October 9, 2015
Geologic Map of the Masters 7.5' Quadrangle, Weld and Morgan Counties, Colorado
By Margaret Berry (GECSC), Janet Slate, Jim Paces (GECSC), Paul Hanson, and Ted Brandt (GECSC). U.S. Geological Survey Scientific Investigations Map 3344.
The Masters 7.5' quadrangle is located along the South Platte River corridor on the semiarid plains of eastern Colorado. The mapped area contains surficial deposits that record alluvial, eolian, and hillslope processes that have operated in concert with environmental changes from Pleistocene to present time. Along with the map and georeferenced map PDFs, this publication includes downloadable GIS files, and an appendix detailing the U-series analyses and resultant 230Th/U ages that support the geologic map.
October 8, 2015
Effects of rapid urbanization on streamflow, erosion, and sedimentation in a desert stream in the American Southwest
By John Whitney (GECSC), Patrick Glancy, Susan Buckingham, and Arthur Ehrenberg. Published in Anthropocene.
This study describes the effects of rapid urban growth and development on a dry desert wash in the arid-semiarid region of Las Vegas Valley in southern Nevada. Increased wastewater flow from constantly increasing population growth during the late 20th century has resulted in accelerated erosion in Lower Las Vegas Wash; a dry wash otherwise characterized by infrequent flood erosion and deposition. Initial wastewater discharge created floodplain wetlands; however, increasing baseflow and storm runoff resulted in erosion that continued unabated until engineering interventions began in the 21st century. A 6.6 million cubic meter sediment slug was eroded from the wash and deposited in Las Vegas Bay in Lake Mead over ~25 years. This is the largest measured volume of erosion related to urbanization in the U.S.; it resulted in infrastructure losses, had a strong environmental impact on Lake Mead, and required a costly program of channel stabilization, flood protection and wetlands restoration. Drought conditions since 1999 are responsible for historic low lake levels and the infilling of Las Vegas Bay by redistribution of the wash delta sediments.
October 1, 2015
Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes
By P.J. Bartlein, M.E. Edwards, S.W. Hostetler, Sarah Shafer (GECSC), P.M. Anderson, L.B. Brubaker, and A.V. Lozhkin. Published in Climate of the Past.
Recent climate changes are affecting arctic ecosystems and generating land cover changes, such as expansion of woody vegetation into tundra, that may produce feedbacks to the climate system. To better understand the mechanisms controlling these feedbacks, this study used a regional climate model to simulate the effects of arctic land cover changes in Beringia (northeastern Siberia, Alaska, and northwestern Canada) ~11,000 years ago, focusing on the climate feedbacks produced by sea-level rise (e.g., flooding of the Bering-Chukchi land bridge), changes from tundra to deciduous broadleaf woody vegetation, and the formation of thaw lakes. Sea-level rise produced the largest climate effect (cooler summers, warmer winters), while vegetation changes produced warming in spring and early summer, and thaw lakes produced localized cooling in summer and warming in winter.