July 14, 2009 • Did You Know: Lassen Peak

Publisher’s note: This Did You Know column originally appeared in the Tuesday, July 14, 2009 edition of the Lassen County Times.

Lassen Peak is the largest of a group of more than 30 volcanic domes erupted that has over the past 300,000 years in Lassen Volcanic National Park.

On the evening of May 14, 1915, incandescent blocks of lava could be seen bouncing down the flanks of Lassen Peak from as far away as the town of Manton, 20 miles to the west.

Eight days later on May 22, 1915, an explosive eruption occurred at Lassen Peak, the southernmost active volcano in the Cascade Range, devastating nearby areas and raining volcanic ash as far away as 200 miles to the east. This explosion was the most powerful in a series of smaller eruptions from 1914-1917 that were the most recent to occur in the Cascades prior to the 1980 eruption of Mt. St. Helens.

Volcanoes in the Lassen area tend to erupt infrequently, and may be inactive for periods lasting centuries or even millennia. The most recent large eruption produced Chaos Crags about 1,100 years ago.

Such large eruptions in the Lassen area have an average recurrence interval of about 10,000 years. However, the geologic history of the Lassen area indicates that volcanism there is episodic, having periods of relatively frequent eruptions separated by long quiet intervals. For example, the last large event before the Chaos Crags eruption was the one that built Lassen Peak 27,000 years ago.