A Walk Along a Geologic Timeline #3 - California
Posted by: 
Volcanoguy
N 40° 26.257 W 121° 32.009
10T E 624380 N 4477362
Rock display at Kohm Yah-mah-nee Visitor Center
Waymark Code: WMJR73
Location: California, United States
Date Posted: 12/22/2013
Views: 2
One of four large volcanic boulders around the Kohm Yah-mah-nee Visitor Center near the south entrance to Lassen Volcanic National Park.
Text of display sign:
The Formation of Chaos Crags Dome and Chaos Jumbles
This rhyodacite boulder was created about 1,100 years ago — it was part of a cinder cone volcano in the Chaos Crags area. Rhyodacite is fine-grained and, like granite, contains quartz.
Chaos Crags was a tephra (cinder) volcano that formed a dome over its vent about 1,100 years ago. About 1,000 years ago Chaos Crags erupted violently. The eruptions were followed by episodes of dome growth and collapse. About 700 years later a rock-fall avalanche caused one of Chaos Crag’s domes to partially collapse, creating an impressive avalanche deposit known as Chaos Jumbles.
Type of Display: Geological
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