Landslides are one of the most hazardous geological processes due to their difficult-to-predict nature and destructive effects, often leading to significant loss of life, infrastructure damage, and environmental disruption. In the Southern Andes of Chile, landslides are particularly frequent and destructive due to a combination of factors, including high seismic activity, steep topography, and the presence of weak, unconsolidated pyroclastic soils. Unfortunately, the geomechanical control of landslide initiation in the Southern Andes is still poorly understood, creating a significant source of uncertainty in developing accurate landslide susceptibility or risk models. This study evaluates the geological and geotechnical factors that control the generation of landslides in pyroclastic soils using in situ data, laboratory analysis and remote sensing approaches. The study area covers the surroundings of the Mocho-Choshuenco Volcanic Complex (MCVC), one of the most explosive volcanoes in the Southern Andes. The results show that the landslides are placed on slopes covered by multiple explosive eruptions that include a period of more than 12 ka. Landslide activity is related to pyroclastic soils with significant weathering and halloysite content. In addition, the geotechnical characteristics show very light soils, with highwater retention capacity, which is vital to induce mechanical instability. The detected deformation may be associated with seasonal precipitation that would increase the pore water pressure and reduce the shear strength of the soil, promoting slow-moving landslides. The geological and geotechnical characteristics of the soils suggests that slow-moving landslides would be extended to a large part of the Southern Andes. Finally, this study contributes to improving hazard assessment to mitigate the impact of landslides on the population, infrastructures and natural resources in the Southern Andes.

We present a multidisciplinary research aimed at quantifying the conditional probabilities for hazards associated with pyroclastic avalanches at Etna, which combines physical and numerical modeling of granular avalanches and probabilistic analysis. Pyroclastic avalanches are modeled using the depth-averaged model IMEX-SfloW2D, which is able to simulate the transient propagation and emplacement of granular flows generated by the collapse of a prescribed volume of granular material. Preliminary sensitivity analysis allowed us to identify the main controlling parameters of the dynamics, i.e. the total avalanche mass, the initial position of the collapsing granular mass (and the associated terrain morphology), the initial avalanche velocity, and the two rheological parameters which determine the mechanical properties of the flow. While the first two parameters can be considered as scenario parameters in the definition of the hazards, the initial velocity and the rheological parameters need to be calibrated. We therefore adopted a methodology for the statistical calibration of the physical model parameters based on field observations. We used data from the pyroclastic avalanche that occurred on February 10, 2022 at Etna, for which we had an accurate mapping of the deposit and some estimates of the total mass and the initial volume. We then run a preliminary ensemble of numerical simulations, with fixed initial volume and position, to calibrate the other input parameters. Based on the accuracy of the matching of the simulated and observed deposits (measured by the Jaccard Index), we extracted from the simulation ensemble a subsample of equally probable combinations of initial velocities and rheological parameters. We then built an ensemble of model input parameters, with varying (i) avalanche volumes, (ii) initial positions, (iii) velocity, and (iv) rheological coefficients. The initial volume range was chosen within the range of observed pyroclastic avalanches at Etna (i.e., between 0.1 and 3 x 106 m3), using a prescribed probability distribution extracted from the literature data. The initial positions have been chosen on the flanks of the South East Crater of Etna, with homogeneous spatial distribution. The initial velocity and the rheological coefficients were chosen from the subsample created with the calibration. Finally, a semi-automatic procedure (digital workflow) running the Monte Carlo simulation allowed us to produce the first probabilistic map of pyroclastic avalanche invasion at Etna. Such a map, conditional to the occurrence of a pyroclastic avalanche event, can be used to identify the hazardous areas of the volcano and to plan mitigation measures.

Rainfall infiltration plays a crucial role in the near-surface response of soils, influencing other hydrological processes (such as surface and subsurface runoff, groundwater dynamics), and thus determining hydro-geomorphological risk assessment and the water resources management policies. In this study, we investigate the infiltration processes in pyroclastic soils of the Campania region, Southern Italy, by combining measured in situ data, physical laboratory model observations and a 3D physically based hydrological model. First, we validate the numerical model against the soil pore water pressure and soil moisture measured at several points in a small-scale flume of a layered pyroclastic deposit during an infiltration test. The objective is to (i) understand and reproduce the physical processes involved in infiltration in layered volcanoclastic slope and (ii) evaluate the ability of the model to reproduce the measured data and the observed subsurface flow patterns and saturation mechanism. Second, we setup the model on the real site where soil samples were collected and simulate the 3D hydrological response of the hillslope. The aim is to understand and model the dynamics of hydrological processes captured by the field observations and explain the redistribution of water in different layers during 2 years of precipitation. For both applications, a Monte Carlo analysis has been performed to account for the hydrological parameter uncertainty. Results show the capability of the model to reproduce the observations in both applications, with mean KGE of 0.84 and 0.68 for pressure and soil moisture data in the laboratory, and 0.83 and 0.55 in the real site. Our results are significant not only because they provide insight into understanding and simulating infiltration processes in layered pyroclastic slopes but also because they may provide the basis for improving geohazard assessment systems, which are expected to increase, especially in the context of a warming climate. Combining physical model and in situ measurements of soil water content and soil water pressure together with a 3D hydrological models, we detailed and disentangled the infiltrations processes trough layered pyroclastic soils. The finding will be relevant for accurate geo-hydro risk management in a changing climate. image

Air-fall pyroclastic soil deposits usually display a loose fabric composed of alternating layers of ashes and pumices. Such deposits, when lying on steep slopes, represent a major geohazard due to the occurrence of landslides. This is the case of the carbonate massifs in Campania (southern Italy), a wide landslide-prone area of approximately 400 km2 covered with pyroclastic soils. In such cohesionless deposits, the additional shear strength provided by soil suction in unsaturated conditions is important for ensuring slope stability and can be jeopardized by soil wetting during rainwater infiltration. This paper provides a comprehensive view of the hydraulic and shear strength characteristics of different layers of pyroclastic deposits at different sites in Campania, revealing a broad view of their similarities and differences. To that end, some datasets from previous studies and novel data are gathered, linking the index properties, the hydraulic behavior of the soils and the contribution of suction to the shear strength of the studied materials. Two types of ashes at different positions within the stratigraphic sequence are identified: ashes interbedded between pumice layers, where landslide failure surfaces usually occur, and altered ashes in contact with the bedrock, which affects water leakage from the overlying soil profile. The former show quite uniform characteristics, and this allowed testing some predictive models for the assessment of the unsaturated shear strength of pyroclastic ashes in the absence of direct measurements. In contrast, the latter may exhibit significantly different behaviors, with great variability in hydraulic and mechanical properties.

Lunar Pyroclastic Deposits (LPDs) are sites of explosive volcanism and often occur in areas of effusive volcanism on the Moon. On Earth, it has been observed that most volcanism has both effusive and explosive phases, whereas on the Moon, these two types of volcanism have typically been considered separately. We hypothesize that the relationship between explosive and effusive volcanism on the Moon is similar to what is observed on the Earth, where individual eruptions can experience multiple phases rather than one type of volcanism always preceding another or occurring separately. We present observations from the Moon Mineralogy Mapper detailing compositional relationships between volcanic features in the lunar Montes Apenninus region. We evaluated whether co-located LPDs and effusive features (e.g., rilles, mare) could have erupted from the same volcanic vent or even at the same time based on their compositional similarities and stratigraphic relationships. We found that the LPDs have varied stratigraphic relationships with co-located effusive features. We identified LPDs near sinuous rilles that may be related to the formation of the rille, where explosive and effusive volcanism occurred at the same vent (e.g., Mozart Rille), and LPDs that may be unrelated to the rille (e.g., Rimae Bode and Rima Bode LPD). Our results suggest that lunar volcanism can mirror terrestrial volcanism, with explosive and effusive eruptions demonstrating more complex dynamics and relationships than previously thought. This variability suggests that the relationship between LPDs and nearby volcanic features cannot be generalized for studies on their resource potential, eruption styles, or deposit volume.

The Tacquet Formation (TF) was first identified in geologic mapping of southern Mare Serenitatis as a distinct low albedo region split by the linear Rimae Menelaus rilles. A distinct western dome, split by a linear rille and less distinct eastern dome (the Menelaus domes) are also present within the TF. Previous Earth-based radar analyses showed that the TF has a lower circular polarization ratio consistent with a pyroclastic mantle. In this study, compositional and spectroscopic parameters were derived from Moon Mineralogy Mapper (M-3) data. Lunar Reconnaissance Orbiter Camera Wide Angle Camera (LROC WAC) and SELENE Kaguya Multiband Imager (MI) multispectral data were also utilized. FeO derived from MI data for the TF and Menelaus domes was elevated at levels consistent with pyroclastic glasses. While not diagnostic of pyroclastics, TiO2 derived from LROC WAC data over the TF and Menelaus domes was also elevated relative to the background materials. Analysis of 1 and 2 mu m band parameters also show the TF and Menelaus domes as being distinct with a band center moderately longer than 1 mu m and 2 mu m band center shorter than the surroundings, characteristics consistent with pyroclastic glass and/or increased ilmenite. M-3 data thermally corrected via two different thermal correction approaches indicate a moderately deeper band in the 3 mu m region indicative of OH and/or H2O, a characteristic that is also potentially associated with pyroclastic deposits. These compositional findings are consistent with the Earth-based radar data suggesting that the TF is a pyroclastic mantle and potentially represents a previously unrecognized sub-class of pyroclastic deposits associated with lunar volcanic domes.

The Moon is not volcanically active at present, therefore, we rely on data from lunar samples, remote sensing, and numerical modeling to understand past lunar volcanism. The role of different volatile species in propelling lunar magma ascent and eruption remains unclear. We adapt a terrestrial magma ascent model for lunar magma ascent, considering different compositions of picritic magmas and various abundances of H-2, H2O, and CO (measured and estimated) for these magmas. We also conduct a sensitivity analysis to investigate the relationship between selected input parameters (pre-eruptive pressure, temperature, conduit radius, and volatile content) and given outputs (exit gas volume fraction, velocity, pressure, and mass eruption rate). We find that, for the model simulations containing H2O and CO, CO was more significant than H2O in driving lunar magma ascent, for the range of volatile contents considered here. For the simulations containing H-2 and CO, H-2 had a similar or slightly greater control than CO on magma ascent dynamics. Our results showed that initial H-2 and CO content has a strong control on exit velocity and pressure, two factors that strongly influence the formation of an eruption plume, pyroclast ejection, and overall deposit morphology. Our results highlight the importance of (a) quantifying and determining the origin of CO, and (b) understanding the abundance of different H-species present within the lunar mantle. Quantifying the role of volatiles in driving lunar volcanism provides an important link between the interior volatile content of the Moon and the formation of volcanic deposits on the lunar surface.

Volcanic activity on Mars peaked during the Noachian and Hesperian periods but has continued since then in isolated locales. Elysium Planitia hosts numerous young, fissure-fed flood lavas with ages ranging from approximately 500 to 2.5 million years (Ma). We present evidence for a fine-grained unit that is atypical of aeolian deposits in the region and may be the youngest volcanic deposit yet documented on Mars. The unit has a low albedo, high thermal inertia, includes high-calcium pyroxene-rich material, and is distributed symmetrically around a segment of the Cerberus Fossae fissure system in Elysium Planitia. This deposit is superficially similar to features interpreted as pyroclastic deposits on the Moon and Mercury. Unlike previously documented lava flows in Elysium Planitia, this feature is morphologically consistent with a fissure-fed pyroclastic deposit, mantling the surrounding lava flows with a thickness on the order of tens of cm over most of the deposit and a volume of 1.1-2.8 x 10(7) m(3). Thickness and volume estimates are consistent with tephra deposits on Earth. Stratigraphic relationships indicate a relative age younger than the surrounding volcanic plains and the Zunil impact crater (similar to 0.1-1 Ma), with crater counting suggesting that the deposit has an absolute model age of 53 +/- 7 to 210 +/- 12 ka. This young age implies that if this deposit is volcanic then the Cerberus Fossae region may not be extinct and that Mars may still be volcanically active. This interpretation is consistent with the identification of seismicity in this region by the Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) lander, and has additional implications for astrobiology.

Lunar mare regolith is traditionally thought to have formed by impact bombardment of newly emplaced coherent solidified basaltic lava. We use new models for initial emplacement of basalt magma to predict and map out thicknesses, surface topographies and internal structures of the fresh lava flows, and pyroclastic deposits that form the lunar mare regolith parent rock, or protolith. The range of basaltic eruption types produce widely varying initial conditions for regolith protolith, including (1) autoregolith, a fragmental meter-thick surface deposit that forms upon eruption and mimics impact-generated regolith in physical properties, (2) lava flows with significant near-surface vesicularity and macroporosity, (3) magmatic foams, and (4) dense, vesicle-poor flows. Each protolith has important implications for the subsequent growth, maturation, and regional variability of regolith deposits, suggesting wide spatial variations in the properties and thickness of regolith of similar age. Regolith may thus provide key insights into mare basalt protolith and its mode of emplacement.

In a new era of lunar exploration, pyroclastic deposits have been identified as valuable targets for resource utilization and scientific inquiry. Little is understood about the geomechanical properties and the trafficability of the surface material in these areas, which is essential for successful mission planning and execution. Past incidents with rovers highlight the importance of reliable information about surface properties for future, particularly robotic, lunar mission concepts. Characteristics of 149 boulder tracks are measured in Lunar Reconnaissance Orbiter Narrow Angle Camera images and used to derive the bearing capacity of pyroclastic deposits and, for comparison, mare and highland regions from the surface down to similar to 5-m depth, as a measure of trafficability. Results are compared and complemented with bearing capacity values calculated from physical property data collected in situ during Apollo, Surveyor, and Lunokhod missions. Qualitative observations of tracks show no region-dependent differences, further suggesting similar geomechanical properties in the regions. Generally, bearing capacity increases with depth and decreases with higher slope gradients, independent of the type of region. At depths of 0.19 to 5m, pyroclastic materials have bearing capacities equal or higher than those of mare and highland material and, thus, may be equally trafficable at surface level. Calculated bearing capacities based on orbital observations are consistent with values derived using in situ data. Bearing capacity values are used to estimate wheel sinkage of rover concepts in pyroclastic deposits. This study's findings can be used in the context of traverse planning, rover design, and in situ extraction of lunar resources. Plain Language Summary Future explorers will be visiting pyroclastic deposits for research and resource extraction. However, the properties of the surface are not well known and it is unclear how well vehicles and humans are able to travel across these areas. Properties of 149 boulder tracks are measured in spacecraft imagery and are used to derive estimations for the strength of pyroclastic, mare, and highland area material from the surface down to similar to 5-m depth. Results are compared and complemented with soil strength estimates that have been derived based on in situ measurements taken during previous lunar surface missions. In all regions of interest, tracks have similar appearances, implying that the surface material has comparable properties. Generally, soil strength increases with increasing depth and decreases with higher local slope angles. At depth, pyroclastic deposits show equal or significantly higher strength in comparison to mare and highland areas and, therefore, might be equally trafficable at surface level. Calculations based on globally distributed spacecraft images agree with values derived from Apollo-era in situ data. Based on the soil strength, the sinkage of rovers in the areas of interest is estimated. Potential applications of this work include rover design and mission planning, infrastructure construction, and resource extraction.