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Geology topics

Donald B. Hoover

Publications and source records attributed to Donald B. Hoover.

At least 37 records · Page 2Linked to original sources
USGS1976

Geology and geophysics of the southern Raft River Valley geothermal area, Idaho, USA

The Raft River valley, near the boundary of the Snake River plain with the Basin and Range province, is a north-trending late Cenozoic downwarp bounded by faults on the west, south, and east. Pleistocene alluvium and Miocene-Pliocene tuffaceous sediments, conglomerate, and felsic volcanic rocks aggregate 2 km in thickness. Large gravity, magnetic, and total field resistivity highs probably indicate a buried igneous mass that is too old to serve as a heat source. Differing seismic velocities relate to known or inferred structures and to a suspected shallow zone of warm water. Resistivity anomalies reflect differences of both composition and degree of alteration of Cenozoic rocks. Resistivity soundings show a 2 to 5 ohm·m unit with a thickness of 1 km beneath a large part of the valley, and the unit may indicate partly hot water and partly clayey sediments. Observed self-potential anomalies are believed to indicate zones where warm water rises toward the surface. Boiling wells at Bridge, Idaho are near the intersection of north-northeast normal faults which have moved as recently as the late (?) Pleistocene, and an east-northeast structure, probably a right-lateral fault. Deep circulation of ground water in this region of relatively high heat flow and upwelling along faults is the probable cause of the thermal anomaly.

Idaho↗
USGS1975

Audio-magnetotelluric methods in reconnaissance geothermal exploration

About three years ago, at the initiation of a major effort by the U.S. Geological Survey into studies of geothermal systems, a decision was made to evaluate the audio-magnetotelluric, AMT, technique for this application. At that time we had had no real experience with the method nor any equipment. Some prior work by Lebel [1971], and Slankis and others [1972], suggested that field operations might be slow and difficult reducing the advantages of the method. A cautious approach was used in developing equipment and field techniques until some experience was gained with the method. As no commercial equipment was available, design and fabrication of the AMT equipment to cover the frequency range 8 Hz to 18,600 Hz was done in-house. Because of the nature of the method, our approach has been to use AMT surveys for reconnaissance exploration and to follow up with other electrical methods in interesting areas. In this paper some of the results of our research are shown to illustrate the effectiveness of the technique.

Open-File Report↗
USGS1974

Geothermal investigations in Idaho, Part 2, An evaluation of thermal water in the Bruneau-Grand View area, southwest Idaho, with a section on a reconnaissance audio-magnetotelluric survey

The Bruneau-Grand View area occupies about 1,100 square miles in southwest Idaho and is on the southern flank of the large depression (possibly a graben) in which lies the western Snake River Plain. The igneous and sedimentary rocks in the area range in age from Late Cretaceous to Holocene. They are transected by a prominent system of northwest-trending faults. For discussion purposes, the aquifers in the area have been separated into two broad units: (1) the volcanic-rock aquifers, and (2) the overlying sedimentary-rock aquifers. The Idavada Volcanics or underlying rock units probably constitute the reservoir that contains thermal water. An audio-magnetotelluric survey indicates that a large conductive zone having apparent resistivities approaching 2 ohm-metres underlies a part of the area at a relatively shallow depth. Chemical analysis of 94 water samples collected in 1973 show that the thermal waters in the area are of a sodium bicarbonate type. Although dissolved-solids concentrations of water ranged from 181 to 1,100 milligrams per litre (mg/l) in the volcanic-rock aquifers, they were generally less than 500 mg/l. Measured chloride concentrations of water in the volcanic-rock aquifers were less than 20 mg/l. Temperatures of water from wells and springs ranged from 9.5 to 83.0 degrees C. Temperatures of water from the volcanic-rock aquifers ranged from 40.0 to 83.0 degrees C, whereas temperatures of water from the sedimentary-rock aquifers seldom exceeded 35 degrees C. Aquifer temperatures at depth, as estimated by silica and sodium-potassium-calcium geochemical thermometers, probably do not exceed 150 degrees C. However, a mixed-water geochemical thermometer indicates that temperatures at depth may exceed 180 degrees C. The gas in water from the volcanic-rock aquifers is composed chiefly of atmospheric oxygen and nitrogen. Methane gas (probably derived from organic material) was also found in some water from the sedimentary-rock aquifers. The thermal waters in the area are believed to be heated by deep circulation in a zone of high geothermal gradient resulting from thinning of the earth?s crust.

Idaho↗