Leveling data across Yellowstone caldera, 1923-1995

This graph shows the rapid uplift (in mm) within the Yellowstone Caldera between 1923 and 1976 (red circles) and 1976 and 1984 (green triangles) followed by several years of subsidence. See simplified map for location of Lake Butte, Mount Washburn, Le Hardy Rapids, and B11.

Scientists suggest the inflation (upward displacement of benchmarks in graph) and deflation (downward displacement of benchmarks) of the Yellowstone caldera are both related to the hydrothermal and magmatic system beneath Yellowstone National Park. Two end-member models can explain most aspects of the historical deformation of the caldera--both involve the cooling and crystallization of magma in the reservoir beneath the park.

In one model, the injection of "new" magma into the reservoir is the primary cause of the uplift. Higher in the reservoir, however, "older" magma crystallizes and releases its gases into the shallow hydrothermal system. The cooling and release of fluids results in subsidence of the ground. If this model is correct, uplift stops and subsidence starts whenever the supply of magma is less than the subsidence rate produced by the crystallization and fluid loss.

In the second model, uplift is caused primarily by pressurization of a very deep hydrothermal system. Gases and fluids released during crystallization of the magma reservoir become trapped beneath an impermeable self-sealed zone. Subsidence occurs during episodic fracturing and injection of fluids into the shallow hydrothermal system.