Crater Lake geology

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
    • 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 6,173 feet above sea level
  • maximum depth 1,943 feet
  • deepest lake in US
  • second deepest in North America
  • ninth deepest in the 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 streams 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
    • 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

Last updated: January 23, 2021

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Crater Lake National Park
PO Box 7

Crater Lake , OR 97604


541 594-3000

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