Water level records used to evaluate deformation within the Yellowstone caldera, Yellowstone National Park

Abstract

Water level records from gages on the shore of Yellowstone Lake and at its outlet are used to evaluate deformation year-by-year since 1923 on the southeastern flank of Yellowstone caldera. There is good agreement with deformation as measured by precise benchmark leveling surveys in 1923, 1976, 1983, 1984 and 1985. The water level record provides documentation of historical deformation of a large, dynamic, silicic caldera available by no other means, and it gives detail lacking from benchmark leveling prior to 1983 when annual surveys began. The data from southwest of Fishing Bridge suggest that this portion of the caldera has undergone relatively monotonic inflation since 1923 (0.4 μ radian/a up to the northeast) with a small, quasi-oscillatory variation superimposed. North of Fishing Bridge, the data suggest a higher rate with onset of quasi-oscillatory uplift ca. 1940 and a leveling-off since ca. 1965. Of particular importance are: the suggestion of episodic uplift and subsidence; the apparent lack of significant devation at the time of the M = 7.5 Hebgen Lake earthquake (1959); and the apparent subsidence of the intra-caldera area north of Fishing Bridge at the time of the M = 6.1. Norris earthquake (1975) with concurrent inflation of the flank of the caldera to the southwest.