Abstract

The 1959 Hebgen Lake earthquake triggered increased interest in the geology of Yellowstone and the surrounding area, especially the relationship between seismic and hydrothermal activity. By the mid-1960's this work had moved beyond its original scope, as it became known that the area was blanketed by ash-flow tuffs, with the recognition of major volcanic calderas. In the mid-to-late 1960's, the U.S. Geological Survey became heavily involved, with NASA support, in a variety of investigations, including studies of Eocene and Quaternary volcanics, glacial and surficial geology, and hydrothermal geology and geochemistry. The major products of this period of field work included fullpark bedrock and surficial geological maps, revised mapping on most 15 minute quadrangles of the park, and many technical papers. Some are still forthcoming.

The accomplishments of the U.S. Geological Survey set the stage for and attracted the interest of other earth scientists who are now focusing upon some of the larger questions of the volcanic history of Yellowstone, its setting in the tectonic framework of the region, evolution of magmas, development of calderas, modeling of hydrothermal systems, and many other topics.

The findings of the past five years are briefly summarized here, together with a listing of studies in broad categories, identification of areas of special interest to National Park Service scientists and managers, identification of some trends, and a listing of publications for that period. The number of geological investigations increased steadily between 1975 and 1980, but decreased by 40 per cent last year [1981].