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337

GEOTHERMAL SYSTEMS OF

L. J. Patrick Muffler, Charles R. Bacon and W. A. Duffield

Geological Survey, Menlo Park, , USA

Abstract In the central and southern Cascade principal compressive stress. This regional Range, plate convergence is oblique, and stress field influences the formation of Quaternary volcanism produces mostly and fractures and the flow of fluids so that vent mafic ; large andesite- composite alignments and the dikes that fed them have a volcanoes and silicic dome fields occur in north-south preferred orientation (cf. Nakamura, restricted areas of long-lived igneous activity. To the north, plate convergence is normal, producing widely spaced centers in which mafic A growing body of evidence points to the are minor. Most Cascade volcanoes are asthenospheric wedge above zones as short-lived and unlikely to be underlain at the primary source of basaltic for arc shallow levels by large magma bodies that could volcanism. Basalt intrudes the crust at a support high-temperature geothermal systems. distance behind the plate boundary where Such systems are known, however, near Meager horizontal compression owing to plate convergence Mountain, at Newberry , and near Lassen is no longer the dominant component of the stress Peak. Persistent occur on several field. Perhaps none of this magma escapes the major composite volcanoes, but drilling to date crust unmodified, though basaltic has been has been insufficient to determine whether erupted throughout the length of the exploitable geothermal reservoirs occur at the Quaternary. Basalt is seen as the principal depth. Thermal springs away from the major carrier of heat and a significant contributor of volcanic centers are few and generally mass to the more differentiated that are inconspicuous. However, significant geothermal erupted (see Hildreth, 1981). Long-lived igneous systems along and west of the Cascade Range may sytems are evidently compositionally zoned, open well be masked by abundant cold ground water. systems that are repeatedly tapped at the top and resupplied in the roots (Smith, 1979). The Tectonics and volcanism residence time of magma in the crust governs the degree of magmatic differentiation and Quaternary volcanoes of the Cascade Range form a interaction with crustal rocks and fluids, and chain of stratocones, shields, cinder cones, and thus the average composition of magmas that reach domes that lies approximately parallel to the the surface. Pacific coast (figure Tertiary volcanic rocks underlie much of the range (McBirney, From northward, the region where and pre-Tertiary rocks are known to be the direction of plate convergence is roughly present only north of and south of normal to the plate boundary and trend of the . The ends of the Quaternary chain Cascade volcanic chain, volcanic centers are coincide with the onshore projections of the areally restricted and have relatively northern and southern edges of the Juan de Fuca differentiated average compositions. The roughly plate, which is evidently being subducted in a equal spacing of volcanic centers and paucity of northeast direct ion beneath the North American basaltic lava are typical features of volcanism plate (Riddihough, Consequently, the related to ocean-continent convergence. South of ultimate source of magma in the Cascades is Mount Rainier, where plate convergence oblique thought to be related to subduction of the Juan to the plate boundary, the volcanic chain is de Fuca plate. The regional crustal stress broader, vents are less concentrated, and the field, which affects the character of volcanism, Cascade Range contains a higher volume and determined largely by the interaction between proportion of mafic rocks. Presumably this is the much larger North American and Pacific because basaltic magma finds it easier to reach plates. focal mechanisms, north- the surface here where the component of south-trending normal faults, Quaternary dike horizontal compression normal to the volcanic orientations, northwest-southeast-trending chain probably smaller, though there no lateral strike-slip faults within the Cascade reason to believe that the rate of magma Range, and east-west-trending fold axes east of production is everywhere the same. the range indicate that crustal tectonics are dominated by north-south horizontal maximum Large stratocones like (Christiansen 338

Muffler et

0 3

I I Glacier Peak

WASHINGTON I I Rainier I JUAN DE FUCA M Saint I \

I PLATE J

OREGON

Volcano I

PACIFIC PLATE I‘ I - -

dicine Lake Volcano

NEVADA

CALIFORNIA

Figure 1.--Map showing plate-tectonic setting of the Cascade Range. Large arrow indicates direction of convergence of and . Pattern indicates Pliocene and Quaternary volcanic rocks. Triangles indicate major volcanoes. Circles indicate geothermal systems. 339

Muffler et and Miller, 1976) and silicic rocks, as at Crater at Bumpass Hell along the contact between a Lake (Bacon, 1982) and the Lassen field andesitic composite cone and a field (Muffler and others, occur where volcanism of dacite domes that were emplaced during the has taken place for comparatively long periods. past 0.25 The outflow of hot water is Major centers may mark large-scale structural detected at Morgan and Growler Hot Springs in the discontinuities that tend to focus magmatic of Mill Creek 8 to the south of LVNP, activity. Between them, in the region of oblique and at depth in the geothermal well Walker convergence, are smaller stratocones, mafic No. 1 at Terminal Geyser in the southeast corner shields, and cinder cones where magma has not of LVNP. Na-K-Ca, sulfate-water isotope, and been intruded so continuously or resided in the geothermometers indicate that the crust for long. The Simcoe Volcanic Field, deep thermal water feeding Morgan and Growler Hot , , and the Springs has a temperature of 220-240°C (Muffler Caribou Volcanic Field (figure mark areas and others, Temperatures in the Walker where Quaternary volcanism extends to the east of 0 No. 1 well at Terminal Geyser reach a maximum the Cascades crest, merging into the Columbia of 176°C between 603 and 640 m and then decrease Plateau and Basin and Range provinces; these gradually to 124°C in an isothermal zone 18 m centers are here discussed as part of the Cascade thick at the bottom of the hole at 1,222 m Range. Holocene silicic volcanic rocks are (Beall, 1981). Significant contents of K, conspicuous at South Sister, Newberry, Crater and in the fluids produced from Walker Lake, Medicine Lake, Shasta, and . No. 1 (Beall, indicate unequivocally that High-temperature geothermal systems are most the well is drawing upon a hot-water reservoir, likely to be found in such areas, where youthful whereas the reversal in temperature with depth silicic volcanism suggests the presence of indicates that the water flows to the well relatively voluminous and long-lived crustal laterally (presumably from the northwest) rather magma reservoirs (Smith and Shaw, than vertically from below.

Known geothermal systems Most of the Lassen geothermal system is located in LVNP and thus protected from geothermal High-temperature geothermal systems have been development . Walker No. 1 was drilled on identified at three of the major Quaternary private land within LVNP, but title to this land volcanic centers: Meager Mountain (British has subsequently been acquired by the U.S. Columbia), Newberry Volcano (), and Lassen government, and the geothermal energy under that Volcanic National Park (California). In land will not be developed. Morgan and Growler addition, several of the andesite-dacite Hot Springs are on private land, bordered to the composite volcanoes of the Cascade Range display east and west by National Forest land subject to persistent fumaroles and/or hot springs. Among geothermal leasing. However, Federal lease these are Mount (Souther, Mount stipulations require that any geothermal Baker (Frank and others, 1977; Hyde and Crandell, production in this National Forest land will have 1978; Malone, 19791, Mount Rainier and to be carried out without any detrimental effect others, 1963; Crandell and Mullineaux, to the thermal features in LVNP. It remains to Mount Helens (Crandell and Mullineaux, 1978; be seen to what extent this part of the Lassen Lipman and Mullineaux, geothermal system can be developed for commercial (Crandell, 19801, (Crater Lake; use. Williams and Von Herzen, 1982; Bacon, and Mount Shasta (Christiansen and others, 1977; Newberry Volcano Newberry Volcano is a Wharton and Vinyard, With the exception Quaternary volcanic center covering over 1200 of Mount Hood, none of the latter has been at the west end of the High Lava Plains, drilled to any significant depth. Each of these 60 km east of the crest of the Cascade Range volcanoes, however, has had a history of frequent (MacLeod and others, The flanks of the eruption throughout the late Quaternary and has volcano consist of basalt and mafic andesite the potential to support a geothermal system of flows and cinder cones, andesitic to rhyolitic significant size. The climactic eruption of ash-flow and air-fall tuffs, and dacite to Mount Mazama 6,850 yr B.P. produced almost 50 domes; there are over 400 separate vents of silicic magma, and the resulting (MacLeod and others, 1981). At the summit of the attests to the recent presence of a substantial volcano is a composite caldera 6-8 km in diameter magma body in the upper crust. within which are several rhyolitic flows and cones, the youngest of which is only 1,400 Lassen re ion Lassen Volcanic National Park yr old (MacLeod and others, Surface northeastern California, hydrothermal activity is limited to a few warm contains the most conspicuous geothermal .system springs within the caldera 1981). in the Cascade Range. Geological, geochemical, and geophysical observations in the Lassen region Two holes have been on Newberry Volcano all fit a model, originally suggested by D. E. by the U.S. Geological Survey for stratigraphic, White, of a single large geothermal system with a heat flow, and hydrologic information. The first central vapor-dominated reservoir underlain by a was drilled to 386 m at a location approximately zone of hot water discharging at lower elevations 4 km northeast of the caldera to a maximum (Muffler and others, 1982). The focus and major temperature of 9°C (Sammel, 1981). The second thermal upflow of the Lassen geothermal system is well, located just northeast of the 1,400-yr-old 340

Muffler et al. obsidian flow, was drilled 1978 and 1979 to Hood (Hull, and some deeper exploration 631 m; the temperature-depth curve is shown drilling has been carried out at Old Maid Flat the upper part of figure 2. In 1981, this hole (8 northwest of the summit of the volcano) and was deepened to 930 m, and the temperature-depth in the Timberline Lodge area (5 south of the curve shown in the lower part of figure 2 was Well No. 1/2 at Old Maid Flat recorded measured The well was flowed for at 1,220 m (Blackwell and Steele, 20 hours with flow rate declining from whereas well 7A, also at Old Maid Flat, reached 1.5 t o 0.7 after 20 hours. at 1,837 m. However, neither well Chemistry of the reservoir fluid is uncertain, encountered significant permeability. since fluids recovered in the production test appear to be mostly drilling fluid. The USGS has drilled a number of wells for hydrologic testing around Mount Hood. Among The high temperatures at depths greater than these, the Pucci well, just south of the main 700 m the well are masked by the flow of cone, was drilled to 1,220 m, where temperatures cooler ground water at shallow depths (Sammel, of 75-80°C were recorded. One flow test gave as 1981). This situation may be in much of much as 415 L but a subsequent test gave the Cascade Range. In particular, a nearly only 8-10 L probably owing to caving in identical situation may exist at Medicine Lake the hole. Volcano, , a volcanic center whose size, age, geologic evolution, and position Despite the size and youth of Mount Hood, east of the High Cascades are very similar to geothermal exploration to date has been Newberry Volcano. disappointing. High-temperature reservoirs have not been identified, and the low- and Mountain Meager Mountain is located intermediate-temperature found on the the extreme northern part of the Cascade Range, northwest of the volcano is too impermeable to be approximately 190 north of , British exploited. However, most of the 188 of the Columbia, . Meager Mountain a composite volcano has not been drilled and may possibly andesite-rhyodacite dome complex with a volume of contain geothermal resources. about 15 km3 (Read, 1977; Souther, Volcanic activity has migrated progressively to Other geothermal areas Geothermal resources in the north over time during the last 2 with the Cascade Range are not restricted to the major the most recent activity being the eruption of volcanic centers. Substantial resources, silicic pumice from the northern edge of particularly for direct use, occur at lower complex 2,500 years ago (Read, 1979; Souther, elevations on both sides of the Cascade Range. Warm springs occur in the valleys just In Oregon, hot springs appear to be concentrated northeast and just south of the volcanic along a zone separating the the High complex. Cascades from the western Cascades. This fault zone interpreted by (Taylor, to be the Several shallow diamond-drill holes near the warm western margin of a major north-trending graben springs at showed temperatures as 30 km wide filled by Quaternary volcanic rocks of high as at a depth of 600 m (Fairbank and the High Cascades. Deep exploration drilling has others,. 1981). Deep exploration drilling was taken place at Breitenbush Hot Springs along the carried out in 1981-82. The first deep hole had west edge of the graben, but the results are not a temperature of greater than at 2.5 k m , public. whereas the second reached 260°C at 3 km Souther, written communication, 1982). Reservoir Just east of the Cascade Range at Klamath Falls, rocks are fractured granodiorite and metamorphic a reservoir has long been exploited for rocks of pre-Tertiary age. Test data from the heating homes and businesses. Much of the Oregon wells are not yet available, although the first Institute of Technology is heated by geothermal well sustained flashing steam in a 20-cm pipe for fluids, and a district heating system is being 1 hour G. Souther, oral communication, constructed in the central part of the city 1982). A third deep well had reached 3,430 (Lund, 1982). The source of heat for this large August 1982. geothermal system is unknown. The system is located just east of the Cascade range and may Mount Hood Of the Quaternary composite cones therefore be related to igneous activity beneath displaying fumarolic activity, only Mount Hood the range. On the other hand, the geothermal has been subjected to significant drilling. system may be due simply to deep circulation of Mount Hood is a Quaternary andesite-dacite meteoric water along the conspicuous, composite cone that had major eruptive periods at northwest-southeast-trending normal faults that 12,000-15,000 yr B.P., 1,500-1,800 yr B.P., and cut the area. 200-300 yr B.P.; minor air-fall pumice erupted the 1850's and 1860's (Crandell, There Geothermal Potential are fumaroles high on the cone, particularly at Crater Rock, a dacite dome emplaced 200-300 years The Cascade Range has long been recognized as a ago. region of geothermal potential. Brook and others calculated the identified accessible A number of holes have been drilled for heat-flow resource base of geothermal energy in the Cascade and hydrologic purposes on the flanks of Mount Range to be 57 x J. In addition, based 341

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TEMPERATURE,

100 150 200 I I I I I I I I I

I I 400 I I I I I I A 600 A A A A A A A 800 A

MEASUREMENTS ON 6/11/81, PRIOR TO 1981 DRILLING 1000 MEASUREMENTS ON 7/11/81, TWO HOURS AFTER DRILL- ROD PULL

BOTTOM- HOLE TEMPERATURES PRIOR TO DAILY DRILLING

1200 I I I I I I I I I I NO. OR SEPT. 1981

Figure 2.--Composite temperature profile of Newberry 2 drill hole (from Sammel, 1981, Figure 4). 342

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the favorable geologic setting, they production data from the two high-temperature estimated the undiscovered accessible resource systems defined only by drilling (Meager Creek base to be 1,140 x J. If this estimate and Newberry) are not yet sufficient to confirm proves to be correct, the geothermal resources large geothermal reservoirs of high productivity. could a substantial contribution to the Perhaps most of the high-temperature geothermal energy requirements of the . systems at depth beneath the Cascades are small and circulate relatively small volumes of thermal However, despite the high heat flow and the water. Such systems could easily be swamped by presence of Quaternary volcanic rocks throughout overlying cold ground water. This question can the range, geothermal exploration in the Cascade be resolved only after several of these promising Range has not yet been extensive. This low level areas are drilled and their productivity or lack of exploration is due to four main reasons: thereof is demonstrated. 1. The paucity of of thermal manifestations, especially away from the major volcanic References cited centers. 2. The fact that much of the land potentially Bacon, C. R., 1982, Eruptive history of Mount valuable for geothermal resources is Mazama, Cascade Range, U.S.A.: Journal of withdrawn as National Parks or lies in Volcanology and Geothermal Research, in press. National Forests that until recently were Beall, J. J., 1981, A hydrologic model based on not available for leasing. deep test data from the Walker No. 1 3. The abundance and low cost of petroleum in well, Terminal Geyser, California: the , which discourages high- Geothermal Resources Council Transactions, risk exploration ventures in energy sources 5, 153-156. such as geothermal. Blackwell, D. D., and Steele, J. L., 1979, Heat 4. The persistent high interest rates in the flow modeling of the Mount Hood Volcano, United States, which mitigate against Oregon, Hull, D. A., Geothermal resource exploration ventures with only long-term, assessment of Mount Hood: U.S. Department of somewhat uncertain payoff. Energy, Geothermal Energy, The first reason is geologically fundamental and p. 191-264. provides the major challenge for geothermal Brook, C. A., Mariner, R. H., D. R., research in the Cascade Range. Various authors Swanson, J. R., Marianne, and Brook and others, 1979, p. have Muffler, L. J. P., 1979, Hydrothermal suggested that the paucity of thermal springs in convection systems with reservoir the Cascades may be due to masking of temperatures Muffler, L. J. P., hydrothermal convection systems by overlying cold Assessment of geothermal resources of the ground water in the permeable volcanic rocks, United States-1979: U. S. Geol. Survey this effect being enhanced by the high Circular 790, p. 18-85. precipitation throughout much of the region. Christiansen, R. L., Kleinhampl, F. J., Blakely, Indeed, this interpretation is supported by the R. J., Tuchek, E. T., Johnson, L., and results of the Newberry drillhole given above, Conyac, D., 1977, Resource appraisal of where high temperatures were found at depth the Mount Shasta wilderness study area, beneath a zone of circulating cold water County, California: U.S. Geological approximately 700 m thick in an area with only Survey Open-File Report 77-250, 53 weak hydrothermal activity at the surface Christiansen, R. L., and Miller, D., 1976, (Sammel, 1981). The precipitation the Cascade Volcanic evolution of Mount Shasta, Range proper is significantly greater than at California Geological Society of Newberry, and accordingly one would expect a America, Abstracts with Programs, v. 8, stronger masking effect. Masking of high- no. 3, p. 360-361. temperature geothermal systems by overlying cold Crandell, D. R., 1980, Recent eruptive history of water is also compatible with the data from Mount Hood, Oregon, and potential hazards Meager Creek, where a geothermal system of from future eruptions: S. Geological at depth is expressed at the surface Survey Bulletin 1492, 81 only by springs of (Souther, On Crandell, D. R., and Mullineaux, R., 1967, the other hand, there are many volcanic belts Volcanic hazards at Mount Rainier, throughout the world where precipitation is high : U.S. Geological Survey Bulletin and yet there are very significant geothermal 26 systems expressed at the surface Japan, Crandell, D. R., and Mullineaux, D. R., 1978, the Philippines, New Zealand). Furthermore, the Potential hazards from future eruptions of geothermal system at Lassen Peak, an area of very Mount Helens volcano, Washington: U.S. heavy snowfall, finds conspicuous surface Geological Survey Bulletin 1383-C, 26 expression. Fairbank, B. D. Openshaw, R. E., Souther J. G., and Stauder, J. J., 1981, Meager Creek In summary, the available data suggest that high- geothermal project--an exploration case temperature geothermal reservoirs may be history: Geothermal Resources Council associated with major volcanic centers of the Bulletin, v. 10, No. 6 , Cascade Range. With the exception of the Lassen system, however, the surface expression of these systems is weak. Furthermore, available 343

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Fiske, R. S., C. A., and Waters, A. C., Read, P. B., 1979, Geology, Meager Creek 1963, Geology of Mount Rainier National Park, geothermal area, British Columbia: Washington: U.S. Geological Survey Geological Survey of Canada Open File 603 Professional Paper 444, Frank, David, M. F., and Swanson, D. A., Riddihough, R. P., 1978, The Juan de Fuca plate: 1977, Assessment of increased thermal American Union Transactions, activity at , Washington: U.S. Geological Survey Professional Paper 1022-A, Sammel, E. A., 1981, Results of test drilling at Newberry Volcano, Oregon--and some Hildreth, Wes, 1981, Gradients silicic magma implications for geothermal prospects the chambers: Implications for lithospheric Cascades: Geothermal Resources Council magmatism: Journal of Geophysical Research, Bulletin, v. 10, No. 11, 3-8. 86, 10153-10192. Smith, R. L., 1979, Ash-flow magmatism, Hull, D. A., 1979, Geothermal resource assessment C. E., and W. E., Ash-Flow of Mount Hood: U.S. Department of Energy, Tuffs: Geological Society of America Special Geothermal Energy, Final Report Paper 180, p. 5-27. 330 Smith, R. L., and Shaw, H. R., 1975, Hyde, J. H., and Crandell, D. R., 1978, related geothermal systems: in White, D. E., Postglacial volcanic deposits at Mount Baker, and Williams, D. L. of Washington, and potential hazards from future geothermal resources of the United States eruptions: U.S. Geological Survey --1975: S. Geological Survey Circular Professional Paper 1022-C, p. 726, 58-83. Lipman, P. W., and Mullineaux, D. R., eds., 1982, Souther, J. G., 1980, Geothermal reconnaissance The 1980 eruptions of Mount Helens, in the central Garibaldi belt, British Washington: U.S. Geological Survey Columbia: Geological Survey of Canada Paper Professional Paper 1250, 844 p. p. 1-11. Lund, J. W., 1982, Current status of geothermal Souther, G., 1981, Canadian geothermal utilization in Klamath Falls, Oregon: research program, Halbouty, M. T., ed., Proceedings of the International Conference Energy Resources of the Pacific Region: on Geothermal Energy, Florence, Italy, p. American Association of Petroleum , 121-130 (Published by BHRA Fluid Engineering, Studies in Geology, no. 12, p. 391-400. Bedford, ). Taylor, E. M., 1981, Central High Cascade MacLeod, N. Sherrod, D. R., Chitwood, L. A., roadside geology, Bend, Sisters, McKenzie and McKee, E. H., 1981. Newberry Volcano, Pass, and Santiam Pass, Oregon, Johnston, Oregon, Johnston, D. A., and D. A., and Donnelly-Nolan, Julie, eds., Donnelly-Nolan, Julie, Guides to some Guides to some Volcanic in volcanic terranes in Washington, Idaho, Washington, Idaho, Oregon, and Northern Oregon, and Northern California: U.S. California: U.S. Geological Survey Circular Geological Survey Circular 838, p. 85-91. 838, 55-58. MacLeod, N. Walker, G. W., and McKee, E. H., Wharton, R. A., and Vinyard, W. C., 1979, Summit 1976, Geothermal significance of eastward thermal springs, Mount Shasta, California: increase in age of upper Cenozoic rhyolitic California Geology, February 1979, p. 38-42. domes in southeast Oregon: Second United Williams, D. L., and Von Herzen, R. P., 1982, On Nations Symposium on the Development and Use the terrestrial heat flow and physical of Geothermal Resources, San Francisco, May limnology of Crater Lake, Oregon: Journal of 1975, 1, 465-474. Geophysical Research, v. 87, press. Malone, S. D., 1979, Gravity changes accompanying increased heat emission at Mount Baker, Washington: Journal of Volcanology and Geothermal Research, v. 6 , no. p. 241-256. McBirney, A. M., 1978, Volcanic evolution of the Cascade Range: Annual Reviews of Earth and Planetary Science, v. 6, p. 437-456. Muffler, L. J. P., Nehring, N. L., Truesdell, A. Thompson, J. M., Clynne, M. A., and Janik, C. J., 1982, The Lassen geothermal system: Pacific Geothermal Conference, Auckland, N. Z. press). Nakamura, 1977, Volcanoes as possible indicators of tectonic stress orientation: Journal of Volcanology and Geothermal Research, v. 2, p. 1-16. Read, P. B., 1977, Meager Creek volcanic complex, southwestern British Columbia: Geological Survey of Canada Paper p.