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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]

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]

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]

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]

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]