Geologic Map of Mount Mazama and Crater Lake Caldera, Oregon

U.S. Geological Survey

Crater Lake partly fills one of the most spectacular calderas of the world, an 8-by-10-kilometer (5-by-6.2-mile) basin more than 1 kilometer (0.6 mile) deep formed by the collapse of the volcano known as Mount Mazama during a rapid series of explosive eruptions about 7,700 years ago. Having a maximum depth of 594 meters (650 yards), Crater Lake is the deepest lake in the United States. Crater Lake National Park, dedicated in 1902, encompasses 645 square kilometers (250 square miles) of pristine forested and alpine terrain, including the lake itself, virtually all of Mount Mazama, and most of the area of this geologic map.

The geology of the area was first described in detail by J. S. Diller and H. P. Patton in 1902. In 1942, famed volcanologist Howel Williams published a vivid account of his geological investigations that led to international recognition of Crater Lake as the classic collapse caldera.

Because of excellent preservation and access, Mount Mazama, Crater Lake caldera, and the deposits formed by the climactic eruption constitute a natural laboratory for study of volcanic and magmatic processes.

A detailed bathymetric survey of the floor of Crater Lake in 2000 provides a unique record of postcaldera eruptions, the interplay between volcanism and filling of the lake, and sediment transport within this closed basin. Knowledge of the geology and eruptive history of the Mount Mazama edifice, greatly enhanced by the caldera wall exposures, gives exceptional insight into how large volcanoes of magmatic arcs grow and evolve and what hazards they may pose.

This map is unusual because it portrays bedrock (outcrop), surficial, and lake floor geology, revealing the geomorphology and geologic history of Crater Lake both above and below the water line. This map and its GIS database serve as the framework for investigations of volcanic and magmatic processes and to evaluate natural hazards in the Crater Lake region.

Courtesy of U.S. Geological Survey.

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