The geothermal hydrology of Warner Valley, Oregon: A reconnaissance study

Abstract

Supt. of Docs. no.: I 19.2:0r3/5 calorie per cubic centimeter per degree Celsius (cal cm-" 'C-') microsiemens per centimeter (pS cm-I) THE GEOTHERM,QL HYDROLOGY OF WARNER VALLEY, OREGON: A RECONNAIS!SANCE STUDY By EDWARD A. SAMMEL ilnd ROBERT W. CRAIG Warner Valley and its southern extension, Coleman Valley, are two of several high-desert valleys in the Basin and Range province of south-central Oregon that contain thermal waters. At least 20 thermal springs, defined as having temperatures of 20°C or more, issue from Tertiary basaltic flows and tuffs in and near the valleys. Many shallow wells also produce thermal waters. The highest measured temperature is 127"C, reported from a well known as Crump geyser, a t a depth of 200 meters. The hottest spring, located near Crump geyser, has a surface temperature of 78°C. The occurrence of these thermal waters is closely related to faults and fault intersections in the graben and horst structure of the valleys. Chemical analyses show that the thermal waters are of two types: sodium chloride and sodium bicarbonate waters. The warmer waters are likely to have higher concentrations of sodium and chloride, as well as sulfate, silica, and dissolved solids, than the cooler waters. Chemical indicators show that the geothermal system is a hot-water rat,her than a vapor-dominated system. Conductive heat flow in areas of the valley unaffected by hydrothermal convection is probably about 75 milliwatts per square meter. The normal thermal gradient in valley-fill deposits in these areas may be about 40°C per kilometer. Extensive areas underlain by thermal ground water occur near Crump geyser and Fisher Hot Spring. These two areas, located along the western and eastern boundary faults, respectively, are believed to be zones in which hot water, derived from geothermal reservoirs, spreads from the fault zones and mixes with local ground water. Thermal gradients in the valley-fill deposits are extremely high in these areas. Geothermometers and mixing models indicate that temperatures of equilibration are at least 170°C for the thermal components of the hotter waters. The thermal waters probably originate as local meteoric water which circulates to great depths in the fault zones. The depth of circulation may be as great as 4 kilometers, on the basis of the thermal gradients (about 40°C per kilometer) estimated for the valley-fill deposits and bedrock. The size and location of geothermal reservoirs are unknown. If the mixing models are valid, thermal waters of the Crump geyser area and the Fisher Hot Spring area could be derived from a common reservoir. If so, a probable maximum size for such a reservoir is about 38 cubic kilometers a t a depth near 4 kilometers. Total heat stored in the reservoir, above a base temperature of l O T , could be as much as 1.6 x lO"jou1es. A probable minimum value for stored heat, estimated on the basis of the assumption that the thermal fluids a t depth are entirely restricted to the major boundary faults, may be about 5 x lor6 joules. The reservoir a t a de...

Analysis and interpretation of data obtained in tests of the geothermal aquifer at Klamath Falls, Oregon

“…The results are similar in part to those obtained in other fault-controlled geothermal systems in volcanic terrains, such as Warner Valley in south central Oregon (Sammel, 1981) or Newberry Volcano in west central Oregon (Sammel, 1983), where cation geothermometers indicate temperatures significantly lower than original reservoir temperatures. The cation geothermometer and other chemical data at Klamath Falls suggest that the reequilibration zone could represent an extensive and possibly deep low-temperature reservoir.…”

Hydrology of the Newberry Volcano caldera, Oregon

“…However, the large hydraulic gradient between the two sub-basins undoubtedly causes much of the surplus water to flow from east to west across the caldera. Hydrologic studies in other volcanic areas of Oregon indicate that the topographic features of the present caldera floor would not be major obstacles to this near-surface ground-water flow (Sammel, 1980;Sammel and Craig, 1981) Thus the surplus of water from the East Lake sub-basin may be available for ground-water recharge anywhere in the caldera.…”

“…Small flows of ground water were detected in the core hole at depths ranging from 100 to 1,900 feet beneath the caldera floor (Sammel, 1981;and MacLeod and Sammel, 1982).…”

“…The concentration of hydrogen sulfide in gas from this vent also 'is the highest measured in the caldera (R. H. Mariner, USGS, unpublished data 1982). (See, for example, Sammel, 1980;Sammel and Craig, 1981.) Figure 3a shows the relations between chloride and silica in the waters of the caldera.…”

“…The same explanation might account for the possibly anomalous deuterium concentrations in all samples collected by Craig in 1981. A decrease in deuterium of 2 to 4 per mil would place these samples in positions more consistent with the remainder of the isotope data as well as with the chemical analyses. (See, for example Ellis and Mahon, 1977, for a discussion of this phenomenon.)…”