After three foreshocks the day before (M5.0, M4.7 and M4.1, respectively), a strong M6.4 Petrinja earthquake occurred on December 29, 2020, followed by thousands of aftershocks (the strongest was a January 6 M5.0 earthquake). This paper presents a unique multihazard sequence of complex events resulting in numerous cover-collapse sinkhole failures. Although the area heavily impacted by the earthquake was larger than 1,000 km2, all 91 sinkholes appeared within a 4 km2 area surrounding Mečenčani and Borojevići villages located 20–25 km SE of the epicentral area, during the three months following the main earthquake. That area was also previously prone to seldom sinkhole appearances, as evidenced by 45 documented fossil sinkholes. All 91 sinkholes opened as post-seismic events; the first one (the second biggest, 10.8x9.8 m in diameter and 3.6 m deep) started to open six hours after the strongest earthquake. The biggest sinkhole, 25x23 m in diameter and 11.7 m deep, opened seven days after the main earthquake and one day before the strongest aftershock; its total volume is larger than volume of all other 90 new sinkholes combined. The Mečenčani and Borojevići villages surroundings is the only area where a 4–15 m thick sequence of Holocene soil built of unsaturated low plasticity clays with gravel and sand interlayers and lenses covers the heavily karstified carbonate bedrock composed of alternating highly porous Miocene limestones and calcarenites. The unconfined aquifer within a soil is underlain by a well-permeable confined karst aquifer in which the water pressure during wet periods becomes subartesian to artesian, enabling significant erosion and formation of numerous caverns at the soil–limestone contact. Continuous removal of eroded sediment by groundwater flow through karstified systems in carbonates gradually expands cavernous space until a final cover-collapse. The 2020–2021 Petrinja earthquake sequence significantly accelerated these processes, resulting in 91 cover-collapse sinkholes opened during a three-months period, instead of usually one sinkhole opened every few years as reported by local people. It is interesting to note that during the strongest earthquake the water level in the unconfined aquifer was very close to the surface, and in the underlying karst aquifer artesian conditions prevailed.

Pore pressure in aquifers confined below a cryosphere will increase as Mars cools and the cryosphere thickens. The increase in pore pressure decreases the effective stress and hence will promote seismicity. We calculate the rate of pore pressure change from cooling of the Martian interior and the modulation of pore pressure from solar and Phobos tides and barometric loading. Using the time-varying pressure and tidal stresses, we compute Coulomb stress changes and the expected seismicity rate from a rate-and-state friction model. Seismicity rate will vary by several 10s of percent to two orders of magnitude if the mean pore pressure is within 0.2 MPa and 0.01 MPa of lithostatic, respectively. Seismic events promoted by high pore pressure may be tremor-like. Documenting (or not) tidally-modulated shallow seismicity would provide evidence for (or against) water-filled confined aquifers, that pore pressure is high, and that the state of stress is close to failure — with implications for processes that can deliver of water to the Martian surface.

In this research, GRACE satellite data have been used in order to investigate the possibility of estimating the amount of groundwater used in agriculture. The level-2 data of the GRACE satellites have been used to estimate the monthly groundwater level changes in central plateau catchment in Iran during the period of 2003 to 2013. One degree grid is used along with corrections of soil moisture, canopy, rainfall and snowfall from GRACE satellite data with the CLM4 hydrology model. The results revealed the amount of current groundwater in Iran and agricultural usage from groundwater have been determined (the largest consumer of groundwaters). verification of the results has been done by comparing the GRACE satellite data and piezometric wells data. Furthermore, ArcMap (ArcGIS) software were used for data analysis.

Social scientists have a long history of documenting disasters and natural extreme events’ behavioural response through the collection of perishable post-event data (Gruntfest 1977; Quarantelli and Dynes, 1977; Stalling, 1987; Quarantelli, 1997, 2003; Drabeck, 1999). Such empirical and theoretical foundations constitute a strong background to understand crisis responses and advance our knowledge of the drivers of human behavioural responses to fast evolving weather-related events. Outputs from this field of research show that public warning and behavioural response is a social process that takes several phases before a protective action is put in place (Mileti, 1995; Trainor et al., 2008, Parker et al., 2009, Lindell et al., 2004). These authors identified factors related to the characteristics of the hazard, the warning information characteristics, the situational and personal characteristics of the receiver and the socio-cultural context as strong determinants of the public behavioural response. In fast-moving events like flash-floods, the amount of time available to detect the threat and respond to it is so limited that protective actions often consist in dealing with contingent situations triggered by the irruption of dangerous circumstances in the middle of daily life activities and routines (Ruin et al., 2008, 2009; Terti et al., 2015). Understanding how people actually detect potentially dangerous circumstances and manage to timely adapt their routine to cope with the speed of the hazard evolution remains a challenge. Based on insights from post-event interviews, online surveys were used to quantitatively document behavioural responses associated with 3 catastrophic flash flood events that happened in southern France in 2014 and 2015. The coupled analysis of responses to these surveys with hydrometeorological parameters allows to better understand the link between the event magnitude and self-protective behaviours in the context of short-fuse weather events as flash floods. Knowledge gained from such an integrated approach is necessary for drawing lessons for the development of coupled human-natural system modeling and the prediction of the human vulnerability dynamics in short-fuse weather events.

Changes in the quantity and quality of groundwater and water in the hydrological cycle in general have important implications for the evolution of water resources, the built environment, and terrestrial and aquatic ecosystems, globally. Exploitation of groundwater and other subsurface resources may lead to e.g. land subsidence, salt water intrusion, loss of important terrestrial and aquatic ecosystems and hence biodiversity. Together with biogeochemical flows of nitrogen and phosphorus and changes in the land-system and climate, these are currently considered the main environmental problems of the planet, which are breaching or close to breaching planetary boundaries. Changes in the hydrological cycle including groundwater is closely related to and affecting these changes. It is the ambition of the four GeoERA groundwater projects studying aspects of groundwater quantity and quality issues related to natural processes and human activities to further develop the European Geological Data Infrastructure as a leading information platform for groundwater data in Europe and one of the leading platforms, globally. Here we briefly present the contents and objectives of the four groundwater projects: HOVER - Hydrogeological processes and geological settings over Europe controlling dissolved geogenic and anthropogenic elements in groundwater of relevance to human health and the status of dependent ecosystems; RESOURCE - Resources of groundwater, harmonized at cross-border and Pan-European Scale; TACTIC – Tools for assessment of climate change impact on groundwater and adaptation strategies and VoGERA - Vulnerability of shallow groundwater resources to deep sub-surface energy-related activities. The four projects will deliver “FAIR” (Findable, Accesssible, Interoperable and Reusable) data and information via the European Geological Data Infrastructure easily accessible for all relevant endusers. This will improve our understanding of the subsurface and support common efforts for developing geoethical uses of the subsurface.

The Ethiopian sector of the East African Rift system (the Main Ethiopian Rift, MER) and Afar rift showcase advanced stages of continental breakup. Here the interplay between active continental rifting and rift-induced volcanism poses key questions regarding the mantle geodynamics of late-stage rift development. A particular subject of interest is the presence of hot mantle upwellings in the sub-rift mantle, which are inferred from geophysical imaging. Magma generation in the sub-rift asthenosphere depends on the temperature, lithology, and composition of the upwelling mantle material. Geophysical observations of the sub-rift mantle must therefore be supported by petrological studies aimed at understanding the physico-chemical conditions of melt production. In this study we investigate melt generation beneath the MER and Afar using a mantle melting model constrained by olivine crystallization temperatures and rare-earth element (REE) concentrations, both observed in rift zone lavas. Olivine crystallization, a proxy for magma liquidus temperature, is directly related to the thermodynamic and geochemical conditions of the melting mantle. Through application of an olivine-spinel aluminium exchange thermometer, we provide the first petrological olivine crystallization temperatures for MER and Afar basalts (1177±16°C and 1263±43°C respectively). A multi-lithology mantle melting model subsequently allows for inversion of our olivine crystallization temperatures and observed REE concentrations of rift magmas to estimate the temperature, lithology, and composition of the Ethiopian mantle. Our results suggest that the crystallization temperatures and REE distributions measured at the MER and Afar necessitate elevated mantle temperatures (Tp ≥ 1450 °C) relative to ambient mid-ocean ridge mantle. A thick mantle lithosphere (~60 km) is also required to provide deep garnet-field mantle melting inferred from REE distributions. We additionally conclude that an enriched and fusible pyroxenitic mantle component is necessary to match crustal melt thicknesses and observed REE concentrations. The composition of this pyroxenitic lithology is further explored through our inversions, and the contributions of enriched pyroxenitic melts to rift volcanism in the MER and Afar are subsequently compared.

Maar-diatremes are inverted conical structures formed by subterranean excavation and remobilization of country rocks during explosive volcanism and common in mafic volcanic fields. We focus on impacts of excavation and filling of maar-diatremes on the local state of stress, and its subsequent influence on underlying feeder dikes, which are critical for understanding the development of intrusive networks that feed surface eruptions. We address this issue using finite element models in COMSOL Multiphysics®. Inverted conical structures of varying sizes are excavated in a gravitationally loaded elastic half-space, and then progressively filled with volcaniclastic material, resulting in changes in the orientations and magnitudes of stresses generated within surrounding rocks and within the filling portion of the maar-diatreme. Our results show that rapid unloading during maar-diatreme excavation generates a horizontal compressive stress state beneath diatremes. These stresses allow magma to divert laterally as saucer-shaped sills and circumferential dikes at varying depths in the shallow feeder system, and produce intrusion geometries consistent with both field observations from exhumed volcanic fields and conceptual models of diatreme growth. Stresses generated in these models also provide an explanation for the evolving locations of fragmentation zones over the course of diatreme’s filling. In particular, results from this study suggest that: (1) extensional stresses at the base of the diatreme fill favor magma ascent in the lower half of the structure, and possibly promote volatile exsolution and magma fragmentation; and (2) increased filling of diatremes creates a shallow compressive stress state that can inhibit magma ascent to the surface, promoting widespread intra-diatreme explosions, efficient mixing of host rock, and upward widening of the diatreme structure.

The American Geophysical Union (AGU) is committed to inspiring and educating present and future generations of diverse, innovative, and creative Earth and space scientists. To meet our commitment, AGU provides career and educational resources, webinars, mentoring, and support for students and professionals at each level of development to reduce barriers to achievement and to promote professional advancement. AGU is also working with other organizations and educational institutions to collaborate on projects benefiting the greater geoscience community. The presentation will include an overview of current Pathfinder efforts, collaborative efforts, and an appeal for additional partnerships.

Post-wildfire mudflows have intensified in recent years due to extreme wildfire occurrence, causing significant damage and infrastructure threats. However, despite recent advancements, across-scale geotechnical characterization of mudflow onset and flow behavior remains a challenge. We present a novel experimental and theoretical understanding of the sand type and rain intensity roles on mudflow onset and composition, integrating micromechanics and laboratory experiments. The analysis shows that hydrophobic fine sand, a consequence of wildfires, significantly enhances raindrops’ downhill velocity and splash due to Cassie-Baxter-type surface, as opposed to medium or coarse sand, which affects raindrops as Wenzel surface wettability model. We use micromechanical and single-drop interactions with sand particles to explain erosion on the intermediate scale laboratory tests. Raining experiments on hydrophobic sloped flumes evaluate different slope failure mechanisms in fine, medium, and coarse hydrophobic sand as erosion patterns and seepage induced infinite slope failure in the case of embedded hydrophobic layers. The sand type also affects the spatio-temporal dynamic of erosion onset and distribution of eroded material and overflown rainwater. Surprisingly, we detected a possible equilibrium state where the eroded surface roughness changes affect water overflow and lead to an equilibrium state with very little subsequent erosion under constant rain intensity. On the other hand, erosion gradually increases after the rain starts, reaches a peak, and then subsides very quickly in coarse sand. In contrast, fine sand erosion continues for a longer time but decreases as the surface roughness increases. Furthermore, micromechanical investigation of mixtures of hydrophobic sands, water, and air gives an insight into air entrapment during flow and transport of mudflows. Hydrophobic sand particles attach to air bubbles and form agglomerates, contributing to the mixture heterogeneity and affecting flow and transport properties. Sand particle size, due to gravity, also plays a role in the amount and size of resulting agglomerates. Covering air bubbles with attached sand particles decreases the post-wildfire mudflow density up to 33% in laboratory conditions.

Tropical cyclones dominate the disturbance regime experienced by forest ecosystems in many parts of the world. Interactions between cyclone disturbance regimes and nutrient availability strongly influence forest ecosystem dynamics. However, uncertainty exists over the importance of soil fertility properties (i.e., total soil phosphorus-P concentration) in mediating forest resistance and recovery from cyclone disturbance. We hypothesized that forests on soils with low total P (e.g., developed on limited-P parent material) have a higher resistance to but a slower recovery from cyclone disturbance than forests on high P soils. We investigated cyclone impacts on litterfall, an essential conduit for nutrient recycling in forest ecosystems. We compiled site-level forest litterfall data from 53 studies and datasets associated with 15 naturally-occurring one simulated tropical cyclone in 23 sites within five regions (Taiwan, Australia, Mexico, Hawaii, and the Caribbean)and four cyclone basins. We calculated the effect sizes of cyclone disturbance on the litterfall mass and nutrient (P and nitrogen-N) concentrations and fluxes during the first (< five) years post-disturbance across a total soil P gradient. We also assessed the effect of 20 covariates on the degree of cyclone impact on litterfall. Total litterfall mass flux increased by 4820%following cyclone disturbance. Such an initial increase in litterfall mass reflects the magnitude of cyclone-derived plant material input to the forest floor, which was highest in the Caribbean and lowest in Taiwan. Among 20 covariates, soil P and region were the best predictors of cyclone effects on total litterfall mass, explaining 80% of the variance. The effect sizes increased linearly with soil P and region, from significantly lower in Taiwan (low-P) to largest in the Caribbean (high-P). Total litterfall P and N fluxes increased significantly post-cyclone, whereas the increase in leaf P flux was twice as that in Nflux. Results highlight the importance of understanding the interactions between disturbance and nutrient gradients in forest ecosystems to understand forest responses to altered cyclone regimes expected under climate change.

Background/Question/Methods This project attempts to quantify the resilience of prairie ecosystems to climate change in the Pacific Northwest (PNW). In this region, prairie ecosystems currently sustain ~1.3 million beef cows and calf production costs are expected to increase to offset drought-induced plant productivity loss. Here, we investigate patterns of asymbiotic nitrogen fixation (ANF) and biogeochemical controls, that also influence plant community composition and prairie productivity, under experimental drought to address a major challenge for sustainable agriculture in the region. We hypothesize that the effect of drought on prairie vegetation cover increases soil asymbiotic N inputs by diminishing the dominance of symbiotic root-fungal networks. To test this hypothesis, we quantified the impacts of decadal drought stress on soil ANF using 15N-labeled dinitrogen (15N2) incubations of soils from high- and low-diversity prairies across a 520-km latitudinal gradient (i.e., southern Oregon-SOR, central Oregon-COR, and central Washington-CWA) representing increasingly severe Mediterranean conditions. We also quantified total soil organic carbon-C, total, and available N, and available phosphorus-P and iron-Fe pools to better understand underlying mechanisms governing drought-induced changes in ANF. At each site, composite soil samples (n = 3) were collected from five co-located high- and low-diversity prairie plots under control (ambient) and drought (-40% precipitation) conditions. Results/Conclusions We found that soil ANF response to drought increased with the PNW Mediterranean drought intensity gradient; while ANF rates increased nearly two-fold in the southernmost site (SOR), a significant decrease in ANF was verified in the northernmost site (CWA). ANF response to drought also varied depending on plant diversity, where low-diversity prairies had a more predictable response to drought than high-diversity prairies. For instance, ANF in SOR high-diversity prairies was suppressed but no change was verified in COR high diversity prairies. Soil C and N contents were generally higher in high-diversity prairies whereas treatment had no significant effect across sites. Soil P availability, also affected by drought, and pH were the most important variables explaining ANF variability across vegetation types and sites. Based on our findings, low-diversity prairies in central WA may be those most severely impacted by increased climate change-induced drought stress. Our study highlights the importance of using soil-plant-atmosphere interactions to assess prairie ecosystem resilience to drought in the PNW.

Klinkenberg-corrected gas permeability (k) estimation in tight-gas sandstones is essential for gas exploration and production in low-permeability porous rocks. Most models for estimating k are a function of porosity (ϕ), tortuosity (τ), pore shape factor (s) and a characteristic length scale (lc). Estimation of the latter, however, has been the subject of debate in the literature. Here we invoke two different upscaling approaches from statistical physics: (1) the EMA and (2) critical path analysis (CPA) to estimate lc from pore throat-size distribution derived from mercury intrusion capillary pressure (MICP) curve. τ is approximated from: (1) concepts of percolation theory and (2) formation resistivity factor measurements (F = τ/ϕ). We then estimate k of eighteen tight-gas sandstones from lc, τ, and ϕ by assuming two different pore shapes: cylindrical and slit-shaped. Comparison with Klinkenberg-corrected k measurements showed that τ was estimated more accurately from F measurements than from percolation theory. Generally speaking, our results implied that the EMA estimated k within a factor of two of the measurements and more precisely than CPA. We further found that the assumption of cylindrical pores yielded more accurate k estimates when τ was estimated from concepts of percolation theory than the assumption of slit-shaped pores. However, the EMA with slit-shaped pores estimated k more precisely than that with cylindrical pores when τ was estimated from F measurements.

Tikhonov’s regularization method is the standard technique applied to obtain models of the subsurface conductivity dis- tribution from electric or electromagnetic measurements by solving UT (m) = ||F(m) - d||^2 + P(m): The second term correspond to the stabilizing functional, with P(m) = ||m||^2 the usual approach, and the regularization parameter. Due to the roughness penalizer inclusion, the model developed by Tikhonov’s algorithm tends to smear discontinuities, a feature that may be undesirable. An important requirement for the regularizer is to allow the recovery of edges, and smooth the homogeneous parts. As is well known, Total Variation (TV) is now the standard approach to meet this requirement. Recently, Wang et.al. proved convergence for alternating direction method of multipliers in nonconvex, nonsmooth optimization. In this work we present a study of several algorithms for model recovering of Geosounding data based on Inmal Convolution, and also on hybrid, TV and second order TV and nonsmooth, nonconvex regularizers, observing their performance on synthetic and real data. The algorithms are based on Bregman iteration and Split Bregman method, and the geosounding method is the low-induction numbers magnetic dipoles. Non-smooth regularizers are considered using the Legendre-Fenchel transform.

The coupled operation of fracture, diffusion, and intracrystalline-plastic micromechanisms during semibrittle deformation of rock is directly relevant to understanding crustal processes such as earthquake rupture at the base of the seismogenic zone and failure of salt caverns for energy storage. Triaxial stress-cycling experiments are used to investigate elastic-plastic and viscoelastic behaviors in two synthetic salt-rocks deformed at room temperature and low confinement. During semibrittle flow at high differential stress, porous, granular, work-hardened samples deform predominantly by grain boundary sliding and opening accompanied by minor intragranular cracking and dislocation glide. In contrast, fully annealed, near-zero porosity samples deform at lower differential stress by dislocation glide, grain-boundary sliding and opening accompanied by minor intragranular cracking. During high-stress cycling and semibrittle flow, grain boundary sliding is predominantly frictional; but, associated dispersal of water previously trapped in fluid inclusions can activate fluid-assisted diffusional sliding along grain boundaries at low strain rates. Young’s modulus and Poisson’s ratio are largely controlled by the behavior of closed grain boundaries. Grain boundary sliding accommodated by fluid-assisted diffusion leads to nearly complete stress relaxation after semibrittle flow, and in subsequent low-stress cycling both viscoelasticity and pronounced hysteresis are observed. However, such time-dependent effects vanish with grain boundary healing over days-long holds at low differential stress. Experimental results suggest that within the semibrittle regime, high-stress events can lead to significant transient reduction in viscosity and related phenomena.

The Early Cretaceous Jehol Biota evolution has remarkable spatiotemporal correlation with the destruction of the North China craton though the coupling mechanism remains enigmatic. The craton destruction was accompanied by intense magmatic activity and the released volatiles and nutrients might have had climatic and environmental impacts on the biotic evolution. In this study, we investigated the mentioned hypothetical causal link by determining concentrations and total emissions of volatile elements (S, F, Cl) and bulk-rock P contents of volcanic rocks that were erupted during the pre-flourishing, flourishing and post-flourishing stages of the Jehol Biota. Our results show that the volcanism near the flourishing stage has lower S (1083-2370 ppm), Cl (1277-5608 ppm) and higher P2O5 contents (0.48-0.84 wt.%) than that in non-flourishing stages with S of 1991-3288 ppm, Cl of 7915-12315 ppm and P2O5 of 0.17-0.23 wt.%. Fluorine contents in the three stages vary from 893 to 3746 ppm. The total volatile emissions are minor in the flourishing stage (3.6-6.6 Gt S, 2.2-4.6 Gt Cl and 2.1-4.0 Gt F) but elevated in the non-flourishing stages (1-690 Gt S, 4-934 Gt Cl and 1-308 Gt F). Our data suggest that regional climatic and environmental impacts of volcanism in the non-flourishing stages probably hindered the species diversification. The high P flux released from lithospheric mantle-derived lavas during the peak time of craton destruction might enhance primary productivity and contribute to the flourishing of the Jehol Biota. Our study provides insights into the relationship between the biosphere and deep geodynamic processes driven by volcanism.

Despite the importance of turbidity currents in environmental and resource geology, their flow conditions and mechanism are not well understood. To resolve this issue, a novel method for the inverse analysis of turbidity current using deep learning neural network (DNN) was proposed. This study aims to verify this method using artificial and flume experiment datasets. Development of inverse model by DNN involves two steps. First, artificial datasets of turbidites are produced using a forward model based on shallow water equation. To develop a inverse model, DNN then explores the functional relationship between initial flow conditions and characteristics of the turbidite deposit through the processing of artificial datasets. The developed inverse model was applied to 200 sets of artificial test data and four sets of experiment data. Results of inverse analysis of artificial test data indicated that the flow conditions can be precisely reconstructed from depositional characteristics of turbidites. For experimental turbidites, spatial distributions of grain size and thickness were accurately reconstructed. With regard to hydraulic conditions, reconstructed values of flow heights, sediment concentrations, and flow durations were close to the measured values. In contrast to the other values, there was a larger discrepancy between the measured and reconstructed values of flow velocity, which may be attributed to inaccuracies in sediment entrainment functions employed in the forward model.

The Braiding Index (BI), defined as the average count of intercepted channels per cross-section, is a widely used metric for characterizing multi-thread river systems. However, it does not account for the diversity of channels (e.g., in terms of discharge) within different cross-sections, omitting important information related to system complexity. Here we present a modification of BI (the Entropic Braiding Index, eBI) which augments the information content in BI by using Shannon Entropy to encode the diversity of channels in each cross section. eBI is interpreted as the number of “effective channels” per cross-section, allowing a direct comparison with the traditional BI. We demonstrate the superior capabilities of eBI via analysis of synthetic, numerical and field examples. In addition, we show that interrogating cross-sections via the ratio BI/eBI has the potential to quantify channel disparity, differentiate types of multi-thread systems, and inform about cross-section stability to forcing variability (e.g., seasonal flooding).

The shallow 1971 Mw 6.6 San Fernando, California earthquake involved a complex rupture process on an immature thrust fault with a non-planar geometry, and is notable for having a higher component of left-lateral surface slip than expected from seismic models. We extract its 3-D coseismic surface displacement field from aerial stereo photographs and document the amount and width of the vertical and strike-parallel components of distributed deformation along strike. The results confirm the significant left-lateral surface offsets, suggesting a slip vector rotation at shallow depths. Comparing our offsets against field measurements of fault slip, we observe that most of the offset was accommodated in the damage zone, with off-fault deformation averaging 68% in both the strike-parallel and vertical components. However, the magnitude and width of off-fault deformation behave differently between the vertical and strike-parallel components, which, along with the rotation in rake near the surface, can be explained by dynamic rupture effects.

Modern Ocean is characterized by the formation of deep-water in the North Atlantic (i.e. NADW). This feature has been attributed to the modern geography, in which the Atlantic Ocean is a large basin extending from northern polar latitudes to the Austral Ocean, the latter enabling the connection of the otherwise isolated Atlantic with the Pacific and Indian Oceans. Sedimentary data date the establishment of the NADW between the beginning of the Eocene (∼49 Ma) and the beginning of the Miocene (∼23 Ma). The objective of this study is to quantify the impact of Miocene geography on NADW through new simulations performed with the earth system model IPSL-CM5A2. We specifically focus on the closure of the eastern Tethys seaway (dated between 22 and 14 Ma), which allowed the connection between the Atlantic and Indian Oceans, and on the Greenland ice sheet, whose earliest onset remains open to discussion but for which evidence suggest a possible existence as early as the Eocene. Our results show that the closure of the eastern Tethys seaway does not appear to impact the establishment of NADW, because waters from the Indian Ocean do not reach the NADW formation zone when the seaway is open. Conversely, the existence of an ice sheet over Greenland strengthens the formation of NADW owing to topography induced changes in wind patterns over the North Atlantic, which in turn, results in a larger exchange of water fluxes between the Arctic and the North Atlantic, and in a re-localization of deep-water formation areas.

Topographic features are commonly interpreted to represent interactions between tectonic and climate-driven processes. However, recent work has highlighted how drainage reorganization from river capture may produce landscapes that resemble those generated by changing tectonic conditions and emphasized the importance of developing tools and metrics to identify the source of landscape transience (Yang et al., 2015; Whipple et al., 2017). While few studies have sought to estimate the rates and magnitudes of increased transient incision resulting from river capture (e.g. Prince et al., 2011, Yanites et al., 2013), the ability to quantify river capture-related incision is vital to improve our characterization of landscape responses to transience. This work tests the hypothesis that the observed incision and distribution of knickpoints in the Sutlej river network of the western Himalaya is the result of an ongoing transient response to a large-scale river capture event that occurred in the late Pleistocene. A combination of topographic analyses using digital elevation models, knickpoint propagation modeling, 1-D numerical incision modeling, and landscape evolution modeling are used in conjunction with new and existing field-derived data (e.g. cosmogenic radionuclide-derived erosion rates and (U-Th)/He and fission track thermochronology) to quantify the magnitude and timing of the transient landscape response. Redistribution of drainage area and the subsequent enhancement of incision along the Sutlej may explain the increased amounts of Himalayan detritus delivered to the Indus fan since 5 Ma (Clift and Blusztajn, 2005). Similar large-scale river capture events proposed throughout the Himalaya (e.g. Garzione et al., 2003; Van Der Beek et al., 2018), suggest that capture events may be a regional phenomenon inherent to the Himalayan orogen and imply that river capture may be an important contributor to the distribution of sediment along collisional margins.

Densely spaced GPR and complex resistivity measurements on a 30,000 square meters site in a region of enigmatic sinkhole occurrences in unconsolidated Quaternary sediments have featured unexpected and highlighting results from both a meteorite impact research and an engineering geology point of view. The GPR measurements and a complex resistivity/IP electrical imaging revealed extended subrosion depressions related with a uniformly but in various degrees of intensity deformed loamy and gravelly ground down to at least 10 m depth. Two principle observations could be made from both the GPR high-resolution measurements and the more integrating resistivity and IP soundings with both petrophysical evidences in good complement. Subrosion can be shown to be the result of prominent sandy-gravelly intrusions and extrusions typical of rock liquefaction processes well known to occur during strong earthquakes. Funnel-shaped structures with diameters up to 25 m near the surface and reaching down to the floating ground water level at 10 m depth were measured. GPR radargrams could trace prominent gravelly-material transport bottom-up within the funnels. Seen in both GPR tomography and resistivity/IP sections more or less the whole investigated area is overprinted by wavy deformations of the unconsolidated sediments with wavelengths of the order of 5 - 10 m and amplitudes up to half a meter, likewise down to 10 m depth. Substantial earthquakes are not known in this region. Hence, the observed heavy underground disorder is considered the result of the prominent earthquake shattering that must have occurred during the Holocene (Bronze Age/Celtic era) Chiemgau meteorite impact event that produced a 60 km x 30 km sized crater strewn field directly hosting the investigated site. Depending on depth and size of floating aquifers local concentrations of rock liquefaction and seismic surface waves (probably LOVE waves) to produce the wavy deformations could develop, when the big disintegrated meteoroid (a loosely bound asteroid or a comet of roughly estimated 1 km size) hit the ground. The observations in the Chiemgau area emphasize that studied paleoliquefaction features and wavy deformations (e.g. seismites) need not necessarily have originated solely from paleoseismicity but can provide a recognizable regional impact signature.

Pore water freshening (i.e., decreases in dissolved Cl) has been documented in marine sediments along most active margins, with the migration of deep fluids or methane hydrate dissociation often invoked as sources of freshening in the sediment column. During D/V JOIDES Resolution Expedition 379T in 2019, two new sites (J1005 and J1006) were cored near ODP Site 1233 (41°S), adjacent to a seafloor mound venting structure. The three sites are less than 10 km apart but show marked differences in pore water chemistry and methane hydrate occurrence. The extent of Cl decrease is a function of distance from the mound, with the strongest freshening occurring at the closest site (J1006), which is the only site where methane hydrate was observed. Methane fluxes follow the same pattern, suggesting a common control. Increasing oxygen and decreasing hydrogen isotopes point to deep mineral bound water as the primary source of freshening near the mound, with fluids originating ~2.5 km below seafloor near the décollement. Secondary influences from methane hydrate dissociation and ash diagenesis also appear to influence regional pore water chemistry. The variability in pore water freshening suggests that fluid migration and eventual expulsion at the venting structure follows narrow pathways, likely along faults within the forearc complex. The migration of deep, gas-charged fluids may also support methane hydrate saturations greater than in situ organic carbon diagenesis would allow, but nonetheless consistent with geophysical estimates. Together, the data highlight an important link between fluid migration and methane hydrate formation on the Chilean Margin.

Lava tubes can offer protection for human crews and their equipment on other solar system bodies, in particular from radiation threats and extreme surface temperatures. Developing strategies to survey regions of other terrestrial bodies (such as the Moon or Mars) for tubes suitable for potential habitation will likely become an important part in planning future space exploration projects. A variety of surface geophysical techniques, such as ground penetrating radar (GPR) have the potential to help recognize and map tubes. GPR shows promise for providing high resolution information on tube geometries. To investigate GPR’s capacity and limitations, we use GPR, as well as comparative methods of seismic and magnetic surveys, in conjunction with LiDAR mapping of tube interiors at the Lava Beds National Monument (LBNM) in California, USA. LBNM offers a wide variety of tube geometries and textures. We have collected 2D GPR profiles and small 3D GPR grids (of parallel 2D lines) with antenna frequencies of 100 and 200 MHz on four lava tubes with different geometries, textures and at different depths. Challenges in recovering tube geometries include wave scattering in fractured rock covering tubes, irregular and “drippy” ceilings and walls, and blocky floors. Our primary results show that the top of the LBNM tubes can generally be resolved in the GPR data, while resolving the bottom is more challenging. The utility of various GPR processing techniques can be directly assessed by comparing resolved GPR images against the LiDAR-measured tube geometries.

If a kick is not detected and circulated properly out of the wellbore with heavier mud weight, it leads to blowouts. In this case, reservoir fluids gush out of the well uncontrollably without restriction leading to loss of control. This may lead to fractures initiating in the post-blowout capping stages, just below the casing shoe, propagating upwards creating a channel through which reservoir fluids can flow to the ocean floor. Being able to model these fracture failures will help understand wellbore integrity problems from loss of control situations and predict the possibility of broaching preventing many ecological disasters like the 1969 Santa Barbara oil spill from Union Oil’s A-21 well. The hypothesis tested is that fracture initiation from a wellbore in a loss of control situation can be predicted through analysis of the near-wellbore stress field, with knowledge of the in-situ stress state and the properties of the formation and the borehole assembly. A 3D numerical model is employed to assess whether a fracture will initiate. This is done by considering the stressfield at the casing shoe; the point most vulnerable to tensile fracture failure downhole. In-situ stress state, wellbore pressure, casing shoe depth and the casing, cement, and formation’s mechanical properties are independent variables that are shown to control fracture initiation; the dependent variable. A reservoir model is used to predict pressure build-up during capping procedures. A case study on Gulf of Mexico is presented with input wellbore pressure data generated using a worst case discharge model. Wellbore pressure drop during uncontrolled discharge from a well can cause casing collapse failures and subsequently pressure build-up in the post-blowout capping stage, may initiate fractures which can lead fluid leakage to the surface either through the cement or the interfaces with the casing and the formation. The region of the in-situ stress states where fracture initiation will occur is shown in dimensionless plots. This is useful for drilling and wellbore integrity teams. When targeting highly-pressured formations as in deepwater, wellbore architecture must be made with considerations of the wellbore pressures generated from loss of control situations like blowouts. Research reported in this publication was supported by an Early-Career Research Fellowship from the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine.