NASA’s InSight mission records several high-frequency (>0.5 Hz) dispersive seismic signals. These signals are due to the acoustic-to-seismic coupling, where the infrasound is generated by meteorite entry and impacts. This dispersion property is due to infrasound propagating in a structured atmosphere, and we refer to this infrasound as guided infrasound. We propose to model the propagation of guided infrasound and the seismic coupling to the ground analytically; we use a 1D layered atmosphere on a three-layer solid subsurface medium. The synthetic ground movements fit the observed dispersive seismic signals well. We also examine and validate the previously-published subsurface models derived from the InSight ambient seismic vibration data.

The increasing amount of Synthetic Aperture Radar (SAR) satellites orbiting the Earth, their increasing time and space resolution, the variety of wavelengths, polarizations and looking geometries, the shortening of data availability latency and the lengthening of archive databases offer unprecedented opportunities for Earth observation and hazard monitoring. The downside is that it brings new challenges for processing that huge amount of data and for making the results quickly analyzable. To fully benefit from these advances in SAR, it requires efficient data processing infrastructure (optimized for processing speed, storage usage and security), efficient data visualization, and standardization of the final products for easy ingestion by conventional analysis tools. We present here the InSAR Mass processing Toolbox for Multidimensional time series (MasTer), which can combine any type of SAR data to produce unsupervised vertical and horizontal ground deformation time series. MasTer is optimized to automatically download SAR data, select the appropriate interferometric pairs, perform the interferometric mass processing, compute the geocoded deformation maps, invert and display the velocity maps and the 2D time series on a web page updated incrementally as soon as a new image is made available. The incremental architecture allows updating the time series within the shortest time possible (typically a few hours) as soon as a new SAR image is provided. Several steps are self-evaluating to ensure robust and reliable processing. Moreover, recent methodological improvement consists in the computation of a coherence proxy to guide the pair selection optimization balancing the use of each image as primary and secondary image during the differential interferometric (DInSAR) processing. Such a pair selection increases both the processing efficiency and the signal-to-noise ratio of the time series. MasTer also allows the production of time series of coherences or SAR amplitude images, which can be used e.g. for land use monitoring or geomorphological changes detection. The capabilities and performances of MasTer will be illustrated with several examples. Software and manual are available upon request from the authors.

A comprehensive surface displacement monitoring system installed in the recently deglaciated bedrock slopes of the Aletsch Valley shows systematic reversible motions at the annual scale. We explore potential drivers for this deformation signal and demonstrate that the main driver is pore pressure changes of phreatic groundwater in fractured granitic mountain slopes. The spatial pattern of these reversible annual deformations shows similar magnitudes and orientations for adjacent monitoring points, leading to the hypothesis that the annually reversible deformation is caused by slope-scale groundwater elevation changes and rock mass properties. Conversely, we show that the ground reaction to infiltration from snowmelt and summer rainstorms can be highly heterogeneous at local scale, and that brittle-ductile fault zones are key features for the groundwater pressure-related rock mass deformations. We also observe irreversible long-term trends (over the 6.5 yr dataset) of deformation in the Aletsch valley composed of a larger uplift than observed at our reference GNSS station in the Rhone valley, and horizontal displacements of the slopes towards the valley. These observations can be attributed respectively to the elastic bedrock rebound in response to current glacier mass downwasting of the Great Aletsch Glacier and gravitational slope deformations enabled by cyclic groundwater pressure-related rock mass fatigue in the fractured rock slopes.

We report here a preliminary investigation on site effects in a highly populated zone of academic importance. The study area is mostly characterized by its alluvial sediments. Due to its rapid development with construction of high-rise buildings and presence of active Kopili fault nearby, the site effects analysis in this area has become very crucial which is further fueled by a strongly felt earthquake of 6.4 M occurring recently; whose epicenter was just 40 Km away from this study area. Accordingly, an attempt is made to assess site related parameters by accruing ambient vibration records at 16 single stations covering. Via horizontal to vertical spectral ratio (HVSR) analysis, we estimate the resonant frequencies. Likewise, we compute the HVSR amplification values. Apart from this, liquefaction vulnerability indices were estimated for the study region. With a fair corroboration with borehole data, the findings reveal a low velocity zone. The heterogenous distribution of resonant frequencies and assorted amplification implicate a varying overburden thickness; thereby augmenting the Kg values at certain places. In the context of the recent 6.4 M earthquake, the results are poised to play a pivotal role so far hazard mitigation is concerned.

Boulder-sized clasts are common on the surface of Mars, and many are sufficiently large to be resolved by the High Resolution Imaging Science Experiment (HiRISE) camera aboard the Mars Reconnaissance Orbiter (MRO). The size, number, and location of boulders on the surface and their spatial distribution can reveal the processes that have operated on the surface, including boulder erosion, burial, impact excavation, and other mechanisms of boulder transport and generation. However, quantitative analysis of statistically significant boulder populations which could inform these processes entails prohibitively laborious manual segmentation, granulometry and morphometry measurements over large areas. Here we develop and describe an automated tool to locate and measure boulders on the martian surface: the Martian Boulder Automatic Recognition System (MBARS). The open-source Python-based toolkit autonomously measures boulder diameter and height in HiRISE images enabling rapid and accurate assessments of boulder populations. We compare our algorithm with existing boulder-counting methodologies, manual analyses, and objects of known size to verify accuracy and precision. Additionally, we test MBARS quantitatively characterizing boulders around an impact crater in the martian northern lowlands. We compare this to previous work on rock excavation during impact cratering using manually counted boulders around lunar craters.

Completely carbonated peridotites represent a window to study reactions of carbon-rich fluids with mantle rocks. Here we present details on the carbonation history of listvenites close to the basal thrust in the Samail ophiolite. We use samples from Oman Drilling Project Hole BT1B, which provides a continuous record of lithologic transitions, as well as outcrop samples from listvenites, metasediments and metamafics below the basal thrust of the ophiolite. 87Sr/86Sr of listvenites and serpentinites, ranging from 0.7090 to 0.7145, are significantly more radiogenic than mantle values, Cretaceous seawater, and other peridotite hosted carbonates in Oman. δ13C in the listvenites and serpentinites range from -10.6‰ to 1.92‰, including a small organic carbon component with δ13C as low as -27‰ that reaffirms the presence of carbonaceous material in Hole BT1B. The source of the radiogenic Sr was probably similar to Hawasina metasediments that underlie the ophiolite, with values up to 0.7241 in clastic lithologies. These results indicate that decarbonation reactions in such clastic sediments, during subduction at temperatures above 500°C, form carbon rich fluids that could have migrated updip, supplying radiogenic 87Sr/86Sr and fractionated δ13C to BT1B serpentinites and listvenites.

Explosive, ash-producing volcanic eruptions are a significant natural hazard with the potential for loss of life, economy, and infrastructure. Turrialba is an active stratovolcano located in the Central Cordillera of Costa Rica. The edifice is located only 35 km east-northeast of Costa Rica's capital city and poses a threat to its central valley, the social and economic hub where more than half of the population resides. The most recent eruption took place in 2016-2017, consisting of four eruption phases. Preliminary observations using SEM show significant morphological differences between the various eruption phases, including the amount of dust and crystals that are present. The morphology of volcanic ash is fundamental to our understanding of magma fragmentation, and in transport modeling of volcanic plumes and clouds. The chemistry of the ash particles produced by fragmenting magmatic foams may affect their evolving morphology throughout the various stages of eruption. In addition, eruption energetics may play a role in ash morphology. Separating the roles of chemical heterogeneity and evolving energetics requires careful examination of ash morphology and its relation to composition. In this way, we take some initial steps in closing the knowledge gap between eruption mechanisms and how and why these mechanisms are exhibited in the morphology of ash during explosive eruptions.

Deep carbon is terrestrial carbon that is not in the atmosphere or oceans or on the surface. We have a great deal of knowledge about the properties of near surface carbon, but relatively little is known about the deep carbon cycle. The Deep Carbon Observatory, was founded in 2009, to address major questions about deep carbon. Where are the reservoirs of carbon? Is there significant carbon flux between the deep interior and the surface? What is deep microbial life? Did deep organic chemistry have a role in the origin of life? This project is directed toward documenting and describing of the history of deep carbon science. The narrative begins in 1601, when William Gilbert suggested that Earth's interior behaves like a giant bar magnet. We trace across three centuries the slow evolution of thought that led to the establishment of the interdisciplinary field of Earth System Science. The concept and then development of the deep carbon cycle of burial and exhumation dates back at least two hundred years. We identify and document the key discoveries of deep carbon science, and assess the impact of this new knowledge on geochemistry, geodynamics, and geobiology. A History of Deep Carbon Science is in preparation for publication by Cambridge University Press in 2019. Its illuminating narrative highlights the engaging human stories of many remarkable researchers who have discovered the complexity and dynamics of Earth's interior.

In this study, we detail a new prediction-oriented procedure aimed at volcanic hazard assessment based on geophysical mass flow models with heterogeneous and poorly constrained output information. Our method is based on an itemized application of the empirical falsification principle over an arbitrarily wide envelope of possible input conditions. In particular, instead of fully calibrating input data on past observations, we create and explore input values under more general requirements of consistency, and then we separately use each piece of empirical data to remove those input values that are not compatible with it, hence defining partial solutions to the inversion problem. This has several advantages compared to a traditionally posed inverse problem: (i) the potentially non-empty intersection of the input spaces of partial solutions fully contains solutions to the inverse problem; (ii) the partial solutions can provide hazard estimates under weaker constraints potentially including extreme cases that are important for hazard analysis; (iii) if multiple models are applicable, specific performance scores against each piece of empirical information can be calculated. We apply our procedure to the case study of the Atenquique volcaniclastic debris flow, which occurred in the State of Jalisco (MX), 1955. We adopt and compare three depth averaged models currently implemented in the TITAN2D solver, available from vhub.org. The associated inverse problem is not well-posed if approached in a traditional way. However, we show that our procedure can extract valuable information for hazard assessment, allowing the exploration of the impact of model flows that are similar to those which occurred in the past, but differ in plausible ways.

In this study, we use a doubly stochastic model to develop a short-term eruption forecasting method based on precursory signals. The method enhances the Failure Forecast Method (FFM) equation, which represents the potential cascading of signals leading to failure. The reliability of such forecasts is affected by uncertainty in data and volcanic system behavior and, sometimes, a classical approach poorly predicts the time of failure. To address this, we introduce stochastic noise into the original ordinary differential equation, converting it into a stochastic differential equation, and systematically characterize the uncertainty. Embedding noise in the model can enable us to have greater forecasting skill by focusing on averages and moments. In our model, the prediction is thus perturbed inside a range that can be tuned, producing probabilistic forecasts. Furthermore, our doubly stochastic formulation is particularly powerful in that it provides a complete posterior probability distribution, allowing users to determine a worst-case scenario with a specified level of confidence. We verify the new method on simple historical datasets of precursory signals already studied with the classical FFM. The results show the increased forecasting skill of our doubly stochastic formulation. We then present a preliminary application of the method to more recent and complex monitoring signals.

Multiple generations of ductile and brittle deformation recorded in the Obsidian Dome lava, California, inform on the rheological complexities of silicic lava emplacement. Understanding the non-linear rheological evolution of advancing lava is key to improving understanding of the durations, extents, and explosive hazards of future eruptions. Numerous studies of silicic lavas, at Obsidian Dome in particular, have focused on micro-scale textures and features interpreted to record flow within the conduit, primarily. How the lava flowed as a growing mass outside the conduit is largely unconstrained. Field observations at Obsidian Dome identify cycles of ductile flow followed by brittle fracturing, followed by relaxation and continued flow. Mode 1 vertical fractures often served as conduits for tephra venting, presumably following spontaneous exsolution-driven vesiculation and volume expansion deeper in the lava. Tephra, often tack-welded to the fracture surfaces, are preserved in many fractures that clearly closed-up on relaxation of the obsidian. Therefore, crossing the glass transition was likely strain rate driven, rather than cooling- or exsolution-driven that would have inhibited relaxation after the stress was released. The interplay between flow and fracturing is also evident in the ubiquity of crease structures at decimeter to decameter scales over all of Obsidian Dome. Unraveling the complexities of flow and fracturing in obsidian lavas will require and enable improved understanding of similarly non-linear rheological evolutions in ice, salt, the mid crust, and the asthenosphere.

Improving constraints on the basal ice/bed properties is essential for accurate prediction of ice-sheet grounding-line positions and stability. Furthermore, the history of grounding-line positions since the Last Glacial Maximum has proven challenging to understand due to uncertainties in bed conditions. Here we use a 3D full-Stokes ice-sheet model to investigate the effect of differing ocean bed properties on ice-sheet advance and retreat over a glacial cycle. We do this for the Ekström Ice Shelf catchment, East Antarctica. We find that predicted ice volumes differ by >50%, resulting in two entirely different catchment geometries triggered exclusively by variable ocean bed properties. Grounding-line positions between simulations differ by >100% (49 km), show significant hysteresis, and migrate non-steadily with long quiescent phases disrupted by leaps of rapid migration. These results highlight that constraints for both bathymetry and substrate geologic properties are urgently needed for predicting ice-sheet evolution and sea-level change.

The flow and stability of liquid through a tube at subfreezing temperature can be modified by the upstream flow conditions. A simplified model for the dynamics is used to show behavior 3 different upstream configurations. When certain stability parameters are met: 1. A compressible reservoir has oscillatory behavior . 2. A tube fed by a constriction with a large upstream pressure behaves like a freezing faucet during winter. 3. Multiple tubes connected by an upstream manifold evolve to some selected flowing tubes and others seeping with their spacing inversely proportional to manifold flow resistance. Numerically, a minimum radius needs to be invoked in many cases to avoid excessive upstream pressure. Results have numerous applications such as wintertime ice formation at natural springs, the formation of magma tubes, spacing of volcanism, and the distance that liquid flows through freezing surroundings

Axial Seamount is the most active submarine volcano in the NE Pacific Ocean, and is monitored by instruments connected to a cabled observatory (the US Ocean Observatories Initiative Cabled Array), supplemented by autonomous battery-powered instruments on the seafloor (at ~1500 m depth). Axial is a basaltic hot spot volcano superimposed on the Juan de Fuca spreading ridge, giving it a robust and apparently continuous magma supply. It has had three effusive eruptions in the last 21 years: in 1998, 2011, and 2015. Deformation measurements have been conducted at Axial Seamount since the late 1980’s with bottom pressure recorders (BPRs) that can detect vertical movements of the seafloor with a resolution of ~1 cm. This monitoring has produced a 22+ year time-series including co-eruption rapid deflation events of 2.5-3.2 meters, separated by continuous gradual inter-eruption inflation at variable rates between 15-80 cm/yr. The overall pattern appears to be inflation-predictable, with eruptions triggered at or near a critical level of inflation. Using this pattern, the 2015 eruption was successfully forecast within a one-year time window, 7 months in advance. As of December 2019, Axial Seamount has re-inflated 1.98 m (~78%) of the 2.54 m it deflated during the 2015 eruption. We are exploring several methods to forecast the next eruption, including daily extrapolation of the average rate of inflation from OOI BPR data during the last 3 months forward in time until it intersects the threshold reached before the 2015 eruption. Using this method with the difference in inflation between two OOI BPR instruments located 3.5 km apart removes noise from tidal residuals and oceanographic signals that are common to both instruments. This method suggests the next eruption is likely between 2020 and 2024. However, this simple method is complicated by uncertainties in the next inflation threshold (the volcano inflated 20 cm higher before the 2015 eruption compared to 2011), changes in the rate of inflation with time, and by intermittent pauses in the inflation (and seismicity) observed since 2015 that have lasted from a week to several months.

Nagaland is part of the northern extension of the Indo Myanmar range(IMR).This area is representative of several orogenic upheavals in the Cretaceous-Tertiary that form a relativelyyoung and mobile land belt.Nagaland is the most recent crustal reaction to the collision of theIndian and Burmese Plate.Barail formation emerged at the active margin of the Indo-Burmeseplateconvergence.The majority of the available tectonic replica proposes that themalformation and uplift of the Northeastern. We aimed at the highlights of exhumation andsedimentation, and its other host processes like provenance characteristics of the Barail sandstones from Nagaland, India.Systematic geological mapping of approximately 50 square meters has been carried out in the study area.A geological map of the study area was made on a scale of 1:50,000 in the Indian Topsheet No.58M/4 survey in the Kohima district of Nagaland.The region was mapped according to need and accessibility by taking the traverses along the highways, footpaths and across the ranges.In this study,four quarry samples disseminated in various folds in the Barail Group yielded the ages ranging from 37.4±1.5Ma to 49.9±2.4Ma and younger than their predecessor sedimentary deposition ages(86.92-181.81Ma).The binomial distribution clearly stated that from 46.0to32.0Ma,the grain ages fitted peaks are usually dominated by the youngpeak.Combined with an interpretation of the origin,the detrital zircon of the young peak age and rocks indicated that most significant uplifting of the Barail Group occurred during EocenetotheOligocene,almost timed to coincide with the colliding of the Indo-Burmese plate more around ~35-50Ma.Such findings have been consistent with the current geology of Naga Hills in theprovince of Nagaland.

For over half a century, the bedding plane orientation was believed to be the main cause of the mechanical anisotropy in shales. However, the in situ stress may also play an important role on the mechanical anisotropy. In this paper, shales from the Longmaxi formation were sampled from Fulin, Chongqing, China. The axial orientations of all the cylinder samples (50mm, 100mm height) of Longmaxi Shale are parallel to the bedding plane. The cylinder samples were compressed in a triaxial apparatus of under confining pressures from 0 to 25MPa and at a strain rate of 4*10-2mm*min-1. The only difference of the samples in this study is the in situ stress orientations in the way that the samples in the X group are along the major principle stress while those in the Y group are along the minor principal stress. The Young’s modulus, failure strength, and Poisson’s ratio as a function of confining pressure were determined for both the two groups of samples. The result shows that, for all confining pressures, Young’s moduli in the X group are higher than those of Y group if confining pressures are the same and the differences are 2.89 GPa in average. For confining pressures within 20MPa, the failure strengths and Poisson’s ratios are higher in the X group. The differences of failure strengths and Poisson’s ratios between the two groups for the same confining pressures decrease with the increase of confining pressures. When confining pressures exceed 20MPa, the failure strengths and Poisson’s ratios in the Y group are higher than those in the X group, and the differences of failure strengths and Poisson’s ratios between the two groups for the same confining pressures increase with the increase of confining pressures. Therefore, the differences of mechanical properties of the samples along different directions of in situ stress suggest the Longmaxi gas shale is not transversely isotropic but anisotropic in three dimensions. Considering that all samples have the same bedding plane, the mechanical anisotropy of samples detected in the experiments may be owing to the divergences of the minerals and micro- cracks in the bedding plane. As there were changes of the differences between X group and Y group, the variations might be an indicator of the in situ stress.

This paper reports on the progresses obtained through the analysis of thermomagnetic features of the region between the southern part of Tocantins state and the northern part of Goias state, in Central Brazil. For that, we made use of data collected through aeromagnetic surveys. Techniques of shading applied to vertical derivative of Anomaly Magnetic Field (AMF) have been used to identify magnetic lineaments. The depth estimates of these structures were obtained by means of spectral Analysis of AMF (Centroid method). The results reveal the existence of a set of near-linear magnetic features in the region between the longitudes of 480W and 510W and between the latitudes of 120S and 140S. This is also an area of moderate microseismic activity and recent studies indicate anomalous geothermal conditions at the upper crust. However, direct evidences of the occurrence of magmatic intrusions at shallow crustal levels are absent. We postulate the hypothesis that the features identied as a result of aeromagnetic survey are indicative of fracture systems, thereby enabling the ow of carbonic uids observed at the region’s thermal springs and transporting geothermal heat.

Artisanal and small-scale gold mining (ASGM) represents a significant economic activity for communities in developing countries. In south-eastern Senegal, this activity has increased in recent years and has become the main source of income for the local population. However, it is also associated with negative environmental and social impacts. Considering the recent development of ASGM in Senegal, and the difficulties of the government in monitoring and regulating this activity, this article proposes a method for detecting and mapping ASGM sites in Senegal using Sentinel 2 data and the Google Earth Engine. Two artisanal mining site in Eastern Senegal are selected to develop and test this approach. Detection and mapping are achieved using Principle Component Analysis (PCA), Separability and Threshold (SEaTH) and Support Vector Machine classifier (SVM). The results are validated by ground-truth observations. The PCA indicates that the best period for identifying artisanal mining sites against other types of land-use is the end of dry season, when vegetation is minimal. This result is confirmed by examining the spectral evolution over time of different types of land-use. Input variables for SVM classification are defined by the SEaTH. The classification results are presented as a map with 5 color-coded categories of land-use. The method can be used to map the evolution of mining sites as a function of time using future Sentinel acquisitions. This approach may also be extrapolated to other areas in the Sahel where authorities are also confronted with the difficult regulation of artisanal gold mining activities in remote areas.

Previous studies have shown that Mt. Sharp has stratigraphic variation in mineralogy that may record a global transition from a climate more conducive to clay mineral formation to one marked by increased sulfate production. To better understand how small-scale observations along the traverse path of NASA’s Curiosity rover might be linked to such large-scale processes, it is necessary to understand the extent to which mineral signatures observed from orbit vary laterally and vertically. This study uses newly processed visible-near infrared CRISM data and corresponding visible images to re-examine the mineralogy of lower Mt. Sharp, map mineral distribution, and evaluate stratigraphic relationships. We demonstrate the presence of darker-toned strata that appears to be throughgoing with spectral signatures of monohydrated sulfate. Strata above and below this zone are lighter-toned and contain polyhydrated sulfate and variable distribution of Fe/Mg clay minerals. Clay minerals are observed at multiple stratigraphic positions; unlike the kieserite zone these units cannot be traced laterally across Mt. Sharp. The kieserite zone appears to be stratigraphically confined, but in most locations the orbital data do not provide sufficient detail to determine whether mineral signatures conform to or cut across stratigraphic boundaries, leaving open the question as to whether the clays and sulfates occur as detrital, primary chemical precipitates, and/or diagenetic phases. Future observations along Curiosity’s traverse will help distinguish between these possibilities. Rover observations of clay-bearing strata in northwest Mt. Sharp may be more reflective of local conditions that could be distinct from those associated with other clay-bearing strata.

Data-model comparisons are common when addressing (paleo)climate questions. Many applications require deriving continuous surface fields of scalar variables from a set of irregularly distributed data points, typically for model validation against data or data-derived model input as initial or boundary conditions. While various interpolation techniques and interfaces exist, few can simultaneously: (1) interpolate across local to global spatial scales, (2) perform anisotropic interpolation using the spatial structure derived from the data instead of an assumed one, and (3) explicitly derive uncertainty in the interpolated fields due to both data density and measurement error. We present a standalone interpolation toolbox including a graphical user interface (GUI), which is aimed at the general earth science community. It uses a kriging algorithm whose distance metric is the geodesic on an oblate spheroid, be it the WGS-84 reference ellipsoid for applications on the surface of the Earth, or an equivalent ellipsoid with varying radii for interpolation on vertical levels above the surface. While kriging algorithms exist that perform interpolation on such non-Euclidean distances, they do not provide a check for conditionally negative semi-definiteness (CNSD) of the variogram matrix, which is a requisite for the kriging method. Since mathematical theory of kriging on spheroids or ellipsoids has not yet provided a set of authorized variance-distance functions, we incorporated a numerical check for CNSD condition for each data realization and variance-distance modeling scheme. The GUI will allow the user a high degree of customization. Preliminary results are promising, with robust results for isotropic interpolation. The derivation of CNSD variogram matrices for anisotropic interpolation remains the major challenge of the project. When completed, ClimAG-Krigger will provide the community with an easy-to-use, robust tool for anisotropic global kriging that will be specifically tailored for (paleo)climate applications.

The rhyolite-producing Laguna del Maule volcanic field (LdMVF) records magma-induced surface inflation rates of ~ 25 cm/year since 2007. During the Holocene, ~60 meters of cumulative surface uplift is recorded by paleoshorelines of the Laguna del Maule, located on the southeast edge of the LdMVF (Chile-Argentina border) near the Barrancas volcanic complex. Rhyolites from the Barrancas complex erupted over ~14 ka including some of the youngest (1.4 ± 0.6 ka) lava flows in the field. New gravity data collected on the Barrancas complex reveals a Bouguer low (-6 mGal, Barrancas anomaly) that is distinct from the pronounced gravity low (-19 mGal; Lake anomaly) associated with present-day deformation and magma intrusion to the north. Three-dimensional inversion of the Barrancas anomaly indicates the presence of a magma body with a maximum density contrast of -250 kg/m3 centered at a depth of ~ 3 km below surface. Comparison of model densities with measured densities from nearby silicic plutons suggest that a magma body, containing < 30 % melt phase and a low volatile content, exists beneath the Barrancas complex. The Barrancas and Lake gravity lows represent magma in different physical states, associated with past and present-day storage beneath the LdMVF. The gravity model mirrors existing geochemical observations which independently indicate that at least two distinct rhyolites were generated and stored as discrete magma bodies within the broader LdMVF. Small temperature changes of these discrete bodies could reverse crystallization and viscous lock-up and propel magma toward a crystal-poor eruptible state.

Madagascar hosts several Paleoproterozoic sedimentary sequences that are key to unravelling the geodynamic evolution of past supercontinents on Earth. New detrital zircon U–Pb and Hf data, and a substantial new database of ~15,000 analyses are used here to compare and contrast sedimentary sequences in Madagascar, Africa and India. The Itremo Group in central Madagascar, the Sahantaha Group in northern Madagascar, the Maha Group in eastern Madagascar, and the Ambatolampy Group in central Madagascar have indistinguishable age and isotopic characteristics. These samples have maximum depositional ages > 1700 Ma, with major zircon age peaks at c. 2500 Ma, c. 2000 Ma and c. 1850 Ma. We name this the Greater Itremo Basin, which covered a vast area of Madagascar in the late Paleoproterozoic. These samples are also compared with those from the Tanzania and the Congo cratons of Africa, and the Dharwar Craton and Southern Granulite Terrane of India. We show that the Greater Itremo Basin and sedimentary sequences in the Tanzania Craton of Africa are correlatives. These also tentatively correlate with sedimentary protoliths in the Southern Granulite Terrane of India, which together formed a major intra-Nuna/Columbia sedimentary basin that we name the Itremo-Muva-Pandyan Basin. A new Paleoproterozoic plate tectonic configuration is proposed where central Madagascar is contiguous with the Tanzania Craton to the west and the Southern Granulite Terrane to the east. This model strongly supports an ancient Proterozoic origin for central Madagascar against the Tanzania Craton of East Africa.

Bedrock river lateral erosion plays a crucial role in landscape evolution, sediment transport and deposition, and the occurrence of geohazards. Lateral erosion is driven by the impacts of bedload particles (BPs). However, BPs generally move parallel to the channel walls and thus need to be deflected sidewards to cause wall erosion. Sideward deflection of BPs occurs when they interact with roughness elements (REs) fixed on the riverbed. We set up 21 sets of flume experiments to systematically investigate how spacing (5, 10, 20, 30, 40, 50, and 60 mm) and size (5, 10, and 20 mm) of REs influence sideward deflection of BPs. The deflection length and speed peaks at intermediate values of the spacing of REs. The likelihood for a BP to leave the roughness zone decays with the BP’s distance to its edge. Our results suggest that lateral erosion rates in bedrock channels are dominantly controlled by the position of the roughness zone within the channel and its relation to the particle path.

The unsaturated zone serves as reservoir for geogenic and anthropogenic contaminants to local groundwater. Biogeochemical processes in this zone can be affected by nitrogen and water infiltration mobilizing contaminants, ultimately affecting groundwater quality. In this large-scale study, we evaluated the effects of estimated water and nitrogen inputs to the unsaturated zone of a public water supply wellhead protection (WHP) area with respect to subsurface occurrence and transport of nitrate, ammonium, arsenic, and uranium. Thirty-two coring sites were sampled and grouped by water application volume, irrigated – sprinkler (n=20), gravity (n=4) and non-irrigated land use. Unsaturated zone sediments were evaluated for the potential to mobilize arsenic and uranium in relation to nitrogen and water use. Sediment nitrate and ammonium had strong significant (p<0.05) correlation under all water application. Nitrate concentrations were lower beneath sprinkler-irrigated sites but had statistically higher ammonium concentrations than gravity-irrigated. Sediment nitrate concentrations were significantly (p<0.05) different among water application types, suggesting a strong effect of water volume on the changing nitrate concentration. Sediment arsenic presumably attenuated by iron (r=0.32 p<0.05). Uranium in sediments of unsaturated zone was negatively correlated to increase in sediment nitrate (r=-0.23 p<0.05) and ammonium (r=-0.19 p<0.05). Water application types were found to significantly influence sediment arsenic and uranium. While the groundwater arsenic and uranium concentration were below maximum contaminant levels, the highest uranium concentrations were observed in samples from WHP area. The study suggests that irrigation has an impact on unsaturated zone geochemistry with the potential to ultimately affect groundwater quality.