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A precision gravity network consisting of approximately 50 stations was established to monitor the Lassen geothermal system. The network was surveyed during the summer of 1982 and tied to a similar network established in 1981. Measurements yielded relative gravity values at the network stations with average uncertainties of 0.007 mGal (1 computed standard error).
Hydration-rind ages based on hydration-rind thicknesses of obsidian and an assumed hydration rate of 5 microns /1000 yrs have been determined for the 26 exposed Mono domes and coulees. Hydration-rind thickness data give good estimates of relative age differences between the domes, but determination of absolute ages will depend upon calibration to radiometric ages. The first extrusion of highly differentiated, sparsely porphyritic rhyolite occurred an estimated 32,000 to 40,000 yrs ago and consists of a small dome at the northwest end of the contiguous chain. The next major extrusive event occurred about 24,000 yrs ago and is represented by two domes and a major tephra. About 10,000 yrs ago the frequency of eruptive activity increases and rhyolite lave was extruded at an average rate of 0.2 km3/1000 yrs; periods of dormancy ranging in length from 300 to 2000 yrs. About 2000 to 3000 yrs ago the rate of extrusion increased dramatically to 0.8 km3/1000 yrs beginning with the eruption of the South Coulee and its associated tephra. At the same time, the nature of erupted magma changed from sparsely porphyritic (3 to 10 per cent sanidine) to aphyric rhyolite. All eruptions since 2000 radiocarbon yrs BP have produced magma that is aphyric but is of the same chemical composition as the earlier porphyritic magma. Volumes of porphyritic and aphyric extrusives, each of which includes volumes of lava and volumes of pumiceous pyroclastics reduced for porosity, are nearly equal and together total about 4 km3. Projecting the recent rate of extrusion over the time since the last major eruption, 1185 radiocarbon yrs ago suggests that a future eruption in the Mono Chain could release as much as 1 km 3 of magma. The recent increase in extrusion rate and the contemporaneous change in the nature of the magma are attributed to an event in the magma chamber that allowed the release of hotter, more fluid, crystal-free magma. The young age for the beginning of rhyolite volcanism from the mono magma chamber suggests that rhyolite magma may have been emplaced in the shallow crust as recently as 32,000 to 40,000 yrs ago. Calculations by Lachenbruch et al. (1976, Jour. Geophys. Research, v. 81, p. 769-784) that a thermal disturbance at this age would have propagated upward by solid conduction only 4 km and offer an explanation for the lack of a heat-flow anomaly and surface indications of hydrothermal activity over the Mono magma chamber and its associated ring-fracture system. This report also contains new information on the age and chemistry of volcanics on the Mono Lake island, the Inyo domes, and tephras within the Long Valley Caldera. A newly discovered rhyolite tuff ring of late Quaternary age in the Toowa volcanic field of the southern Sierra Nevada is briefly described for it represents a new area that should be examined for potential as a geothermal area.
Temperatures within the main vapor-dominated steam reservoir at The Geysers geothermal field generally are in the range 238°C to 244°C. A few deep wells in the northwestern part of the field have penetrated beneath this reservoir into a second vapor-dominated reservoir where temperatures are >315°C, while vapor pressure remains nearly constant at about 35.9 bars (Walters et al., 1992). Vapor-dominated reservoirs generally are thought to operate like heat pipes in which steam formed near the base of the system convects upward (along with other gases, such as CC>2 and H2S), while liquid that has condensed from steam near the top of the reservoir counterflows downward (White et al., 1971). To the extent that this steam condensate carries H2S in solution, it may dissolve gold from the surrounding rock during the counterflow. Re-evaporation of the down-flowing condensate and precipitation of dissolved material might occur at the base of the upper reservoir where there is a relatively sharp increase in temperature while vapor pressure remains nearly constant. In addition, brine that once was present throughout the system (Moore, 1992) may have deposited a variety of ore minerals when and where boiling was vigorous during the transition from previous hot water-dominated to present-day vapor-dominated conditions. The investigation reported here was a geochemical reconnaissance survey looking for evidence of accumulation of Au and other metals in the transition zone between the two reservoirs. The petrology of the cuttings was not examined as part of the investigation.
This report releases the results of selected chemical analyses by the USGS of fluids collected from geothennal power production wells at the Cerro Prieto Geothennal Field, Mexico. Cerro Prieto, the world's largest producing hot-water geothennal field, is located 32 km southeast of Mexicali, Baja California. Comision Federal de Electricidad de Mexico (CFE) gave permission for, and assisted in, sample collection. Data collection and reported analyses was made by the U.S. Geological Survey. Data collected in 1977 and 1978 where published previously by Ball and Jenne (1983) which was about half the data given here. This report also includes samples collected in 1979 which were not previously released. These activities, including this data release, are supported by the U.S. Department of Energy. Analyses given in the following section were made by James W. Ball and E.A. Jenne. The data have been reviewed with the assistance of Cathy Janik, USGS, Menlo Park. Some, but not all, details from Ball and Jenne (1983) concerning collection, and preservation and analytical procedures are repeated here. Nehring and Trusdell (1977) also provide an outline of some of the issues involved in the difficult task of collecting samples from geothermal wells. The initial intent of the study was to provide basic data for use in determining how these fluids should be managed either in disposal or in reinjection. Some of the hot, corrosive brines were separated as two-phase (water and steam) samples under pressure using a coiled condenser tube submerged in an ice/water mixture (called "condensed" samples). It is not known if these were total flow samples. Other samples were collected from the brine sampling valve of the separators (called "flashed" samples). Analyses given in the following section area sorted by (1) well number, (2) date, and (3) sample type(s). Analysis was by a Spectraspan III d.c. argon plasma emission spectrometer with a Spectraject III torch (Ball and Jenne, 1983). Elements were determined in two groups using interchangeable cassettes. Group one included B, Mn, Cu, Zn, Si, Zr, Be, Mn, Sr, Ti, Ca, Fe, Ba, K, Na, Rb, and Al. Group two included As, Se, Bi, Zn, Cd, Sb, Cu, Ni, Hg, Mo, Co, Cr, Fe, V, Tl, Li, and Pb. Ball and Jenne (1983) noted that analysis of B, Ca, Mg, Ba, and Sr generally gave precise results. Movement of the plasma or grating was observed to affect sensitivity over short time periods even while the instrument was carefully standardized and optimized. Sensitivity was also a function of sample concentration. All samples at the time of analysis contained a white precipitate (perhaps colloidal silica) thus the reported concentrations may not accurately represent the concentrations present at the time of collection (Ball and Jenne, 1983). Additional details about specific elements are given in the section on "Evaluation of data" (Bliss, this volume) following the data table.
Hydrothermal mineralogy studies of specimens collected from nine geothermal drill holes suggest that, at the locations and depths drilled, past temperatures have been hottest (exceeding 300?C) near ring fractures on the south and west sides of Newberry Volcano.
Mount Spurr, a 3,374-m-high stratovolcano in the Cook Inlet region of Alaska, showed signs of volcanic unrest beginning in 2004 and lasting through 2006. These signs included increases in heat flow, seismicity, and gas flux, which we interpret as the results of a magmatic intrusion in mid-2004. In response, debris-laden meltwater beneath the glacier in Mount Spurr's geothermally active summit basin accumulated as the overlying snow and ice melted. As heat output increased, the icecap subsided into a growing cavity over a meltwater lake, similar to that observed during subglacial volcanic activity in Iceland. An ice plug collapsed into the lake sometime between June 20 and July 8, 2004, forming an ice cauldron that continued to grow in diameter during 2004 and 2005. A freefall of ice and snow into the lake likely caused a mixture of water and debris to be displaced rapidly upward and outward along preexisting englacial and, possibly, subglacial pathways leading away and downslope from the summit basin. Where these pathways intersected crevasses or other weak points in the sloping icefield, the mixture debouched onto the surface, producing dark, fluid debris flows. In summer 2004, the occurrence of two sets of debris flows separated in time by as long as a week suggests two pulses of summit ice collapse, each producing a surge of water and debris from the lake. A single debris flow was also emplaced on May 2, 2005. This event, which was captured by a Web camera, occurred simultaneously with a lake-level drop of ~15 m. To the east of the ice cauldron, a spillway that fed the debris flows has apparently maintained a relatively constant lake level for months at a time. Aerial photographs show that the spillway is in the direction of a breach in the summit crater. Melting of snow and ice at the summit has continued through 2006, with a total meltwater volume of ~5.4 million m3 as of March 2006.
A reliable determination of the chemical composition of geothermal fluids may require special sampling and preservation techniques. A sample collected without pretreatment is usually adequate for the analysis of sodium, potassium, and chloride. Other constituents may require further treatment or even analysis in the field, depending on the data requirements. The collection and preservation methods described permit accurate results for 31 chemical variables, including major and minor chemical constituents.
As part of a cooperative study with Dr. Alfred Truesdell, water samples collected from geothermal power production wells at Cerro Prieto, Mexico, were analyzed for selected elements by d.c. argon plasma emission spectroscopy. Spectral interferences due to the presence of high concentrations of Ca, Si, Na and K in these water affected the apparent concentration values obtained. These effects were evaluated and correction techniques were developed and applied to the analytical values. Precipitates present in the samples at the time of analysis adversely affected the accuracy, precision and interpretability of the data. (USGS)
Dissolved sulfide (-II) and dissolved iron (II, III) were determined in geothermal well water samples collected at Cerro Prieto, Mexico. Most samples consisted of liquid and gas (two phases) at the instant of collection; and a subset of samples, referred to as ' flashed ' samples, consisted of pressurized steam samples which were allowed to condense. Sulfide was determined by sulfide specific ion electrode; Fe(II) and Fe(III) plus Fe(II) were determined spectrophotometrically. The precision and accuracy of the methods were evaluated for these high-silica waters with replicate analyses, spike recoveries, and an alternate method. Direct current (d.c.) argon plasma emission spectrometry was the alternate method used for Fe(III)-plus-Fe(II) analyses. Mean dissolved iron concentrations ranged from 20.2 to 834 micrograms/L (ug/L) as Fe(II) and 26.8 to 904 ug/L as Fe(III) plus Fe(II). Mean sulfide concentrations ranged from about 0.01 to 5.3 mg/L (S-II) Generally, higher S(-II) values and larger Fe(II)/Fe(III) ratios were found in the two-phase samples. These findings suggest that the ' flashed ' samples are at a less reduced state than the two-phase samples. (Author 's abstract)
This study covers about 1,000 mi 2 (2,600 km 2 ) of the southern Raft River drainage basin in south-central Idaho and northwest Utah. The main area of interest, approximately 200 mi2 (520 km 2 ) of semiarid agricultural and rangeland in the southern Raft River Valley that includes the known Geothermal Resource Area near Bridge, Idaho, was modelled numerically to evaluate the hydrodynamics of the unconfined aquifer. Computed and estimated transmissivity values range from 1,200 feet squared per day (110 meters squared per day) to 73,500 feet squared per day (6,830 meters squared per day). Water budgets, including ground-water recharge and discharge for approximate equilibrium conditions, have been computed by several previous investigators; their estimates of available ground-water recharge range from about 46,000 acre-feet per year (57 cubic hectometers per year) to 100,000 acre-feet per year (123 cubic hectometers per year). Simulation modeling of equilibrium conditions represented by 1952 water levels suggests: (1) recharge to the water-table aquifer is about 63,000 acre-feet per year (77 cubic hectometers per year); (2) a significant volume of ground water is discharged through evapotranspiration by phreatophytes growing on the valley bottomlands; (3) the major source of recharge may be from upward leakage of water from a deeper, confined reservoir; and (4) the aquifer transmissivity probably does not exceed about 12,000 feet squared per day (3,100 meters squared per day). Additional analysis carried out by simulating transient conditions from 1952 to 1965 strongly suggests that aquifer transmissivity does not exceed about 7,700 feet squared per day (700 meters squared per day). The model was calibrated using slightly modified published pumpage data; it satisfactorily reproduced the historic water-level decline over the period 1952-65.
Thermal water 30.0 degrees to 72.0 degrees Celsius is produced from 26 wells and 2 springs in the vicinity of Banbury Hot Springs near Buhl, Idaho. Thermal water is used for residence heating, catfish and tropical fish production, greenhouse operation, swimming pools, and therapeutic baths. In 1979, 10,300 acre-feet of thermal water was utilized; heat discharged convectively from the geothermal system was about 1.1 x 107 calories per second. Decline in artesian head and discharge apparent in recorder charts from two wells may represent seasonal fluctuations or may reflect reservoir response to development of the resource. The thermal waters sampled are sodium carbonate or bicarbonate in character and slightly alkaline. Mixing of hot (72 degrees Celsius) water with local cooler ground water can be shown from various relations among stable isotopes, chloride, and enthalpy. On the basis of concentration of tritium, the age of most of the water sampled is at least 100 years and perhaps more than 1,000 years. Some water (33 degrees Celsius) may be as young as 29 years. On the basis of silica, sodium-potassium-calcium, and sulfate-water geothermometers, the best estimate of the maximum reservoir temperature for the thermal water is between 70 degrees and 100 degrees Celsius.
Present methods are described for the collection, preservation, and chemical analysis of waters produced from geopressured geothermal and petroleum wells. Detailed procedures for collection include precautions and equipment necessary to ensure that the sample is representative of the water produced. Procedures for sample preservation include filtration, acidification, dilution for silica, methyl isobutyl ketone (MIBK) extraction of aluminum, addition of potassium permanganate to preserve mercury, and precipitation of carbonate species as strontium carbonate for stable carbon isotopes and total dissolved carbonate analysis. Characteristics determined at the well site are sulfide, pH, ammonia, and conductivity. Laboratory procedures are given for the analysis of lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, iron, manganese, zinc, lead, aluminum, .and mercury by atomic absorption and flame emission spectroscopy. Chloride is determined by silver nitrate titration and fluoride by ion-specific electrode. Bromide and iodide concentrations are determined by the hypochlorite oxidation method. Sulfate is analyzed by titration using barium chloride with thorin indicator after pretreatment with alumina. Boron and silica are determined colorimetrically by the carmine and molybdate-blue methods, respectively. Aliphatic acid anions (C2 through C5) are determined by gas chromatography after separation and concentration in a chloroform-butanol mixture.
We report 4 years of temperature profiles collected from May 2014 to May 2018 in Integrated Ocean Drilling Program Hole U1364A in the frontal accretionary prism of the Cascadia subduction zone. The temperature data extend to depths of nearly 300 m below seafloor (mbsf), spanning the gas hydrate stability zone at the location and a clear bottom-simulating reflector (BSR) at ∼230 mbsf. When the hole was drilled in 2010, a pressure-monitoring Advanced CORK (ACORK) observatory was installed, sealed at the bottom by a bridge plug and cement below 302 mbsf. In May 2014, a temperature profile was collected by lowering a probe down the hole from the ROV ROPOS. From July 2016 through May 2018, temperature data were collected during a nearly two-year deployment of a 24-thermistor cable installed to 268 m below seafloor (mbsf). The cable and a seismic-tilt instrument package also deployed in 2016 were connected to the Ocean Networks Canada (ONC) NEPTUNE cabled observatory in June of 2017, after which the thermistor temperatures were logged by Ocean Networks Canada at one-minute intervals until failure of the main ethernet switch in the integrated seafloor control unit in May 2018. The thermistor array had been designed with concentrated vertical spacing around the bottom-simulating reflector and two pressure-monitoring screens at 203 and 244 mbsf, with wider thermistor spacing elsewhere to document the geothermal state up to seafloor. The 4 years of data show a generally linear temperature gradient of 0.055°C/m consistent with a heat flux of 61–64 mW/m 2 . The data show no indications of thermal transients. A slight departure from a linear gradient provides an approximate limit of ∼10 −10 m/s for any possible slow upward advection of pore fluids. In-situ temperatures are ∼15.8°C at the BSR position, consistent with methane hydrate stability at that depth and pressure.
Geothermal drill hole CTGH-1, located near Breitenbush Hot Springs in the Cascade Mountains of northwest Oregon, was drilled to a depth of 1463 m. The maximum reported temperature at the bottom of the drill hole was 96.4??C. The drill core consists predominantly of basalt to basaltic andesite lava flows, tuffs, and volcanic breccia. Red to orange iron-oxide stained tuffs are at least partly altered to smectite. Vesicles, fractures, and open spaces between breccia fragments are partly to completely filled by secondary minerals. All of the minerals are compatible with the present low-temperature conditions.
When using a Na-K-???Mg triangular diagram as an aid in the interpretation of a geothermal water, the estimated temperature of last water-rock equilibration may change by as much as 50??C, depending on which of the many Na/K geothermometers one assumes is correct. A particular geothermometer may work well in one place and not in another because of differences in the mineralogy of the phases that are in contact with the reservoir fluid. The position of the full equilibrium line that is used for geothermometry and for assessing degrees of departure from equilibrium also changes as the assumed K/???Mg geothermometer equation changes. The degree of ambiguity can be evaluated by utilizing the results of all the recently published Na/K geothermometers on a single Na-K-???Mg triangular plot.
The Utah Geological Survey complied a preliminary database consisting of over 800 records on thermal wells and springs in Utah with temperatures of 20??C or greater. Each record consists of 35 fields, including location of the well or spring, temperature, depth, flow-rate, and chemical analyses of water samples. Developed for applications on personal computers, the database will be useful for geochemical, statistical, and other geothermal related studies. A preliminary map of thermal wells and springs in Utah, which accompanies the database, could eventually incorporate heat-flow information, bottom-hole temperatures from oil and gas wells, traces of Quaternary faults, and locations of young volcanic centers.
Alid volcanic center, a 700-meter-tall mountain in Eritrea, northeast Africa, straddles the axis of an active crustal-spreading center called the Danakil Depression. Boiling-temperature fumaroles are common on Alid, and their gas compositions indicate a reservoir temperature of at least 250 ??C. The history of volcanism and the high reservoir temperature indicated by the Alid fumarole gases suggest that a geothermal resource of electrical grade lies beneath the mountain. Though drilling is needed to determine subsurface conditions, the process of dome formation and the ongoing crustal spreading can create and maintain fracture permeability in the hydrothermal system that feeds the Alid fumaroles.
Sulfate-water isotope geothermometry for the geothermal system at Twin Falls, Idaho indicates aquifer-temperatures of 90?? to 106 ??C; most sites are between 90?? and 93 ??C. 206Pb/204pb and 280Pb/204Pb of individual thermal waters are principally a function of how much lead has been dissolved from the carbonate and silicate fractions of the Paleozoic limestone collected west of Grand View Peak. Although most thermal waters are recovered from Tertiary rhyolite, very little of the dissolved lead is from the rhyolite. Recharge to this system occurs in northern Nevada and the fluid moves northward in the Paleozoic limestones. The occurrence of thermal fluid in the Idavada Volcanics near and south of Twin Falls, Idaho is the result of upward movement of this fluid from the Paleozoic limestone.