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Landslides and Rockfalls at Lassen Volcanic Center

There are landslide and rockfall hazards at Lassen that are not directly related to eruptions. Approximately 350 years ago, collapse of one of the Chaos Crags domes generated huge rockfalls, creating an area now called the Chaos Jumbles. The first and largest of these traveled over 6 km (4 mi) downslope and was able to climb 120 m (400 ft) up the side of Table Mountain. The trigger for the rockfall is unknown, but it was most likely a large earthquake. Normal weathering also weakens fractured volcanic rock and contributes to small rockfalls. In the summer of 1994, a rockfall of 10,000 m3 (13,000 yards3, or about the volume of 500 minivans) occurred on the northeastern flank of Lassen Peak.