Abstract

The Crater Lake depression is the surface expression of the Crater Lake collapse structure. The structure comprises 2 main concentric fault zones forming an inner and outer cylinder of collapse beneath Crater Lake. The inner cylinder, which is about 300 ft (~100 m) in diameter, was down faulted about 140 ft (~43 m) in Late Cretaceous – Tertiary – Early Pleistocene time and the outer cylinder, which is about 700 ft (~213 m) in diameter, was downfaulted 50 to 100 ft (15 – 30 m) during the last deglaciation about 13 600 years ago. The Crater Lake structure was formed presumably by collapse as a result of the removal of salt from the Prairie Evaporite Formation by groundwater.

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