Geologic features of Crater Lake National Park:
Mount Mazama
- the eruption of Mount Mazama, about 7,700 years ago, lasted only a couple of days
- the first phase of the eruption produced a towering column of pumice and ash
- the second phase of the eruption was the ring-vent phase that started the collapse of the mountain into the center
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- pyroclastic flows happened in this phase (mixture rock fragments, gas, ash at temperatures > 1470 degrees F)
Mazama Ash
- ash rose and settled over much of the western US and southwestern Canada (656,000 miles squared)
- the ash makes a good marker for geologists to study features and processes over a wide variety of landscapes
Shield Volcanoes and Cinder Cones
- partly surround Mount Mazama
- part of the historic magma input to Mount Mazama
- activity of these small volcanoes represents activities of regional volcanism
Crater Lake Caldera and rocky fill
- the caldera is 5-6 miles in diameter
- the caldera is 3,900 feet deep
- since the eruption, material has fallen into the caldera from the walls, and from new volcanic activity inside the caldera
Crater Lake
- average surface elevation 6,178 feet above sea level
- maximum depth 1,949 feet
- deepest lake in US
- second deepest in North America
- seventh deepest in with world
- the lake is one of the most clear in the world
- the blue color of the lake is one of the treasures of the world
- scientific study began as early as 1887
- the lake has no stream running in or out
- the lake water level is controlled by precipitation, evaporation, and seepage through the rocks
Glacial Features
- in the past, glaciers and volcanoes occurred at Crater Lake during the known global ice ages
- glacial features include
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- ice-bounded lava flow formations
- table mountains
- till and moraines
- polish and striations
- U-shaped valleys
- notches, cirques, and horns
- six advances of glacial ice occurred at Crater Lake National Park
- carved notches at the beginnings of Sun and Kerr valleys
- one advance happened on the caldera walls
Caves
- the park contains more than 40 caves
- 31 caves are within the rim of the caldera
- many caves are near the lake surface
- 5 cave sites (with one or more caves) occur outside the rim
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