Abrupt physical and chemical changes during 1992-1999, Anderson Springs, SE Geyser Geothermal Field, California
<p>The Anderson Springs area is located about 90 miles (145 kilometers) north of San Francisco, California, in the southwestern part of Lake County. The area…
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Anderson Springs (AS), located in the southwestern part of Lake County, CA, was first developed in the late 1800s as a health resort, which was active until the 1930s. Cinnabar was extracted from a few small mines (e.g. Big Chief, Thorne) in the bluffs south of the resort area, mostly from the 1870s to the 1940s. About 1260 flasks of Hg were produced from these mines. By the early 1970s, the higher ridges west and south of AS became part of the southeast sector of the greater Geysers geothermal field. Today, several electric power plants are built on these ridges, producing energy from a vapor-dominated 240°C reservoir. Only the main hot spring at AS has maintained a recognizable identity since the 1930s. The hot spring is actually a cluster of seeps and springs (total discharge L/min) that issue from a small fault cutting Franciscan metagraywacke in a ravine SW of Anderson Creek (AC). Published and unpublished records show that the maximum temperature (Tm) of this cluster fell gradually from 63°C in 1889 to 48°C in 1992. However, Tm of the cluster climbed to 77°C in 1995 and neared boiling (98°C) in 1998. A new cluster of boiling vents and small fumaroles formed in 1998 (Tm 99.3°C), about 30 m north of the old spring cluster. In 8/99 the new hot spring cluster was about 25 m in length and had a total discharge of about 0.5 L/min. Several evergreen trees on steep slopes immediately west of these vents apparently were killed by the new activity. Tm of the old spring cluster decreased to 78°C by 8/99, but measured 85°C in 9/99. Thermal waters at AS are largely suface waters with added condensed steam and gases from the subjacent geothermal reservoir. The volume of steam condensate is very small compared to the volume of meteoric water. Compared to gas samples from Southeast Geysers wells, AS gases are higher in CO2 and lower in H2S and NH3. The hot spring waters are low in ions of Cl and B, but are relatively high in HCO3, SO4 and NH4. The waters have stable-isotope compositions that plot near the global meteoric water line, and contain a small amount of anthropogenic tritium (4.6 TU in 1991; 2.5 TU in 1999; pre-bomb background 3 TU). Geochemical data through time reveal few consistent changes, but there were apparent maxima in the concentrations of SO4, Ca, Fe, and Mn in 1991 to 1992, before the cluster became hotter. The black-to-gray deposits from the new spring cluster are rich in pyrite and contain anomalous metals. Fine silt and colloids filtered from a water sample in 1998 contained high metal concentrations. As early as 1988, about 1/2 mile east of the main hot spring, an old mine adit (Schwartz Mine) in a drainage south of AC began to discharge mineralized water intermittently. In 7/98, a sudden discharge of gray, silty water flowed into AC. In 12/98, Tm of the adit water was 22°C. Flow from the adit reportedly stopped during early summer of 1999 but resumed in 8/99 (10 L/min). Compositionally, the adit water is similar to waters at AS hot spring and resembles tepid spring waters (17 to 23°C) that once discharged in the ravines surrounding the former AS resort. ABSTRACT Abrupt Physical and Chemical Changes During 1992-1999, y r o t a r o b a a n o t a N s o m a A s o E a r t h & E n r o n m e n t a S e n e Cathy J. Janik Stephen R. Walter Fraser Goff Michael L. Sorey Dale Counce Photo looking SE of power plant (Unit 16), SE Geyers geothermal field. Big Chief Mine Unit 16 Power Plant Thorne Mine Fumarole (weak) Unnamed Adit Hot Springs Bear Canyon Creek Anderson Gunning Creek Rd. Socrates Mine Wardlow Rock Castle Rock Hot Spg (dry) Anderson Springs SE GEYSERS Topographic map of Anderson Springs area; contours in feet. 1 Main Hot Spring 2 New Hot Spring 3 Fe-rich Spring 4 Tributary/Hot Spring Drainage 5 Schwartz Mine Water 6 Schwartz Drainage Schwartz Mine San Fransisco The Geysers N 2000 ft 600 m Creek Anderson Hot Springs/Drainage (values in ppm) Map Site Date Temp. pH SiO2 Ca Mg Fe Mn Hg NH4 HCO3 SO4 Cl B No. (°C) (lab) 1 Main Spg 9/98 68 7.13 73 76 32 0.70 4.83 0.0002 20.0 332 228 2.0 0.45 1 Main Spg 12/98 50 6.94 51 52 23 0.96 4.33 <0.0001 11.1 224 150 2.8 0.33 1 Main Spg 8/99 70 7.13 75 72 29 0.38 3.83 <0.00005 23.2 348 206 2.0 0.52 2 New Spg 9/98 90 7.58 66 30 11 0.18 0.82 0.0009 28.5 101 165 1.8 0.43 2 New Spg 8/99 98 8.36 75 17 3.9 0.02 0.29 0.00055 24.9 37 179 1.5 0.52 3 Fe-rich Spg 8/99 21 6.27 39 83 51 1.41 3.54 <0.00005 0.54 32 445 2.1 0.05 4 Drainage 8/99 21 5.90 41 40 25 7.12 1.78 <0.00005 2.13 0.8 261 2.4 0.21 -- Cold Spgsa 12 6.4 40 5 3 ≤0.2 ≤0.2 39 1 4.2 ≤0.15 aAverage of four analyses from Thompson et al. (1981). The thermal waters display some chemical similarities (e.g., high NH4 and SO4 but low Cl).
They are different from typical cold spring waters in the area. See Janik et al. (1999) for complete analytical data. Gas Analyses, Anderson Hot Springs (mol-% dry gas) Map Site Date Temp CO2 H2S H2 CH4 NH3 N2 O2 Ar D-Pa No. (°C) (°C) 1 Main Spg 3/91 49.4 82.1 0.35 0.14 5.19 n.a. 10.1 1.76 0.12 218 1 Main Spg 3/95 76.6 90.5 2.91 0.03 3.85 0.0018 2.55 n.d. 0.04 229 2 New 8/99 98.4 64.5 4.85 5.50 1.15 0.29 22.5 0.78 0.31 230 -- SE Geysers Wellsc 49.0 12.3 22.3 5.14 6.19 4.66 <0.01 0.06 aGas geothermometer of D'Amore and Panichi (1980). bAlso contains 0.00043 mol-% Hg. cMean composition of 27 gas analyses for the SE Geysers from Lowenstern et al. (1999). Metals, Muck & Residue, New Hot Spring (Sept., 1998; values in ppm) As Cu Hg Pb Sb Se Tl Zn S Fe2O3 (wt-%) Muck 14 45 30 12 23 0.51 0.79 80 21000 9.2 Residuea 90 350 520 470 400 23 350 19.9 aFiltered from 400 ml of spring water. Schwartz Mine Adit and Drainage (values in ppm) Map Site Date Temp. pH SiO2 Ca Mg Fe Mn Hg NH4 HCO3 SO4 Cl B No. (°C) (lab) 5 Adit 12/98 22 6.15 69 108 54 8.2 4.8 <0.0001 10.2 62 508 1.9 0.09 5 Adit 8/99 19 6.67 69 128 60 6.5 4.5 <0.00005 14.1 175 520 1.6 0.10 6 Drainage 8/99 12 6.54 44 92 45 0.02 2.9 <0.00005 0.8 7.4 443 1.7 0.16 -- "Sulphur" 1889 17 42 185 117 3.9 --- 455 413 11 --- -- "Belmer" 1889 23 72 132 43 1.0 --- 175 617 6.7 tr -- "Sour" 1889 18 68 10 17 6.7 1.1 0.7 220 0.8 tr Orange precipitates of Fe-Mn hydroxides, silica and Ca-Mg carbonates and sulfates form as water flows from the adit down the natural drainage, consistent with the chemical data. Adit water is chemically similar to water from the Fe-rich Spring (see map site 3), and most closely resembles water from Belmer Spring which was used at the Anderson Springs resort until Date Maximum Temp (°C) Ca Fe Mn SO4 HCO3 Time variations of temperature and selected chemical components (ppm) at Anderson Hot Springs. Temperature decreased slowly from 62 to 48°C and then rose quickly to 98°C. There are apparent maxima in Ca, Fe, Mn, and SO4 in the early 1990s. Other components such as HCO3 show no clear trends. Photo of gas sampling at New Hot Spring. U.S. Department of the Interior U.S. Geological Survey Open-File Report 00-037, Version 1.0 Sheet 1 Elizabeth M. Colvard U.S. Geological Survey 345 Middlefield Road Menlo Park, CA 94025 2Los Alamos National Laboratory EES-1 Geology/Geochemistry Los Alamos, NM 87545 Muck at the New Hot Spring (site 2) consists of black to gray silty to colloidal solids (see photo of gas sampling), rich in pyrite and Fe-oxides. The muck is somewhat anomalous in metals, and the filter residue collected during water sampling is especially rich in metals. As the hot spring area increased in temperature, there was a sympathetic increase in H2S, H2 and NH3, and a decrease in CO2 and CH4, becoming more like the mean composition of steam discharges from the SE Geysers. the 1930s.
Anderson Springs, SE Geysers Geothermal Field, California Photo of dead trees west of New Hot Spring area. Waters at Anderson Springs are meteoric in character. They do not have enriched isotope values like most other regional thermal waters, which are mixtures of meteoric and connate fluids. +4 +2 Most Regional Cold Meteoric Water Mean SE Geysers Steam δD (0/00) δ18O (0/00) Anderson Springs Main Spring New Spring Schwartz Mine Water Regional Mixing Trend with Connate Water SMOW CONCLUSIONS The cause for the abrupt physical and chemical changes that have occurred in AS waters since 1992 is still not resolved. One obvious possibility is that 20+ years of steam withdrawal from the geothermal reservoir has caused pressure declines that have induced boiling in the condensation zone. This would cause heating and vaporization of shallow ground waters in the vicinity of AS. In addition, earthquakes in this seismically active region may have enhanced surface discharge of these thermal fluids along fractures and faults. Anderson, W., 1892, Mineral springs and health resorts of California: Bancroft, San Francisco, 384 p. Beall, J.J., Stark, M.A., Smith, J.L.B., and Kirkpatrick, A., 1999, Microearthquakes in the Southeast Geysers before and after SEGEP injection: Geothermal Resources Council Trans., 23, 253-257. Berkstresser, C.F., 1968, Data for springs in the northern Coast Ranges and Klamath Mountains of California: U.S. Geological Survey Water Resources Division Open-File Report., 49 p. Donnelly-Nolan, J.M., Burns, M.G., Goff, F., Peters, E.K., and Thompson, J.M., 1993, The Geysers-Clear Lake area, California: Thermal waters, mineralization, volcanism, and geothermal potential: Econ. Geology, 88, 301-316. Eberhart-Phillips, D., and Oppenheimer, D.H., 1984, Induced seismicity in The Geysers geothermal area, California: J. Geophys. Res., 89, 1191-1207. Goff, F., and Janik, C.J., 1993, Gas geochemistry and guide for geothermal features in the Clear Lake region, California, in Rytuba, ed., Active Geothermal Systems and Gold-Mercury Deposits in the Sonoma-Clear Lake Volcanic Fields, California: Society of Economic Geology Guidebook 16, 207-261. Goff, F., Adams, A., Trujillo, P., Counce, D., and Mansfield, J., 1993, Geochemistry of Thermal/Mineral Waters in the Clear Lake Region, California, and Implications for Hot Dry Rock Geothermal Development: Los Alamos Nat'l. Lab. Rept. LA-12510-HDR, 23 p. Goff, F., Donnelly, J.M., Thompson, J.M., and Hearn, B.C., 1977, Geothermal prospecting in The Geysers-Clear Lake area, northern California: Geology, 5, 509-515. Ingebritsen, S.E., and Sorey, M.L., 1988, Vapor-dominated zones within hydrothermal systems: Evolution and natural state: J. Geophys. Res. 93, 13,635- 13,655. Janik, C.J., Goff, F., Sorey, M.L., Rytuba, J.J., Counce, D., Colvard, E.M., Huebner, M., White, L.D., and Foster, A., 1999, Physical, chemical, and isotopic data for samples from the Anderson Springs, Area, Lake County, California, 1998-1999: U.S. Geological Survey Open-File Report 99-585, 27 p. Lowenstern, J.B., Janik, C.J., Fahlquist, L.S., and Johnson, L.S., 1999, Gas and isotope geochemistry of 81 steam samples from wells in The Geysers geothermal field, Sonoma and Lake Counties, Calif., USA: U.S. Geological Survey, Open-File Report 99-304, 28p. McLaughlin, R.J., 1978, Preliminary geologic map and structural sections of the central Mayacmas Mountains and The Geysers steam field, Sonoma, Lake and Mendocino Counties, California: U.S. Geological Survey Open-File Map 78-389, Scale 1:24,000. Oppenheimer, D.H., 1986, Extensional tectonics at The Geysers geothermal area, California: J. Geophys. Res., 91, 11463-11476. Thompson, J.M., Goff, F.E. and Donnelly-Nolan, J.M., 1981, Chemical analyses of waters from springs and wells in the Clear Lake volcanic area, in R.J. McLaughlin and J. M. Donnelly-Nolan (eds.) Research in The Geysers- Clear Lake Geothermal Area, Northern California: U.S. Geological Survey Professional Paper 1141, 183-191. Waring, G.A., 1915, Springs of California: U.S. Geological Survey, Water-Supply Paper 338, 440 p. White, D.E., Muffler, L.J.P., and Truesdell, A.H., 1971, Vapor-dominated hydrothermal systems compared with hot-water systems: Econ. Geology, 66, 75-97. Fault Plant Condensation Zone Vapor Zone Anderson Hot Springs SE Geysers Steam Wells S N Anderson Creek Schematic diagram (not to scale) showing possible cause of increased temperatures at Anderson Hot Springs. As steam in the reservoir is depleted, water in the condensation zone "dries out" and the condensation zone shrinks. Deep steam has a more direct pathway to the surface and shallow ground waters are heated, especially along faults. dead trees Anderson Main Hot Spring 68°C 79.3°C 74.1°C 84.9°C 83.6°C, pale yellow New Hot Spring 99.5°C To Anderson Creek Road/trail Iron-stained tributary Old cinder-block structures red oozing seep 61.4°C Runoff channel Ground temperature measurement at 5 cm depth (°C) Spring Excavated area N 10 meters 20 feet Schematic diagram of the Anderson Hot Springs showing measured temperatures (9/16/99) of the springs and the ground in the vicinity of the springs. Shaded area on the west bank of the spring-discharge channel indicates the approximate size of the dead-tree zone. The ambient air temperature for the region is approximately 13°C (Goff et al., 1977). dead trees Anderson Main Hot Spring 68°C 79.3°C 74.1°C 84.9°C 83.6°C, pale yellow New Hot Spring 99.5°C To Anderson Creek Road/trail Iron-stained tributary Old cinder-block structures red oozing seep 61.4°C Runoff channel Excavated area CO flow measurement g d-1m-2 Spring N 10 meters 20 feet Schematic diagram of the Anderson Hot Springs showing diffuse flow of CO2 through soil in the vicinity of the hot springs. CO2 flow measurements were made on 9/16/99 near each site where ground temperatures were measured. These CO2 fluxes are considered to be too low to kill the trees. The most likely cause of tree kill is heat stress in the root zone. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ACKNOWLEDGEMENTS: This work was funded by a grant from the U.S. Department of Energy, Office of Geothermal Technologies, as well as the USGS Volcano and Earthquake Hazards Programs. We thank Anthony Garcia (LANL) and Jake Lowenstern (USGS) for assistance with drafting and publication. Seismic activity is correlated with the geothermal system at The Geysers. Earthquakes occuring within 3 km of Anderson Springs increased significantly after 1980 as nearby powerplants began operation. Seismicity indicates that failure occurs on small faults or fractures in regions of geothermal production and injection. Historical faults Holocene faults Quaternary faults FAULTS le ar Lake Clearlake Lower Lake Middletown Anderson Springs Cobb Kelseyville Earthquake hypocenters from 19901999 displayed along cross section A-A' from map at lower left. Events ±3km perpendicular to the section line are projected on to the plane A-A'. Symbol sizes and colors are the same as in the seismic map. Earthquake depths
referenced to mean station elevation shown by dashed red line. Nearly all events are deep, indicating the presumed vertical extent of the geothermal system. Vertical error ±0.4 km. Horizontal error ±0.1 km. U.S. Department of the Interior U.S. Geological Survey Open-File Report 00-037, Version 1.0 Sheet 2 y r o t a r o b a a n o t a N s o m a A s o E a r t h & E n r o n m e n t a S e n e S A Southeast Geysers Southeast Geysers Useful References Global Meteoric Water Line m m Fault traces were digitized from Jennings (1994: California Division of Mines and Geology State Fault Map, Scale 1:750,000) and are accurate herein to 0.8 km. Brown dashed box displays limit for hypocenters projected in cross section at above right. This poster is available on the World Wide Web at ://geopubs.wr.usgs.gov/open-file/0f00-037/