Geological History of Crater Lake National Park

Wizard Island, Crater Lake, Crater Lake Nation...

Wizard Island, Crater Lake, Crater Lake National Park, Oregon in 2011 (Photo credit: Wikipedia)

As far as lakes go, Crater Lake is a big one . . . the deepest in the United States, the seventh deepest in the entire world. The geological history of Crater Lake is an exciting one, filled with tales of the Earth’s crust folding and uplifting, volcanoes erupting and collapsing, volcanoes within volcanoes . . . yep, it sure is exciting stuff.

Crater Lake National Park is past of the Cascade Mountain Range which was formed as the Earth’s crust was folded and uplifted and pushing seas westerly, running all the way from Mount Garibaldi in Canada, right through to Lassen Peak, found in northern California. Violent eruptions were witnessed on the surface, along with lava welling up through enormous cracks as they were formed. One of the great volcanoes, Mount Mazama, holds Crater Lake.

Crater Lake actually lies on top of Mount Mazama, delving deep inside this ancient volcano by almost 2,000 feet. Long before Crater Lake was created, Mount Mazama produced gigantic volcanic eruptions amid long periods of quiet, for around half a million years. The accumulation of cinders, ash and pumice meant that Mount Mazama grew to an enormous height, round about 12,000 feet, with Hillman Peak and Mount Scott being created as parasitic cones on the flanks of Mount Mazama. Glaciers covered Mount Mazama also, from time to time (as glaciers do) carving out the valleys like Kerr Notch and Munson Valley. Fast forward to around 7,700 years ago and there was one almighty climatic eruption of Mount Mazama which scattered ash over an incredible eight states as well as three provinces in Canada . . . some 5,000 square miles was covered with around 6 inches of ash from Mount Mazama. As you can imagine that’s an awful lot of ash, the magma chambers of Mount Mazama were left empty and the volcano subsequently collapsed leaving an enormous caldera. Bye bye high mountain, hello deep hole . . . . At first the floor of the caldera was way too hot to be able to hold water, but extra volcanic activity sealed the holes, building what was to become Wizard Island and Merriam, volcanoes within volcanoes.

Ha ha, you could make your very own caldera . . . just don’t tell your Mom it was my idea when she has to clean up the mess.

Shall we take a closer look at the stages which eventually lead to the collapse of Mount Mazama, after all, it is a pretty unique occurrence . . . okay, you talked me into it!

  • We’ll start around 420,000 years ago, when Mount Mazama was going through a bit of a “growth spurt” and created Mount Scott. At this point Mount Mazama may have reached dizzying heights of around 12,000 feet.
  • Moving on to 7,000 years ago, the mother of all eruptions occurred ejecting a column of hot gas and magma high up into the air.
  • Other eruptions around Mount Mazama produced very fast moving flows of hot ash, until eventually the magma chamber was empty, the foundations of Mount Mazama were gone and the walls of the huge volcano began collapsing. What took thousands of years to create simply disappeared almost overnight, well, overnight in geological terms anyway, and probably only a few days in real terms.
  • A caldera was formed by the collapse (have you watched the video above about how to recreate your very own caldera . . . looks like fun), eventually water and rainfall began to fill the caldera creating the deepest lake in the nation, an incredible 1,932 feet.

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