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 6,178 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
• • 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