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James B. Gillespie

Publications and source records attributed to James B. Gillespie.

4 recordsLinked to original sources
USGS2014

Eruptive and tectonic history of the Endeavour Segment, Juan de Fuca Ridge, based on AUV mapping data and lava flow ages

High-resolution bathymetric surveys from autonomous underwater vehicles ABE and D. Allan B. were merged to create a coregistered map of 71.7 km2 of the Endeavour Segment of the Juan de Fuca Ridge. Radiocarbon dating of foraminifera in cores from three dives of remotely operated vehicle Doc Ricketts provide minimum eruption ages for 40 lava flows that are combined with the bathymetric data to outline the eruptive and tectonic history. The ages range from Modern to 10,700 marine-calibrated years before present (yr BP). During a robust magmatic phase from >10,700 yr BP to ~4300 yr BP, flows erupted from an axial high and many flowed >5 km down the flanks; some partly buried adjacent valleys. Axial magma chambers (AMCs) may have been wider than today to supply dike intrusions over a 2 km wide axial zone. Summit Seamount formed by ~4770 yr BP and was subsequently dismembered during a period of extension with little volcanism starting ~4300 yr BP. This tectonic phase with only rare volcanic eruptions lasted until ~2300 yr BP and may have resulted in near-solidification of the AMCs. The axial graben formed by crustal extension during this period of low magmatic activity. Infrequent eruptions occurred on the flanks between 2620–1760 yr BP and within the axial graben since ~1750 yr BP. This most recent phase of limited volcanic and intense hydrothermal activity that began ~2300 yr BP defines a hydrothermal phase of ridge development that coincides with the present-day 1 km wide AMCs and overlying hydrothermal vent fields.

Geochemistry, Geophysics, Geosystems↗
USGS1988

Channel infiltration from floodflows along the Pawnee River and its tributaries, west-central Kansas

Most of the streams is west-central Kansas are ephemeral. Natural recharge to the alluvial aquifers underlying these streams occurs during periods of storm runoff in the ephemeral channels. Proposed flood-retarding structures within the basin will alter the downstream runoff characteristics in these channels by reducing the peak flow and increasing the flow duration. Information concerning channel-infiltration rate, unsaturated and saturated flow, and lithology of the unsaturated zone as related to stream stage and duration was collected along the Pawnee River and its tributaries to determine the effects of the flood-retarding structures. The infiltration rate on ephemeral streams was determined at five sites within the Pawnee River Basin. Tests were conducted in channel infiltrometers constructed by isolating a section of channel with two plastic-lined wooden cofferdams. At two of the sites, perched groundwater mounds intersected the bottom of the channel and reduced the infiltration rate. At two other sites where the perched groundwater mounds did not reach the bottom of the channel, the infiltration rate was directly proportional to the stage. Comparison of infiltration from simulated controlled and uncontrolled floodflows at the five sites indicated an average increase of about 2% with the controlled floodflow. Cumulative infiltration for these simulations ranged from 0.5 to 14.8 acre-ft/mi of channel. (USGS)

Water-Resources Investigations Report↗
USGS1985

Ground-water flow and solute transport in the Equus beds area, south-central Kansas, 1940-79

Water levels have declined about 30 ft from 1940 to 1980 in part of the Equus beds aquifer in south-central Kansas where the city of Wichita operates a well field. A three-dimensional, finite-difference, groundwater flow model was developed to: (1) Reproduce hydrologic conditions in the flow system between the Equus beds aquifer and the underlying Wellington aquifer from 1940 to 1980, and (2) simulate the effect that future withdrawals could have on water supply in the Equus beds aquifer and on relationships between water levels in the Equus beds aquifer and the Wellington aquifer from 1980 to 2020. The model favorably reproduced both measured water levels and streamflow gains in the Equus beds aquifer for 1971 and 1980, and measured water levels in the Wellington aquifer. The flow model then was used to simulate the effects of five pumping alternatives based on rates of withdrawal by wells from 1971-79. For the first alternative, withdrawal rates were decreased by one-half. Projected saturated thickness in the aquifer and streamflow gain were the greatest among the five alternatives. For the second alternative, withdrawal rates for 1971-79 were continued. Compared to results from the first alternative, saturated thickness was projected to decline from 10 to 40 ft in some areas, and streamflow gains were maintained for the Arkansas and Little Arkansas Rivers. A two-dimensional, finite-difference, solute-transport model was developed to: (1) Reproduce the movement of chloride ion in part of the Equus beds aquifer, including the Wichita municipal well field, from 1940 to 1980, and (2) simulate the effect that future withdrawal rates could have on the concentration of chloride ion from 1980 to 2020. Sources of the chloride ion were oilfield brine disposed from 1932-43 that is moving toward the well field and water in the Arkansas River. Each simulation projected an increase in the concentration of chloride ion in the Wichita well field. The projections indicated that a continuous 1,000 mg/L source of chloride ion in streamflow losses from the Arkansas River had a greater effect on increasing chloride-ion concentrations in the Wichita well field than did the movement of residual oilfield brine. (Author 's abstract)

Water-Resources Investigations Report↗