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We examine the coseismic influence of the 5 July 2019, MW7.1 Ridgecrest and the 24 June 2020 MW5.8 Owens Lake earthquakes on rockfall distributions in two undisturbed high-altitude areas of the southern Sierra Nevada Mountains, California, USA. These events occurred within the geologically recent (<2 Mya) Walker Lane/eastern California shear zone. While both study areas are characterized as plutonic, the Owens Lake event largely affected terrain that was formerly glaciated and oversteepened while the Ridgecrest event affected non-glaciated terrain. Our inventory of rockfall locations was derived from analysis of Sentinel-2 images acquired just prior to and immediately after the events. This difference mapping approach using readily-available Sentinel-2 imagery allows for rapid rockfall and landslide mapping. GIS analysis shows that even though the total area assessed for both earthquakes was similar (~1500 km2), the significantly lower magnitude Owens Lake event produced nearly twice as many (102) mappable rockslides as the significantly stronger Ridgecrest event (58), a difference likely due to slope oversteepening in the formerly glaciated area. Significant seismic amplification by topography and reactivation of preexisting failures was apparent for both areas. Inclusion of these factors may improve failure predictions and rockfall probability estimation. [ABSTRACT FROM AUTHOR]

Data analysis methods have scarcely kept pace with the rapid increase in Earth observations, spurring the development of novel algorithms, storage methods, and computational techniques. For scientists interested in Mars, the problem is always the same: there is simultaneously never enough of the right data and an overwhelming amount of data in total. Finding sufficient data needles in a haystack to test a hypothesis requires hours of manual data screening, and more needles and hay are added constantly. To date, the vast majority of Martian research has been focused on either one-off local/regional studies or on hugely time-consuming manual global studies. Machine learning in its numerous forms can be helpful for future such work. Machine learning has the potential to help map and classify a large variety of both features and properties on the surface of Mars and to aid in the planning and execution of future missions. Here, we outline the current extent of machine learning as applied to Mars, summarize why machine learning should be an important tool for planetary geomorphology in particular, and suggest numerous research avenues and funding priorities for future efforts. We conclude that: (1) moving toward methods that require less human input (i.e., self- or semi-supervised) is an important paradigm shift for Martian applications, (2) new robust methods using generative adversarial networks to generate synthetic high-resolution digital terrain models represent an exciting new avenue for Martian geomorphologists, (3) more effort and money must be directed toward developing standardized datasets and benchmark tests, and (4) the community needs a large-scale, generalized, and programmatically accessible geographic information system (GIS). [ABSTRACT FROM AUTHOR]

The presence of buried glacial ice and putative extinct rock glaciers in Mars' equatorial regions has implications for understanding its climate history and sensitivity to changes in insolation and has significant implications for past global redistribution of the water ice cryosphere. We quantify the morphology of rock glacier- "like" features on the northern slopes of Aeolis Mons (known also as Mount Sharp) within Gale crater and use this information to evaluate a possible rock glacier origin for these forms. Detailed morphometric evaluation of cross and long profiles of these lobate features, which exhibit higher slopes at their heads, lower slopes at their distal edge, and a convex upward cross-sectional profile and oversteepened sides, resembles active terrestrial rock glaciers. However, the absence of a chevron wrinkle pattern and sublimation features could indicate extensive aeolian reworking and the lack of deflation could indicate a higher rock to ice mixture. The lack of cratering surfaces relative to the cratered surfaces that they overly could indicate a younger age and are possibly indistinguishable in age from the capping units of Mount Sharp, which may have once been more laterally extensive and may have been the source of these mass wasting forms. [ABSTRACT FROM AUTHOR]

The use of process based geographic information systems for decisions on water reallocation is discussed. These use biophysical, institutional and information for more accurate assessments of the impact of such decisions.

The Hunshandake Sandy Lands of northeastern China, currently a semiarid lightly vegetated region, were characterized by perennial lakes and forest stands in the early and middle Holocene. Well-developed dark grassland-type paleosols (mollisols) at the southern edge of the Hunshandake – OSL (optically stimulated luminescence)-dated to between 6.93±0.61 and 4.27±0.38 ka along with lacustrine sands at higher elevations that date to between 5.7±0.3 and 5.2±0.2 ka – and thick gray lacustrine sediments suggest a wetter climate. Between 4.2 and 3.8 ka, the region experienced extreme drying that was exacerbated by lake overflow drainage and sapping that depleted the groundwater table. The region supported a robust population, the Hongshan Culture, but was depopulated post 4.2 ka with migration likely to the Yellow River Valley where the Hongshan introduced their characteristic cultural elements to early Chinese civilization. Evidence for extreme and sudden environmental change in northeastern China, at and following the 4.2 ka BP Event and like that we document in the Hunshandake, is widespread. However, no comprehensive overview of this climatic episode exists. Here, we discuss the relevant events in northeastern China and capture them in a spatially explicit Geographic Information Systems database that can be used to analyze the timing and spatial pattern of climate and environmental change associated with the 4.2 ka BP Event. This approach could serve as a prototype for a global 4.2 ka BP Event database. [ABSTRACT FROM AUTHOR]

The Hunshandake Sandy Lands of northeastern China, currently a semi-arid lightly-vegetated region, were characterized by perennial lakes and forest stands in the early and middle Holocene. Well-developed dark grassland-type paleosols (mollisols) at the southern edge of the Hunshandake, OSL-dated to between 6.93 ± 0.61 and 4.27 ± 0.38 cal ka BP along with lacustrine sands in higher elevations that date to between 5.7 ± 0.3 and 5.2 ± 0.2 cal ka BP, and thick gray lacustrine sediments suggest a wetter climate. Between 4.2 and 3.8 cal ka BP the region experienced extreme drying that was exacerbated by headwater cutting of the overflow drainage that depleted the groundwater table through sapping. The region supported a robust population, the Hongshan Culture. The region depopulated post-4.2 cal ka BP and its people migrated out of the region, likely to the Yellow River Valley where they introduced their characteristic cultural elements to early Chinese civilization. Evidence for extreme and sudden environmental change in northeastern China, at and following the 4.2 cal ka BP event and like that we document in the Hunshandake, is widespread. However, no comprehensive overview exists. Here we discuss the relevant events in northeastern China and capture them in a spatially explicit Geographic Information Systems database that can be used to analyze the timing and spatial pattern of climate associated with the 4.2 cal ka BP event. This approach could serve as a prototype for a Global 4.2 cal ka BP event database. [ABSTRACT FROM AUTHOR]

Abstract: Characterization of dune morphology has historically been based on relationships between dune forms and wind regimes with dune height shown to be sensitive to atmospheric boundary layer depth, sand availability and sediment properties. While these parameters have been used in numerical simulations to model the occurrences of some types of dunes, they cannot alone explain the great diversity in form and size seen on Earth and on other solar system bodies. Here we present results from our studies of dune formation in the Badain Jaran Desert in western China, where Earth''s tallest dunes occur. We measured the variability of the dune morphology in this desert on the basis of LANDSAT ETM+ data, and we detected the bedrock landforms beneath the aeolian sands by applying gravity methods. Wind records from stations at the periphery of the desert and SRTM topographical data were examined also to augment the interpretation. Our studies demonstrate that in addition to average wind parameters, dune height is highly sensitive to local geology, subsurface characteristics, and topography, and interactions between changing climate conditions and aeolian and fluvial processes. These additional factors need to be considered in the interpretation and simulation of dunes on Earth. We anticipate that analysis of anomalous dune heights like those seen in the Badain Jaran may also provide critical information on subsurface characteristics and environmental conditions on Earth and on other planetary bodies. [Copyright &y& Elsevier]

Transverse aeolian ridges (TARs) are poorly understood relict aeolian Martian surface features. Processes that create TARs are not well-constrained, and understanding their formation is complicated since they appear to share some features of ripples, megaripples, and dunes. While some evidence of multi-stage TAR formation has been documented in Nirgal Vallis, here we present additional evidence for this process at nine locations on Mars using cratering superposition between different ridge morphologies. Most occurrences of multistage evolution will not preserve the precise series of cratering and formation events documented here, which potentially means that this formative process may have been more common than even these new widespread observations suggest. This formative process can help determine the relative similarity of TARs to ripples, megaripples and dunes. Based on our observations, we conclude that primary TAR forms are most like megaripples, and that subsequent ridges formed like aqueous ripple spurs. [ABSTRACT FROM AUTHOR]

Atmospheric Rivers (AR) are narrow bands of water vapor transport, responsible for 90% of mid-latitude water transportation as well as intense and prolonged precipitation events. In the late 1861-1862 an AR event produced flooding that caused a magnitude of economic impacts. We hypothesize that precipitation from these events produces a change in the response of both high-altitude temperature sensitive trees and low-altitude precipitation sensitive trees and that these responses can be used to quantify this event. We created normalized growth indexes for each individual tree ring record and correlated the growth with factors such as altitude and species to quantify the growth. Analysis of the mapped tree growth response is used to extract a coherent signal that may be representative of AR events in general. This signal could then be used to determine if similar extreme AR events occur in earlier portions of the tree ring record. Analysis of this dataset will allow us to better understand, monitor and predict the impact of large AR events on California. The frequency and strength of AR events impacts the length of droughts, intensity of floods, ecosystem response and ultimately impacts on humans. [ABSTRACT FROM AUTHOR]

Transverse aeolian ridges (TARs) are unusual bedforms on the surface of Mars. TARs are common but sparse on Mars; TAR fields are small, rarely continuous, and scattered, making manual mapping impractical. There have been many efforts to automatically classify the Martian surface, but they have never explicitly located TARs successfully. Here, we present a simple adaptation of the off-the-shelf neural network RetinaNet that is designed to identify the presence of TARs at a 50-m scale. Once trained, the network was able to identify TARs with high precision (92.9%). Our model also shows promising results for applications to other surficial features like ripples and polygonal terrain. In the future, we hope to apply this model more broadly and generate a large database of TAR distributions on Mars. [ABSTRACT FROM AUTHOR]

Convergence and shallow subduction of the Yakutat microplate beneath North America has shaped the Pamplona zone fold and thrust belt in the northeastern Alaska subduction zone. Here, convergent tectonics and glaciomarine sedimentary processes have created patterns of deformation and deposition recorded by a shallow sedimentary sequence with varying fluid pressure, compaction, and fault activity. If the record of ice sheet advance is preserved on the seafloor and in the underlying sediments then bathymetric evidence of glaciomarine processes should overlap with evidence of overpressure, such as low velocity zones in the shallow sediments. In this study, we present a velocity model through the Bering trough as well as regional drainage shape characteristics. We use streamer tomography on a seismic survey from the St. Elias Erosion and Tectonics Project (STEEP) to determine a velocity model. We further inform our interpretation using physical properties relationships developed with data from core samples (IODP Expedition 341) taken near the seismic line. To document drainage morphology, we use smooth sheet bathymetry to identify a drainage network and query profile shapes at well distributed locations; where profile shape is determined by fit with a power function. Initial results suggest overlap between u-shaped drainage profiles towards the SE end of the Bering trough and low-velocity shallow sediments NE of the shelf break. In part, because this overlap occurs within the mapped extent of the last glacial maximum, we find our tomography results consistent with buildup of overpressure due to glacially driven loading of highly saturated sediments. [ABSTRACT FROM AUTHOR]

Linear dunes and human fingerprints share many characteristics. Both have ridges, valleys, and defects (minutiae) in the form of bifurcations and termination of ridgeline features. For dunes, determining how defects vary across linear and transverse dunefields is critical to understanding the physics of their formative processes and the physical forcing mechanisms that produce dunefields. Unfortunately, manual extraction of defect locations and higher order characteristics (type, orientation, and quality) from remotely sensed imagery is both time-consuming and inconsistent. This problem is further exacerbated when, in the case of imagery from sensors in orbit around Mars, we are unable to field check interpretations. In this research, we apply a novel technique for extracting defects from multiple imagery sources utilizing a robust and well-documented fingerprint minutiae detection and extraction software (MINDTCT: MINutiae DecTeCTion) developed by the National Institute of Standards and Technology (NIST). We apply our 'fingerprinting' approach to Transverse Aeolian Ridges (TARs), relict aeolian features commonly seen on the surface of Mars, whose depositional and formative processes are poorly understood. Our algorithmic approach demonstrates that automating the rapid extraction of defects from orbitally-derived high-resolution imagery of Mars is feasible and produces maps that allow the quantification and analysis of these features. [ABSTRACT FROM AUTHOR]

Understanding the subsurface hydrology, or ground water elevation, of arid environments like large dune forming deserts, is critical to sustaining habitable zones during times of rapid climate change. The tallest dunes and largest sand sea in the solar system is located on Earth, in China's Badain Jaran Desert. The Badain Jaran Desert provides a unique study area because it has been inhabited by human populations since prehistoric times, and provides a unique opportunity to utilize both geologic and archaeological evidence for indicators of Quaternary climate change over the past 5,000 years. We hypothesize that the decrease in water table elevation reflected in modern interdune lakes is a result of Quaternary climate change, transforming the region from wetlands to an arid dune complex. Although this area has a rich archaeological record, limited studies have been conducted to understand the modern water table elevation and its change through recent Earth history. Using satellite imagery and geospatial processing and analyzing tools such as ArcGIS and Google Earth, the modern ground water elevation was traced within the dune field and compared to ancient lake core sediment samples. The samples were radio-carbon dated to compare the rate of change in ground water elevation over the past 5,000 years. Utilizing the archaeological record within the study area, we compared the change in human populations within the region to the change in water resources over time and found a relationship between population decrease and a decrease in ground water elevation within the Quaternary. [ABSTRACT FROM AUTHOR]

Gliese 569B is a multiple brown dwarf system whose exact nature has been the subject of several investigations over the past few years. Interpretation has partially relied on infrared photometry and spectroscopy of the resolved components of the system. We present seeing-limited Ks photometry over four nights, searching for variability in this young low-mass substellar system. Our photometry is consistent with other reported photometry, and we report the tentative detection of several periodic signals consistent with rotational modulation due to spots on their surfaces. The five significant periods range from 2.90 hr to 12.8 hr, with peak-to-peak variabilities from 28 mmag to 62 mmag in the Ks band. If both components are rotating with the shortest periods, then their rotation axes are not parallel with each other, and the rotation axis of the Bb component is not perpendicular to the Ba-Bb orbital plane. If Bb has one of the longer rotational periods, then the Bb rotation axis is consistent with being parallel to the orbital axis of the Ba-Bb system. [ABSTRACT FROM AUTHOR]

Meandering fluvial channels and their meander belts are common in modern continental sedimentary basins, yet compose a minor constituent of the reported fluvial rock record. Here we document exhumed amalgamated meander belt deposits from the upper Jurassic Morrison Formation, Utah (United States). The size of the amalgamated meander belt (9000 km²) is significantly larger than any documented previously and comparable in size to those from modern sedimentary basins. We describe a representative outcrop of sandy point bar deposits that shows features considered characteristic of both braided and meandering fluvial systems. Lateral accretion sets compose <5% of the outcrop area, yet point bar morphology is clearly visible in plan view. We suggest that difficulties in the identification of sandy, amalgamated meander belt deposits indicate that they have gone largely unrecognized in the rock record. Their recognition has important implications for basin-scale reconstructions of fluvial systems and interpretation of tectonic setting. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of over 400 fluvial megafans (>30km in length) in aggradational continental sedimentary basins reveals that geomorphic channel and floodplain changes on these distributive fluvial systems (DFS) generally behave in predictable ways with increasing distance from the apex. These changes can include: a decrease in discharge, a decrease in bed material transport and calibre of sediment, a decrease in stream power, an overall decrease in channel width, an overall decrease in channel depth, an increase in avulsive behaviour, and sinuosity becomes more variable. Three generic geomorphic element models are proposed – reflecting observed changes in channel behaviour – based on measurable changes in channel width and planform characteristics with increasing distance downstream. The three models are derived from (1) a single braided channel that bifurcates downstream into low sinuosity channels; (2) a dominant, sinuous, single-thread channel that anabranches and bifurcates with distance downstream, creating smaller channels with varying sinuosity; and (3) a dominant multi-thread channel that anabranches and bifurcates with distance downstream, creating smaller channels with varying sinuosity. The changes in fluvial behaviour and landforms on DFS are in response to variable discharge and sediment supply ratios from the upstream catchment. In contrast to examples described in hydrogeomorphological literature for tributary fluvial systems where channel dimensions tend to increase downstream, observations from DFS suggest that – where the formative DFS channel does not retain the same dimensions – intrinsic geomorphic thresholds lead to the breakdown of the main trunk channel into smaller anabranching and distributary channels with distance downstream; in some instances the majority of channelised flow at the DFS termination may even be disintegrated. The observed range of termination types and floodplain soils for each DFS type are interchangeable dependent on local conditions. The modern geomorphic elements and floodplain soils are dependent on climate in the upstream catchment and in the downstream receiving sedimentary basin. [Copyright &y& Elsevier]

Abstract: The formation of cracks is a fundamental first step in the physical weathering of rocks in desert environments. In this study we combine new field data from the Mojave (U.S.), Gobi (Mongolia) and Strzelecki (Australia) deserts that collectively support the hypothesis that meridional cracks (cracks with orientations not readily attributable to rock anisotropies or shape) in boulders or cobbles form due to tensile stresses caused by directional heating and cooling during the sun''s daily transit. The new studies indicate that rock size, surface age, and latitude play important roles with respect to their influence on rock fracture. Rock size and pavement surface age exert an influence on the development of rock cracks as the average clast size of mature desert pavements may be at or below the threshold-clast size for thermal cracking of rocks. Latitude-controlled seasonal temperature variations play a key role, as demonstrated by: 1) tightly clustered mean resultant orientations that differ by latitude, as predicted in McFadden et al. (2005), and 2) very cold wintertime temperatures and strong diurnal gradients that may favor crack development in wintertime, given the likelihood for strong clast heating during early morning hours. The consistent evidence for meridional cracks in surfaces of diverse age and desert environments, climate, vegetation, and distance of clast transport indicate that directional insolation may play the key role in initially generating and propagating rock fractures, rather than a secondary role as implied in recent field and modeling studies of physical weathering in deserts. [Copyright &y& Elsevier]

The advent of high-resolution, precise, back-pack portable terrestrial lidar scanners (TLS) provides a revolutionary new tool for obtaining quantitative, high-resolution (2-mm to 30-mm point spacing) measurements of landscape surface features. Moreover, data collected using these instruments allow observation of geomorphic processes in systems that can experience change on a daily basis. We have introduced TLS techniques in ongoing investigations of semiarid landscapes associated with weakly cemented sandstones along part of the Black Mesa escarpment of NE Arizona. Clay-cemented, Jurassic sandstones exposed along this escarpment are sensitive to moisture, and thus climate, via hydration-expansion weathering of interstitial clay. Sediment shed from weathered slopes has caused locally rapid valley floor aggradation and upper basin slope vertical denudation rates of 2–3 mm/yr over 10- to 100-yr timescales, as indicated by dendrochronology coupled with soil geomorphic analysis. These rates suggest rapid hillslope denudation rates. Employing the University of New Mexico Lidar Laboratory Optech Ilris 3D TLS, we are constructing a high-resolution model of two major basins along the escarpment. Focusing on a single, small (30 × 60 m) area of a mostly non-vegetated, steep slope (>35°), we demonstrate in this paper a method of comparative analysis of pointcloud data sets that can detect subcentimeter change resulting from a single season of monsoon precipitation along the escarpment. Using repeat scans can provide an empirical evaluation of single season erosion rates in the study site, and because our observations are geospatial in nature, we can also document the parts of the slopes that make the greatest contribution to local valley floor aggradation. In demonstrating the utility of this method, we expect that continued investigation of this site will provide insight to the key processes associated with soil-mantled versus bedrock-dominated slopes during modern escarpment retreat and hillslope modification, which, in turn, may further elucidate the impacts of Holocene climate change on this rapidly evolving landscape. [ABSTRACT FROM AUTHOR]