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Lassen Volcanic National Park is a United States National Park in central northern California. The dominant feature of the park is Lassen Peak; the largest plug dome volcano in the world and the southern-most volcano in the Cascade Range.
The area surrounding Lassen Peak is still active with boiling mud pots, stinking fumaroles, and churning hot springs. Lassen Volcanic National Park is one of the few areas in the world where all four types of volcano can be found (plug dome, shield, cinder cone, and strato).
The park is accessible via California State Routes CA-89 and CA-44. CA-89 goes through the park.
Native Americans have inhabited the area long before white settlers first saw Lassen. The natives knew that the peak was full of fire and water and thought that it would one day blow itself apart.
Inconsistent newspaper accounts reported by witnesses from 1850-1851 described seeing "fire thrown to a terrible height" and "burning lava running down the sides" in the area of Cinder Cone. As late as 1859 a witness reported seeing fire in the sky from a distance, attributing it to an eruption. Early geologists and volcanologists who studied the Cinder Cone concluded the last eruption occurred between 1675 and 1700. After the eruption of Mt. St. Helens in 1980, the USGS began reassessing the potential risk of other active volcanic areas in the Cascade Range. Further study of Cinder Cone estimated the last eruption occurred between 1630 and 1670.
Brokeoff Mountain, Lassen Peak, and Chaos Crags. The area of Lassen Peak that was lost during the 1914-15 volcanic event is clearly visible in this picture.
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. An aging seismograph station remains.
Climate
Since the entire park is located at medium to high elevations, the park generally has cool-cold winters and warm summers below 7500 ft. Above this elevation, the climate is harsh and cold, with cool summer temperatures. Precipitation within the park is high to very high due to a lack of a rain shadow from the Coast Ranges. The park gets more precipitation than anywhere in the Cascades south of the Three Sisters. Snowfall at the Lassen Peak Chalet at 6700 ft. is around 430 inches despite facing east. Up around Lake Helen, at 8200 ft. the snowfall is around 600-700 inches, making it probably the snowiest place in California. In addition, Lake Helen gets more average snow accumulation than any other recording station in the Cascade range, with a maximum of 178 inches. ([link]).
Map of Lassen area showing hydrothermal features (red dots) and volcanic feature or remnant (yellow cones). Also shown is the outline of Brokeoff Volcano.
Lassen Peak is made of dacite and is the world's largest lava 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 Tehama 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 Brokeoff Mountain 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).
Broken face of Brokeoff Mountain
The magma that fuels the volcanoes in the park is derived from subduction off the coast of Northern California.
Cinder Cone and the Fantastic Lava Beds, located about 10 miles northeast of Lassen Peak, is a cinder cone volcano and associated lava flow field that last erupted about 1650. It created a series of basaltic andesite to andesite lava flows known as 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.
During ice ages, glaciers have modified and helped to erode the older volcanoes in the park. The center of snow accumulation and therefore ice radiation was Lassen Peak, Red Mountain, and Raker Peak. These volcanoes thus show more glacial scarring than other volcanoes in the park.
Reference
Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7
