Geology:
Boiling Springs Lake Thermal Area (BSLTA) is a pristine, high-elevation (1805 m) designated wilderness area of LNVP that includes a large, acidic (pH 2), hot (52C) lake known as Boiling Springs Lake (BSL), several weakly pressurized fumaroles, and small hot springs and mud pots of variable T and pH (Fig. 1). BSL occurs in an area of weakened rock along a fault zone, and is geologically and chemically distinct from caldera-type volcanic lakes typified by the Uzon Caldera and from high chloride, lower sulfate features characteristic of the liquid-dominated geothermal systems in Yellowstone National Park (YNP) (23, 51). BSL is approximately four times the size of the well-known Grand Prismatic Spring in YNP.
The BSLTA has been extensively studied by USGS geologists from the 1980’s to mid-1990’s (49, 58, 81, 89). In 1988, the lake area was measured at ~12 ha, and was estimated to have a maximum lake area of 13 ha (81). At that time, the entire BSLTA covered approximately 14.3 ha. Since the summer of 1999, we have determined approximate lake area, T and pH throughout the summer months (June-August), and these values agreed with previous estimates suggesting this is a relatively stable feature. BSL surface water has an average summer T of ~52C (range 50.5-55C), and an average pH value of 2.0 (1.6-2.3). At the northeast end of the lake is a small outflow stream that is typically dry by early August. The southern end of the lake appears to be the hottest region of BSLTA, where actively bubbling springs and mud pots are continually present, and T ranging from 65-95C, even though many of these features are in direct contact with lake water. On the west and east sides of the lake are a variety of springs ranging in T from 25-93C, pH values from 1- 4.5.
Geochemistry:
Recent (2001) geochemical analyses of BSL water indicate a fairly high SO42- concentration of 833 ppm (~8 mM), and low Cl- concentrations of 0.32 ppm (~9 µM) (75, 77, 78), and these data are similar to those reported for this site in the mid-1980’s (89). Fe, Mn, and Mg are present within BSL water at 688 µM, 4.9 µM, 338 µM, respectively. All other metals (with the exception of Al and Si) were found at fairly low concentrations (data not shown). NH3 is present at only 1.43 ppm (~79 µM) and NO3- is less than 0.02 ppm. Conductivity and total dissolved solids fall within the middle range for other LVNP sites analyzed (3520 S cm-1, and 1071 ppm, respectively). Dissolved organic carbon (DOC) was measured at 1.2 mg/L (summer 2004) (Stedman, unpublished results). Different thermal features within the same thermal region vary widely in chemical composition (51, 75, 78, 89) Gas analyses of features within the BSLTA from the mid-1990’s indicate that mole percent dry weight of the volcanic gases emitted from various sites within the BSLTA are ~88% CO2, 6% N2, 4.7% H2S, 0.28% H2, 0.12% Ar, 0.072% CH4, 0.0015% NH3, 0.008%O2, 0.0007% He, with a gas/steam molar ratio of 0.0024 (51). These gas data vary significantly among different thermal regions within LVNP; however, most sites analyzed within a given region have similar gas compositions.