Chaos Crags
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Chaos Crags is the youngest volcanic plug dome in Lassen Volcanic National Park, having been formed by at least four dacite domes 1200 years ago. The crags are located north of Lassen Peak.
From the base of the crags and extending toward the northwest corner of the park is Chaos Jumbles, a rock avalanche, which was set off by a phreatic eruption that undermined Chaos Crags' northwest slope 300 years ago. Riding on a cushion of compressed air (see air-layer lubrication), the rock debris traveled at about 100 miles per hour, flattened the forest before it, and dammed Manzanita Creek, forming Manzanita Lake.
In 1974 the United States Park Service took the advice of the USGS and closed the visitor center and accommodations at Manzanita Lake. The Survey stated that these buildings would be in the way of a rockslide from Chaos Crags if an earthquake or volcanic eruption occurred in the area.
Reference
- Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7