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Mount Mazama (known today as Crater Lake National Park, Oregon) erupted violently 7,700 years ago leaving an impressive crater where the mountain once stood. A blanket of volcanic ash from the eruption was deposited downwind - a well-known time marker for geologists throughout the Pacific Northwest.
This 3-minute video - Mazama Ash - features a site where the famous ash is exposed in Johnson Canyon, right next to heavily-traveled Interstate 90 in central Washington. No other ash bed - including the 1980 Mt St Helens ash layer - rivals the Mazama for regional thickness. The Mazama is found through the Northwest, including under the waves of the Pacific Ocean. The 7,700 year-old ash layer has been consistently found in submarine canyons beneath 13 underwater landslide deposits created by 13 great earthquakes since the Mazama eruption.
Tom Foster (HUGEfloods.com) and Nick Zentner (Central Washington University) have been hiking together in eastern Washington for years. ‘Mazama Ash’ is part of an "I-90 Rocks” geology video series.