The question of recharge to the geysers and hot springs of Yellowstone National Park

Rye, Robert; Truesdell, Alfred

The extraordinary number, size and unspoiled beauty of the geysers and hot springs of Yellowstone National Park make them a national treasure. The hydrology of these special features and their relation to cold waters of the Yellowstone area are poorly known and in the absence of extensive, deep drillholes are only available indirectly from isotope studies. The 6D - 818O values of precipitation and cold surface and ground water samples fall close to the global meteoric water line (Craig, 1961). 6D values of monthly samples of rain and snow collected over the period 1978 to 1981 at two stations in the Park show strong seasonal variations, with average values for winter months close to those for cold waters near the collection site. 5D values of over 300 samples of cold springs, cold streams, and rivers collected during the fall since 1967 show consistent N-S and E-W patterns throughout and outside of the Park although values at a given site may vary by as much as 8%o from year to year. These data along with hot spring data interpreted earlier (Truesdell et al., 1977; Pearson and Truesdell, 1978), show that recharge to the Yellowstone thermal waters occurs at different levels. Near geyser basins, shallow recharge waters dilute ascending deep thermal waters particularly at basin margins. Deep recharge is heated to >350°C to become the major deep thermal reservoir fluid that supplies steam and hot water to all (?) geyser basins on the western side of the Park. This water (8D = -148 to -150%c) is isotopicafiy lighter than all but the farthest north, highest-elevation, cold springs and streams. The most likely area of recharge for the deep thermal water in the western part of the Park is in the Gallatin Range where major N-S faults connect with the caldera. This recharge area for the deep thermal water is at least 20 kilometers and possibly as much as 70 kilometers from outflow in the thermal areas. Volumetric and flow models based on published chloride flux studies of thermal waters suggests that in a 0.5 to 4 km deep reservoir the residence time of most of the thermal water should be less than 1900 years. The amount of isotopically light water infiltrating in the Gallatin Range during our sampling period may not be enough to provide the present outflow of deep water suggesting that some recharge may have occurred during a slightly cooler time with a greater amount of winter precipitation.

The question of recharge to the geysers and hot springs of Yellowstone National Park

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