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 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).

History

Brokeoff Mountain, Lassen Peak, and Chaos Crags.

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.

From 1850-1851 witnesses 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 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. An aging seismograph station remains.

Geology and geography

Main article: Geology of the Lassen area

Broken face of Brokeoff Mountain

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 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).

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 1850s. 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.

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

See also

• List of nationally protected areas of the United States

External links

• USGS: Volcano Hazards of the Lassen Volcanic National Park Area (http://geopubs.wr.usgs.gov/fact-sheet/fs022-00/)
• Lassen Volcanic National Park Pictures (http://www.nationalparksgallery.com/parks/Lassen-Volcanic-National-Park)
• USGS: Geology of Lassen Volcanic National Park (http://wrgis.wr.usgs.gov/docs/parks/lassen/index.html)
• Photos of Lassen Volcanic National Park - Terra Galleria (http://www.terragalleria.com/parks/np.lassen-volcanic.html)
• Photographic virtual tour of Lassen Volcanic National Park. (http://www.Untraveledroad.com/USA/Parks/Lassen.htm)