Geologic – 03 Physiography

Crater Lake National Park: Geologic Resources Management Issues Scoping Summary


Crater Lake National Park is located in the Cascade Physiographic province. The Cascade Range is composed almost entirely of volcanic cones, vents and lava flows. It extends north into southern British Columbia – Mt. Garibaldi is the northernmost volcano – and south to Lassen Peak in California, the southernmost volcano. In Oregon the crest of the range averages about 5,000 feet, although the highest peaks are Mt. Hood at 11,360 feet, Mt. Jefferson at 10, 495 feet and South Sister at 10,354 feet (Baldwin, 1976). The highest volcanoes in the Cascade Range are Mount Rainier in Washington at 14,411 feet and Mount Shasta just north of Lassen at 14,161 feet. The USGS has identified 13 potentially active volcanoes in the Cascade Range of the U.S. Pacific Northwest, 11 of which have erupted in the last 4,000 years and 7 in the past 200 years (Dzurisin, et. al.,1999).

The Cascades are divided into the Western Cascades and the High Cascades. The Western Cascades are composed of older Tertiary (Late Eocene to Late Miocene) flows, tuffs, and intrusives. The High Cascades include the high peaks such as Mt. Hood, Mt. Jefferson, and South Sister that have erupted more recently. Deposits are almost entirely late Miocene to Holocene age (Baldwin, 1976). The eastern slope is steeper and more abrupt than the more gently sloping Western Cascades.

At a maximum depth of 1,932 feet, Crater Lake is the deepest lake in the United States, the second deepest in the Western Hemisphere, and the seventh deepest in the world. Average depth is about 1,500 feet. The surface elevation is 6,176 feet and the highest point on the rim (Hillman Peak) is 8,056 feet. Wizard Island is a small cone rising 764 feet above the surface of the water and has an elevation of 6,940 feet. The highest point in the park is 8,926 feet at Mount Scott, a parasitic cone from Mount Mazama, the volcano that formed Crater Lake.


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