Lassen Volcanic National Park

From 1850-1851 wittinesses reported seeing ash, steam, and ejected volcanic cinders in the area of Cinder Cone. For many years these eruptions were attributed to Cinder Cone, but more recent geologic studies studies of the volcano indicate that it last erupted much earlier.

Lassen Peak and Cinder Cone were declared United States National Monuments in 1907 by President Theodore Roosevelt.

Starting in May 1914 and lasting until 1921, a series of minor to major eruptions occurred on Lassen. These events created a new crater, and released lava and a great deal of ash. Amid this volcanic activity, Lassen Volcanic National Park was created on August 9, 1916.

In 1974 the United States Park Service took the advice of the USGS and closed the visitor center and accommodations at Manzanita Lake. The Survey stated that these buildings would be in the way of a rockslide from Chaos Crags if an earthquake or eruption occurred in the area.

View of Lassen Peak from Cinder Cone
(larger version)

The heat that fuels the volcanoes in the park is derived from subduction off the coast of Northern California

Lassen Peak is made of dacite and is the world's largest volcanic dome. The volcano sits on the north-east flank of the remains of Mount Tehama, a stratovolcano that was a thousand feet higher than Lassen and 11 to 15 miles wide at its base. After emptying its throat and partially doing the same to its magma chamber in a series of eruptions, Tehama collapsed into itself and formed a two-mile wide caldera in the late Pleistocene. Since that time the remains of Tehema have been heavily eroded.

On the other side of the present caldera is Brokeoff Mountain (9235 feet), which is an erosional remnant of Mount Tehama and the second highest peak in the park. Mount Conrad, Mount Diller, and Pilot Pinnacle are also remnant peaks around the caldera.

Sulphur Works is a geothermal area in between Lassen Peak and Mount Brokeoff that is thought to mark an area near the center of Tehama's now-gone cone. Other geothermal areas in the caldera are Little Hot Springs Valley, Diamond Point (an old lava conduit), and Bumpass Hell (see Geothermal areas in Lassen Volcanic National Park).

Cinder Cone, located about 10 miles northeast of Lassen Peak, is a cinder cone volcano that was probably created in two eruptions of ash and volcanic cinders in the 1650s. It was made inactive by a series of basalt lava flows that created the Fantastic Lava Beds.

There are four shield volcanoes in the park; Mount Harkness (southwest corner of the park), Red Mountain (at south-central boundary), Prospect Peak (in northwest corner), and Raker Peak (north of Lassen Peak). All of these volcanoes are 7000-8400 feet above sea level and each are topped by cinder cone volcanoes.