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As a child, volcanoes fascinated me. Ironically, on the morning of May 18, 1980, I was with a friend driving from the Oregon Coast back to Boise. We had just escaped Portland’s morning rush hour and were heading east on the freeway near Multnomah Falls when we noticed the strangest cloud to the north. It looked atomic. But we were listening to mix tapes and didn’t bother turning on the radio till we’d almost gotten home. I was shocked and disappointed to realize we’d driven right past the volcanic eruption of Mt. St. Helens. The mountain continued to shudder and spew steamy bits of breath for several years after the eruption and I followed its gymnastics from 500 miles away.

Three hundred miles to the south and nearly 8,000 years earlier, the 12,000 foot peak of Mount Mazama exploded with something like 42 times the power of Mt. St. Helen’s eruption. One to three miles beneath the surface, the churning magma chamber was disturbed by the Juan de Fuca tectonic plate grinding under the North American plate; The chamber spat out approximately 12-miles-worth of magma and pyroclastic material, causing the roof of the magma chamber that supported Mazama to collapse and create the bowl that we now call Crater Lake. Geologists theorize that the collapse took anywhere from a few hours to perhaps days. Ash traveled north as far as central Canada. Evidence of Mazama ash has even been identified in ice cores from Greenland.

It took about two and a half centuries for precipitation to fill the caldera to its present depth of 1,943 feet—the deepest lake in North America. Oddly, there are no rivers feeding or draining the lake and precipitation amounts double evaporation rates. Water seeps through porous caldera walls at about two million gallons and hour! The rim of the caldera is approximately 5 miles by 6 miles across and 4,000 feet deep from rim to lake floor. A cinder cone called Wizard Island erupts from the water marking later, smaller eruptions within the caldera. The last known eruption was 4,800 years ago.

The Makala people, ancestors of Klamath tribes, explained the explosion of Mt. Mazama as a battle between the spirit of the sky and the spirit of the mountain.

References

National Park Service. Summer/Fall 2021. Crater Lake Visitor Guides.

Oregon Explorer https://oe.oregonexplorer.info/craterlake/geology.html

U.S. Department of the Interior https://www.doi.gov/blog/12-things-you-didnt-know-about-crater-lake-national-park

USGS https://www.usgs.gov/science-support/osqi/yes/national-parks/geology-crater-lake-national-park