were found to exert a significant control on intensity and duration of rainfall triggering events. Going from winter to summer conditions requires a strong increase of intensity and/or duration to induce landslides. The results identify an approach to account for different hazard conditions related to seasonality of hydrological processes inside the ash-fall pyroclastic soil mantle. Moreover, they highlight another important factor of uncertainty that potentially affects rainfall thresholds triggering shallow landslides reconstructed by empirical approaches.

Mount Iriga is a small, dormant stratovolcano of basalt to basaltic andesite composition located in Luzon Island, Philippines. The volcanic edifice includes a well-preserved horseshoe-shaped avalanche scar 2 km across with an adjacent fan of hummocky debris avalanche deposit (DAD) formed by large-scale (1.5 km 3 ) gravitational edifice collapse. To constrain the age of the collapse and determine the character of volcanic activity that followed, we investigated and dated (using the 14 C accelerator mass spectrometry method) paleosoils and organic lake sediments as well as charcoal-containing pyroclastic deposits that closely pre- and post-dated emplacement of the DAD. We found that the collapse of Iriga occurred soon after its 1830 ± 40 BP explosive magmatic eruption (of St. Vincent type) that produced pyroclastic flows of scoriaceous basaltic andesite. In the avalanche-dammed Lake Buhi, the organic bottom sediments started to accumulate at 1780 ± 30 BP, marking the upper age limit of the DAD emplacement. The edifice collapse itself was not contemporaneous with any geologically detectable explosive eruption. After the collapse, a stubby block lava flow with volume of about 0.02 km 3 was extruded inside the horseshoe-shaped avalanche scar. The next eruption of Iriga, which was its only post-collapse explosive eruption, occurred at 1110 ± 30 BP. This phreatomagmatic eruption left a small steep-walled maar-like crater inside the broad avalanche scar in the vent area of the block lava flow. The extrusion of the block lava and the subsequent phreatomagmatic event were the only eruptions of Iriga that occurred after the edifice collapse. Together with the pre-collapse explosive eruption, they comprise the entire eruptive activity of Iriga during the Late Holocene and all occurred during the last 2000 years.

Mount Lawu was recorded to have erupted last on November 28, 1885, releasing volcanic material including magnetic minerals. The material settles in various places carried by the wind and river flow. The movement of wind and river flow is very influential in the process of transporting volcanic material. Large material directly falls around the mountain, usually in the form of large rocks, and undergoes physical and chemical weathering. Small-sized materials such as volcanic ash and small-mass rocks will be carried by the wind and river flows in all directions. However, the displacement does not remove the magnetic minerals contained in it. Magnetic minerals can be evaluated by the method of rock magnetism using MS. Bartington MS2 device with a dependent MS2B sensor by mass. From this tool, the low field susceptibility values in the range of 1467.5 x 10 −8 m 3 /Kg – 5262.1 x 10 −8 m 3 /Kg and high field susceptibility in the range of 1467,1 x 10 −8 m 3 /Kg. The volcanic material of Mount Lawu belongs to the Ilmenite (FeTiO3) group and belongs to the group of weak magnetism. Then further review the frequency-dependent susceptibility (%) to see the magnetic domains contained in the sample. From the magnetic susceptibility data, the percentage of frequency-dependent susceptibility (%) is less than 2%. From these data, the sample is not included in the superparamagnetic (SP) and in general the sample is classified as a multidomain item (MD).

A multiphase fluid dynamic model is used to explore the effects of entrainment of granular debris into sustained volcanic jets such as those which produce sub-Plinian to Plinian eruption columns. The debris may be sourced from processes such as avalanches from crater walls or from recycling of previously erupted material. The results indicate that debris is not immediately, homogeneously mixed into a jet but instead forms a dense sheath that is dragged upward around the jet margin. While very small volumes of debris relative to the eruptive discharge rate mix progressively into the jet with increasing altitude, the dense sheath can inhibit entrainment of air into the lower portions of the jet, which may explain signs of column instability such as increased stratification in fallout deposits where lithic content increases. As debris volume increases, the dense sheath can collapse from a range of elevations to feed pyroclastic currents. The presence of the sheath of entrained debris contradicts some assumptions such as the top-hat profile for density and velocity that is commonly used in 1-D models. Transitions from fallout-producing buoyant column to collapsing behavior can be related to debris entrainment without any changes in primary eruption parameters such as vent size, exit velocity, or gas content. Boiling-over behavior can also be caused by debris entrainment, including recycling of previously erupted material such as might occur in a crater with restricted outlet. When entrained debris is relatively fine-grained such that it can couple well with the erupting mixture, complex, highly transient overpressured jet processes can occur due to the pinching effect of debris flowing into the base of the jet. Increasingly coarse debris causes collimation of the jet within the sheath of entrained material. The results suggest that accounting for the effects of debris entrainment is likely important for theoretical assessment of many natural eruption sequences and for assessment of hazard scenarios for potential sub-Plinian to Plinian activity.

On the planet Mercury, pyroclastic deposits formed by explosive volcanism are developed around rimless volcanic pits that are up to dozens of kilometers in diameters. Some pyroclastic deposits on Mercury, however, host no discernable main eruption centers but feature pitted-ground terrains that each consists of many similar sized and irregularly shaped pits. Individual pits are usually much smaller and shallower than typical volcanoes on Mercury. The origin of these landforms is unknown, but it is indicative of styles of volcanism on Mercury and/or post-volcanic modifications. Here, we investigate the possible origin of these peculiar landforms based on their geological context, morphology, geometry, reflectance spectra, and geophysical background. Reflectance spectra of pyroclastic deposits around such volcanoes are comparable with those erupted from typical volcanic pits on Mercury, suggesting a genetic relation between these pitted-ground terrains with explosive volcanism, and the source magma might have similar compositions. Pitted-ground volcanoes are mainly observed in impact structures, and two cases were formed in high-reflectance smooth plains and channeled lava flows. Most pitted-ground volcanoes are relatively degraded compared with typical volcanoes on Mercury, and some might have been formed in geological recent times judged by both their pristine preservation and crosscutting relationship with impact rays. All pitted-ground volcanoes have unconfined morphology boundaries, and each case is composed by dozens of rimless pits that have similar preservation states and interconnected edges. Such morphological characteristics are unique among volcanic landforms on terrestrial bodies, and they cannot be explained by multiple post-eruption collapses of a main explosive volcano. Pitted-ground volcanoes that are developed in lava flows with the same age have different preservation states, suggesting that the pits were not formed by escape of thermally destabilized volatiles from substrate and subsequent roof collapses. The largest pitted-ground volcano (~3700 km2) is located on the Borealis Planitia, and Bouguer gravity data reveal no larger mass concentration in the subsurface than surrounding terrains, consistent with a paucity of shallow intrusions in the crust of Mercury. Short-term and spatially-clustered explosive eruptions could explain the peculiar morphology and geometry of the pits, suggesting that pits in a given pitted-ground volcano are akin to swarms of monogenetic volcanoes. However, possible magma dynamics for the formation of pitted-ground volcanoes cannot be confirmed until future high-resolution gravity mapping could reveal detailed interior structures beneath these volcanoes. Based on comparative studies with spatially-clustered and similarly aged volcanoes on Earth, we interpret that a combination of pervasive crustal fractures and regional thermal anomaly in the thin mantle of Mercury might have caused such short-term and spatially-clustered explosive eruptions. If this interpretation was true, the heavy degradation state of most pitted-ground volcanoes and the few well-preserved cases are consistent with an overall cooling trend of the mantle, indicating the existence of longstanding heterogeneous thermal structures in the mantle.

We have conducted spectral and spatial analysis of the Compton–Belkovich Thorium Anomaly (61.1°N, 99.5°E) region on the far side of the Moon based on high-resolution data from recent lunar missions. Chandrayaan-1 Moon Mineralogy Mapper data of Compton–Belkovich volcanic complex (CBVC) reveal the existence of a strong doublet feature near 2800 nm throughout the volcanic construct, which could be attributed to the presence of water and/or hydroxyl in the studied site. Very high resolution Lunar Reconnaissance Orbiter Camera–Narrow Angle Camera mosaic of the study area shows that the strongest of the hydration features within the CBVC is primarily related with either sunlit inner flanks of small-sized fresh craters or fresh escarpments associated with the central collapse structure. Moreover, Mini-RF Synthetic Aperture Radar data from Lunar Reconnaissance Orbiter mission suggests the presence of a thick pyroclastic deposit in the volcanic complex. Our study indicates that the enhanced hydration at CBVC could possibly have originated from the episodic events of eruption and effusion involving silicic magma, which could probably be responsible for the tapping of a zoned magma body with a water-rich cap. Morphology of CBVC also confirms the presence of episodic effusive and eruptive events that probably had led to the formation of elevated topography, central collapsed feature and late eruptive domes in the study area.