Mazama Ash Deposits
January 19, 2004
The photo above shows thick deposits of Mount Mazama ash near Crater Lake, Oregon. Approximately 7,800 years ago, a large stratovolcano now referred to as Mount Mazama, in the southern Oregon Cascade Range, erupted and spewed ash over much of western North America. The eruption led to the formation of a 5-mile (8 km) diameter caldera that subsequently filled with water from rain and snowmelt. We now know it as Crater Lake, and it's located in one of the oldest national parks in the U.S. (founded in 1902). The lake is the deepest in North America, one of the clearest, and has an alluring blue color. During the eruption, massive pumice ash flows swept down the steep flanks of the volcano at over 100 miles (160 km) an hour. These flows swept up huge trees that became imbedded in the incandescent ash, which was over 800 degrees F. Eventually, the trees (logs) were turned into charcoal in this anaerobic environment. As one drives toward the dormant volcano along the upper regions of the spectacular Rogue River, on occasion these ancient, blackened logs can be identified in the deep road cuts.