Geology topics

L. V. Benson

Publications and source records attributed to L. V. Benson.

23 records · Page 2Linked to original sources

USGS1990

Paleoclimatic implications of the high stand of Lake Lahontan derived from models of evaporation and lake level

Based on previous climate model simulations of a split of the polar jet stream during the late Pleistocene, we hypothesize that (1) 20-13.5 ka BP, season-to-season variation in the latitudinal maximum of the jet stream core led to enhanced wetness in the Great Basin, and (2) after 13.5 ka BP, northward movement of the jet stream resulted in increased aridity similar to today. We suggest that the enhanced effective wetness was due to increased precipitation combined with an energy-limited reduction in evaporation rates that was caused by increased summer cloud cover. A physically based thermal evaporation model was used to simulate evaporation for Lake Lahontan under various hypothesized paleoclimates. The simulated evaporation rates, together with hypothetical rates of precipitation and discharge, were input to a water balance model of Lake Lahontan. A 42% reduction in evaporation rate, combined with maximum historical rates of precipitation (1.8 times the mean annual rate) and discharge (2.4 times the mean annual rate), were sufficient to maintain Lake Lahontan at its 20-15 ka BP level. When discharge was increased to 3.8 times the present-day, mean annual rate, the ??? 13.5 ka BP maximum level of Lake Lahontan was attained within 1400 years. A 135-m drop from the maximum level to Holocene levels was simulated within 300 years under the imposition of the present-day hydrologic balance. ?? 1990 Springer-Verlag.

Climate Dynamics↗

USGS1990

Chronology of expansion and contraction of four great Basin lake systems during the past 35,000 years

During the past 35,000 years, Lake Bonneville, Lake Russell, and Lake Searles underwent a major period of lake-level change. The lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15,000 and 13,500 yr B.P. The rise of Lake Lahontan was gradual but not continuous, in part because of topographic constraints (intrabasin spill). Lake Lahontan also had an oscillation in lake level at 15,500 yr B.P. Radiocarbon-age estimations for materials that were deposited in the lake basins indicate that Lake Bonneville rose more or less gradually from 32,000 yr B.P., and had major oscillations in level between 23,000 and 21,000 yr B.P. and between 15,250 and 14,500 yr B.P. Lake Russell and Lake Searles had several major oscillations in lake level between 35,000 and 14,000 yr B.P. The timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states. All four lakes may have had nearly synchronous recessions between about 14,000 and 13,500 yr B.P. After the recessions, the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11,500 and 10,000 yr B.P. These data provide circumstantial evidence that the Younger Dryas Event affected climate on at least a hemispheric scale. During the Holocene, the four lakes remained at low levels, and small oscillations in lake level occurred. An important aspect of the lake-level data is the accompanying expansion of lake-surface area at the time of the last highstand. Lake Bonneville and Lake Lahontan had surface areas about 10 times larger than their mean-historical reconstructed areas whereas Lake Russell and Lake Searles had surface areas about 5 times larger than their mean-historical reconstructed areas. Differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream, or they may have resulted from lake/atmosphere feedback processes.

California, Idaho, Nevada, Oregon↗

USGS1985

Chemical composition of ground water in the Yucca Mountain area, Nevada, 1971-84

Fifteen wells in the Yucca Mountain area of southern Nevada have been sampled for chemical analysis. Samples were obtained by pumping water from the entire well bore (composite sample), and, in three instances, by pumping from one or more isolated intervals within a well bore. Sodium is the most abundant cation , and biocarbonate is the most abundant anion in all water samples. Samples from the Paleozoic carbonate aquifer penetrated by well UE-25p 1 contain higher relative concentrations of calcium and magnesium than samples from overlying volcanic tuffs. Values of the stable isotope concentrations of oxygen and hydrogen are relatively negative (light) and have deuterium excess values ranging from +5 to +10. The distribution of uncorrected radiocarbon ages of tuffaceous groundwater from samples within one kilometer of the exploratory block ranges from 12,000 to 18,500 years before present. Variation in the inorganic, stable, and radioactive isotope composition of samples indicates a significant degree of lateral and vertical chemical inhomogeneity in groundwater of the Yucca Mountain area. (USGS)

Open-File Report↗

USGS1983

Chemical composition of ground water and the locations of permeable zones in the Yucca Mountain area, Nevada

Ten wells in the Yucca Mountain area of southern Nevada have been sampled for chemical analysis. Samples were obtained during pumping of water from the entire well bore (composite sample) and in one instance by pumping water from a single isolated interval in well UE-25b number 1. Sodium is the most abundant cation and bicarbonate the most abundant anion in all water samples. Although the general chemical compositions of individual samples are similar, there are significant differences in uncorrected carbon-14 age and in inorganic and stable-isotope composition. Flow surveys of seven wells performed using iodine-131 as a tracer indicate that groundwater production is usually from one or more discrete zones of permeability. (Author 's abstract)

Open-File Report↗

USGS1979

Uranium transport in the Walker River Basin, California and Nevada

During the summer of 1976 waters from tributaries, rivers, springs and wells were sampled in the Walker River Basin. Snow and sediments from selected sites were also sampled. All samples were analyzed for uranium and other elements. The resulting data provide an understanding of the transport of uranium within a closed hydrologic basin as well as providing a basis for the design of geochemical reconnaissance studies for the Basin and Range Province of the Western United States. Spring and tributary data are useful in locating areas containing anomalous concentrations of uranium. However, agricultural practices obscure the presence of known uranium deposits and render impossible the detection of other known deposits. Uranium is extremely mobile in stream waters and does not appear to sorb or precipitate. Uranium has a long residence time (2500 years) in the open waters of Walker Lake; however, once it crosses the sediment-water interface, it is reduced to the U(IV) state and is lost from solution. Over the past two million years the amount of uranium transported to the terminal point of the Walker River system may have been on the order of 4 × 10 8 kg . This suggests that closed basin termini are sites for significant uranium accumulations and are, therefore, potential sites of uranium ore deposits.

Journal of Geochemical Exploration↗