Crater Lake lies in a volcanic depression called a caldera that formed when the top of the Cascade volcano known as Mount Mazama collapsed during an enormous explosive eruption about 7,700 years ago. This cataclysmic event was followed by a series of post-caldera eruptions until about 5,000 years ago. These smaller events erupted lava flows, a lava dome, and tephra from vents on the caldera floor. Such activity built Wizard Island (above) on the western caldera floor.

A new report describes the various types of volcano and earthquake hazards in the Crater Lake area, estimates the likelihood of future events, suggests ways to reduce risk, and includes a map of hazard zones. Crater Lake does not directly threaten a large population center, but its future activity does pose a hazard to facilities and people at Crater Lake National Park. About 500,000 people visit the park each year, most during the summer months.

This report is based on many USGS studies of the history of Mount Mazama and Crater Lake, including geologic mapping of the volcano and caldera walls, lake-floor studies with a manned submersible, and numerous topical investigations relating to the accumulation and eruption of a shallow magma body beneath the volcano.

The report USGS Open-File Report 97-487 can be viewed online or, if you would like a copy, it can be ordered from the U.S. Geological Survey.

URL of this document: http://volcanoes.usgs.gov/About/Highlights/CraterlakeHaz/highlight.html
Last modified: September 30, 1998