Geology topics

G.J. Leonard

Publications and source records attributed to G.J. Leonard.

3 recordsLinked to original sources

USGS2016

Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake

The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes’ induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions.

Science↗

USGS1988

Hydrogeology and simulated effects of ground-water development on an unconfined aquifer in the Closed Basin Division, San Luis Valley, Colorado

Wells completed in an unconfined aquifer in the Closed Basin Division of the San Luis Valley Project, Colorado, are expected to provide about 101,800 acre-ft of groundwater/year to the Rio Grande when this project is completed. Lowering of groundwater levels in the unconfined aquifer is expected to decrease the quantity of groundwater that is lost by evapotranspiration. The aquifer system, which consists of an unconfined aquifer that is 50 to 130 ft thick, overlies a thick, leaky confined aquifer. Groundwater moves from the edge of the valley toward a topographic low near the center of the Closed Basin Division, where it is lost by evapotranspiration. A two-dimensional groundwater flow model was used to evaluate the effects of projected withdrawal of about 141 cu ft/sec by 168 wells throughout a 20-year period. The simulated pumpage resulted in a projected drawdown greater than 0.1 ft in the water-levels of the unconfined aquifer over an area of about 370 sq mi. Maximum simulated drawdown was 25 ft. Simulations indicate that about 66 % of the water to be withdrawn from the unconfined aquifer would be derived from decreases of evapotranspiration, 26% from induced leakage from an underlying confined aquifer, and 8% from storage of the unconfined aquifer. Model simulations were based only on withdrawals from wells completed in the unconfined aquifer. Pumpage from the confined aquifer was not simulated. Upward leakage from the confined aquifer predicted by the model, results from the simulated declines of the potentiometric surface in the unconfined aquifer. (USGS)

Water-Resources Investigations Report↗

USGS1984

Assessment of water resources at Fort Carson Military Reservation near Colorado Springs, Colorado

The Fort Carson Military Reservation adjoins the rapidly growning Colorado Springs metropolitan area, where locally available water supplies are limited and strictly administered. Fort Carson purchases about 3,400 acre-feet of treated water annually from the city of Colorado Springs. The major streams entering Fort Carson have an estimated average annual discharge of 6,240 acre-feet of water per year upstream from diversions for municipal and domestic water supplies. The streamflow is unevenly distributed in time and consequently not dependable as a large or sole source of water. Ground water is available from alluvial and bedrock aquifers. Wells with yields greater than 100 gallons per minute can be expected from the alluvium along Rock and Little Fountain Creeks and from some parts of the Dakota-Purgatoire aquifer. The quality of surface water entering Fort Carson is generally suitable for irrigation and drinking but deteriorates eastward across Fort Carson. Water from the alluvial aquifer along Rock and Little Fountain Creeks in the eastern part of Fort Carson contains fluoride in concentrations exceeding drinking-water standards. Water from the Dakota-Purgatoire aquifer characteristically contains radiochemical constituents in concentrations that exceed drinking-water standards. (USGS)

Water-Resources Investigations Report↗