Geology and History

Lassen Volcanic Center is located at the southern edge of the Cascade Range, which is bounded on the west by the Sacramento Valley and the Klamath Mountains, on the south by the Sierra Nevada, and on the east by the Basin and Range geologic provinces.

Over the last 3 million years, regional volcanism in the Lassen segment of the Cascade arc constructed a broad platform of volcanic rocks. In periods of about 50,000 - 200,000 years, concentrated volcanism occurred in localized areas. These "volcanic centers" are defined as large, long-lived edifices erupting the full range of lava compositions from basalt to rhyolite.

Volcanic centers within the southernmost Cascade Range are regions of large, long-lived, volcanic activity that erupt the full range of magma types (from low- silica basalt to high-silica rhyolite). They form when large bodies of basalt magma, which is very close to the composition of the mantle, rise through and collect in the crust.

On May 22, 1915, an explosive eruption at Lassen Peak, California, the southernmost active volcano in the Cascade Range, devastated nearby areas and rained volcanic ash as far away as 300 km (about 200 mi) to the east. This explosion was the most powerful in a 1914-17 series of eruptions that were the last to occur in the Cascades before the 1980 eruption of Mount St. Helens.

Cinder Cone, a 215 m (700 ft) tall volcanic cone located in the northern part of Lassen Volcanic National Park, is the youngest mafic volcano in the Lassen region and the second youngest eruption in the Twin Lakes sequence.

Chaos Crags, located northwest of Lassen Peak, erupted 1,100 years ago and is the youngest unit of the Eagle Peak sequence.

All four types of volcanoes found in the entire world are represented in Lassen Volcanic National Park— shield (Prospect Peak), plug dome (Lassen Peak), Cinder Cone (Cinder Cone), and Composite (Brokeoff Volcano) volcanoes.