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Chaos Crags and Chaos Jumbles

Chaos Crags, located northwest of Lassen Peak, erupted 1,100 years ago and is the youngest unit of the Eagle Peak sequence. As mapped by Christiansen and others (2002), the eruptive sequence consists of a group of six rhyodacite lava domes and associated pyroclastic deposits that define a typical silicic eruption in the Lassen Volcanic Center.

Initial activity included formation of a tephra cone, emplacement of two pyroclastic flows, and growth of a dome that plugged the vent. After a quiet interval of approximately 70 years, the dome (dome A) was destroyed by a violent eruption that resulted in a pyroclastic flow and an air- fall tephra deposit. These deposits are best seen in the drainages of Manzanita and Lost Creeks within 10 km (6.2 mi) of the Chaos Crags. This violent eruption was followed by the growth of 5 domes, 2 of which had hot, dome-collapse avalanches.

Chaos Jumbles formed around 340 years ago when one of the domes collapsed in a series of 3 cold rockfall-avalanches. This series of avalanches was the result of slope instability and not did not occur as the result of an eruptive process. As it moved down slope, the mass of rock and debris from Chaos Crags was cushioned underneath by a pocket of air. This air pocket reduced underlying friction, therefore acting as a kind of lubricant, and enabled the avalanche to rush across the valley very quickly. The debris flowed more than 120 m (400 ft) up the side of Table Mountain on the opposite side of the valley from Chaos Crags.