Michael A. Korosec, William M. Phillips, and J. Eric Schuster
With contributions from
Z.F Danes, J.H. Biggane, P.E. Harnmond, and G.A. Clayton
Washington State Department of Natural Resources
Division of geology and Earth Resources
Open File Report 83-7
Under U.S. Department of Energy Contract
Page 3 – 6 of the Report
Scenic Hot Springs
T.26 N, R.13 E, SE1/4 Sec. 28
Scenic (1965) 7.5’ USGS Quad
The Scenic area is reached by taking U.S. Route 2, which follows the South Fork Skykomish River and crosses Stevens Pass. About 8 road km west of Stevens Pass, a few buildings mark the site of the abandoned town of Scenic. Two kilometers to the east, near the wets portal of the Burlington Northern cascade Tunnel, a power line access road traverses upslope to the south. An area of hot springs is reached by following the access road up to the power lines, continuing east along the maintenance road, and by taking the foot path which climbs a few hundred meters further upslope, in a southwesterly direction.
At least four distinct areas of hot springs occur on the moderately steep slope above the Skykomish River. Although totally surrounded by U.S. Forest Service land, part of the Snoqualmie National Forest, the main spring area is a private inholding. The four spring areas are aligned northeast-southwest, with the hottest, and most elevated springs on the southwest end and the coolest, lower springs to the northeast.
|Area 1||SEA||39.2 - 46.5C||160|
|SEB||42.4 – 44.5||195|
|Area 2||SEC||14 – 36.5||140|
|Area 3||SED||31.0 – 32.7||160|
|Area 4||-----||15.0 – 27.0||----|
The temperature ranges listed in the table above are due to two factors. They represent variations observed from spring to spring within the area, and substantial seasonal variations observed over only a portion of the year, in 1981. A more detailed description of each area follows.
The main spring of the area to the southwest (highest in elevation, this is the source for the Lobster Pot) flows from a joint in exposed granitic bedrock into a plastic-lined wooden tub. The water has a slight H2S odor, and a small amount of white filamentous bacteria clings to the side of the channel and tub. Temperature and flow changed from late June to late September. Temperature increased from 39.2 to 46.5oC, while flow decreased by roughly 1/3 (estimated at 40 to 50 l/m, down to 25 to 35 l/m). Samples SEA-1 and SEA-2 were collected from this spring.
About 10 meters west of the tub, a small spring issues from under dense brush, at about the same elevation as the tub ( The source for the Bear Pool). This spring, with a flow of only about 15 to 20 l/m, had the highest temperature of all the Scenic Springs in the early summer, at 42.4oC. By late summer it temperature had increased, but was less than the main spring, reaching only 44.5oC. this suggests that this spring is less influenced by mixing with the seasonally affected ground waters.
A second thermal area (Meadows), downslope to the northeast of the first, includes numerous small springs and seeps which issue from a muddy water-saturated slope in a broad, shallow drainage. A small pool had been dug and lined with plastic to catch water from some of the warmest springs. Most of the temperatures ranged from 14o to 30oC, but a maximum of 36.5oC was measured near the bottom of the plastic lined pool. In early summer, the total flow from this area was estimated to be 150 to 200 l/m. Many of the springs and seeps had dried up by late summer, but the warmest springs continued to flow, with somewhat high temperatures, being less influenced by surface and shallow ground waters.
The third thermal area (Honeymoon), downhill and northeast of the second area, consists of a single large spring which feeds a shallow rock-dammed pool. The flow was about 100 to 180 l/m, with a temperature of 31.0oC, increasing to 32.7oC by late summer.
The fourth thermal area is located within the power line corridor, and has obviously been disturbed by construction of the corridor. Numerous warm springs issue from alluvium in a poorly defined drainage, forming a marshy area. Temperatures are much cooler than springs in other area, ranging up to 27oC, there is a possibility that the water in this area originates from warmer springs upslope, flows downslope through alluvium, and emerges where the alluvium has been disturbed.
I am in general agreement that this fourth thermal area is essentially seepage through the grouse alluvium, rather than actual springs, themselves. We have recently discovered several more springs lower down with good temperature and flow potential. These may be nothing more than seepage as well. There are a few more sites that need to be evaluated vis a' vis springs or seepage.
Considering the relatively warm temperatures, the Scenic springs have a very low salinity. The waters are weak sodium bicarbonate, with high sulfate relative to the concentrations of the other anions. The lithium, potassium, and magnesium concentrations are very low, and the silica is relatively low.
Geothermometers applied to water samples from various springs at Scenic give the following results:
The Scenic Hot Springs issue from granodiorite and quartz diorite, part of the Mount Stuart batholith (Pratt, 1958). Potassium-argon age dates range from 80 to 90 million years before present, with an average of 88 m.y. (Engels and Crowder, 1971). No structural features have been described in the literature for the immediate area of the springs, but the northeast-southwest alignment of the spring groups, roughly paralleling the Skykomish River valley to the north-northwest, suggest possible fault or joint control of the springs.
Two heat flow holes were drilled in the vicinity of the Scenic Hot Springs during the summer of 1981, Scenic No. 1 (T. 26 N., R. 13., SE1/4 of SW1/4 of Section 28), completed to 101.5 meters, was drilled less than ½ km north of the hot springs, downslope about 200 meters in elevation. It produced a gradient of 48oC/km in the upper one half, and 68oC/km in the lower portion of the hole. These are very high gradients for granodiorite, and are probably due to the proximity to the hot springs. Using a gradient of 68oC.km and a thermal conductivity of 2.06 W/m.K, the heat flow (not corrected for topography) would be 140mW.m2. A correction for topographic effects lowers the heat flow to 115 mW/m2. (This wellhead is located at the bottom of the loop road prior to the steep drive up the BPA access road)
Scenic No. 2 (T. 26 N., R. 13 E., NE1/4 of NW1/4 of Section 27), was drilled about 2 km to the east-northwest of No. 1. It was completed to 152 meters and penetrated biotite schist, probably part of the Carboniferous Chiwaukum Schist. The gradient is 36.5oC/km, and using a thermal conductivity of 2.68 W/m.K, the heat flow is calculated to be 98 mW/m2. A topographic effect correction lowers the heat flow value to 70 mW/m2. These heat flows are much higher than had been expected for the Central Cascades of Washington.We are still looking for this wellhead)
The good agreement between different geothermometers and the relatively consistent results for different spring groups suggest that the thermal waters are in equilibrium with reservoir rocks at about 90 to 105oC. The very low concentrations of salts, however, and the observed seasonal variations, imply significant mixing.