Lassen Volcanic National Park

From Wikipedia, the free encyclopedia

Lassen Volcanic National Park
IUCN Category II (National Park)

Location:	California, USA
Nearest city:	Redding, CA
Coordinates:	40°29′17″N, 121°30′18″W
Area:	106,000 acres (429 km²)
Established:	August 9, 1916
Visitation:	1,250,000 (in 2003)
Governing body:	National Park Service

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. Lassen Volcanic National Park started as two separate national monuments designated by President Theodore Roosevelt in 1907: Cinder Cone National Monument and Lassen Peak National Monument.

The source of heat for volcanism in the Lassen area was, and still is, subduction off the Northern California coast of the Gorda Plate diving below the North American Plate. 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.

1 History
2 Geography and climate
3 Geology
- 3.1 Formation of basement rocks
- 3.2 Volcanoes rise
4 See also
5 Reference
- 5.1 Major works cited
- 5.2 Notes
6 See also
7 External links

[edit] History

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.^[1]

White immigrants in the mid 19th century used Lassen Peak as a landmark on their trek to the fertile Sacramento Valley. One of the guides to these immigrants was a Danish blacksmith named Peter Lassen, who settled in Northern California in the 1830s. Lassen Peak was named after him.^[1] Nobles Emigrant Trail was later cut through the park area and passed Cinder Cone and the Fantastic Lava Beds.

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.

The Lassen area was first protected by being designated as the Lassen Peak Forest Preserve. Lassen Peak and Cinder Cone were later declared as United States National Monuments in May 1907 by President Theodore Roosevelt.^[2]

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. Fortunately, because of warnings, no one was killed, but several houses along area creeks were destroyed. Because of the eruptive activity, which continued through 1917, and the area's stark volcanic beauty, Lassen Peak, Cinder Cone and the area surrounding were declared a National Park on August 9, 1916.^[1]

The 29 mile Main Park Road was constructed between 1925 and 1931, just 10 years after Lassen Peak erupted. Near Lassen Peak the road reaches 8512 feet, making it the highest road in the Cascade Mountains. It is not unusual for 40 feet of snow to accumulate on the road near Lake Helen.

In 1974 the United States Park Service took the advice of the United States Geological Survey (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.^[1] An aging seismograph station remains.

After the 1980 eruption of Mount St. Helens, the USGS intensified its monitoring of active and potentially active volcanoes in the Cascade Range. Monitoring of the Lassen area includes periodic measurements of ground deformation and volcanic-gas emissions and continuous transmission of data from a local network of nine seismometers to USGS offices in Menlo Park, California.^[3] Should indications of a significant increase in volcanic activity be detected, the USGS will immediately deploy scientists and specially designed portable monitoring instruments to evaluate the threat. In addition, the National Park Service (NPS) has developed an emergency response plan that would be activated to protect the public in the event of an impending eruption.

[edit] Geography and climate

Map of Lassen area showing hydrothermal features (red dots) and volcanic feature or remnant (yellow cones). Also shown is the outline of Brokeoff Volcano.

The park is located near the northern end of Sacramento Valley. The western part of the park features great lava pinnacles (huge mountains created by lava flows), jagged craters, and steaming sulphur vents. It is cut by glaciated canyons and is dotted and threaded by lakes and rushing clear streams.

The eastern part of the park is a vast lava plateau more than one mile (1.6 km) above sea level. Here are found small cinder cones (Fairfield Peak, Hat Mountain, and Crater Butte).^[4] Forested with pine and fir, this area is studded with small lakes, but it boasts few streams. Warner Valley, marking the southern edge of the Lassen Plateau, features hot spring areas (Boiling Springs Lake, Devils Kitchen, and Terminal Geyser).^[4] This forested, steep valley also has large meadows that have wildflowers in spring.

Lassen Peak is made of dacite and is one of the world's largest lava domes. It is also the southernmost non-extinct volcano of the Cascade Range (specifically, the Shasta Cascade part of the range). The 10,457 foot tall 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.^[1] After emptying its throat and partially doing the same to its magma chamber in a series of eruptions, Tehama either collapsed into itself and formed a two-mile wide caldera in the late Pleistocene or was simply eroded away with the help of acidic vapors that turned hard rock into clay.

On the other side of the present caldera is Brokeoff Mountain (9,235 feet or 2,815 m), 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 7,000-8,400 feet (2,133 m- 2,560 m) 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.

Despite not having any glaciers currently, Lassen Peak does have 14 permanent snowfields ([1]).

Since the entire park is located at medium to high elevations, the park generally has cool-cold winters and warm summers below 7,500 ft. (2,286 m). 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 6,700 ft. (2,042 m) is around 430 inches (10.9 m) despite facing east. Up around Lake Helen, at 8,200 ft. (2,500 m) the snowfall is around 600-700 inches (15.24 m- 17.78 m), 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 (4.52 m).^[5] Snowbanks persist year-round.

Kings Creek with Lassen Peak on the horizon

[edit] Geology

Main article: Geology of the Lassen volcanic area

Cinder Cone from the Fantastic Lava Beds.

Lassen Peak from Devastated Area.

Lassen Peak from the summit of Brokeoff Mountain. Photo shows 1915 tongue of lava and Volcan's Eye

Lassen Peak as seen from Lake Helen

[edit] Formation of basement rocks

In the Cenozoic, uplifting and westward tilting of the Sierra Nevada along with extensive volcanism generated huge lahars (volcanic-derived mud flows) in the Pliocene which became the Tuscan Formation. This formation is not exposed anywhere in the national park but it is just below the surface in many areas.

Also in the Pliocene, basaltic flows erupted from vents and fissures in the southern part of the park. These and later flows covered increasingly large areas and built a lava plateau. In the later Pliocene and into the Pleistocene, these basaltic flows were covered by successive thick and fluid flows of andesite lava, which geologists call the Jupiter lavas and the Twin Lakes lavas. The Twin Lakes lava is black, porphyritic and has abundant xenocrysts of quartz (see Cinder Cone).

Another group of andesite lava flows called the Flatiron, erupted during this time and covered the southwestern part of the park's area. The park by this time was a relatively featureless and large lava plain. Subsequently, the Eastern basalt flows erupted along the eastern boundary of what is now the park, forming low hills that were later eroded into rugged terrain.

[edit] Volcanoes rise

Pyroclastic eruptions then started to pile tephra into cones in the northern area of the park.

Mount Tehama (also known as Brokeoff Volcano) rose as a stratovolcano in the southeastern corner of the park during the Pleistocene. It was made of roughly alternating layers of andesitic lavas and tephra (volcanic ash, breccia, and pumice) with increasing amounts of tephra with elevation. At its height, Tehama was probably about 11,000 feet high.

Approximately 350,000 years ago its cone collapsed into itself and formed a two-mile wide caldera after it emptied its throat and partially did the same to its magma chamber in a series of eruptions. One of these eruptions occurred where Lassen Peak now stands, and consisted of fluid, black, glassy dacite, which formed a layer 1500 feet thick (outcroppings of which can be seen as columnar rock at Lassen's base).

During glacial periods (ice ages) of the present Wisconsinan glaciation, glaciers have modified and helped to erode the older volcanoes in the park, including the remains of Tehama. Many of these glacial features, deposits and scars, however, have been covered up by tephra and avalanches, or were destroyed by eruptions.

Roughly 27,000 years ago (older data gave an age of 18,000 years), Lassen Peak started to form as a dacite lava dome quickly pushed its way through Tehama's destroyed north-eastern flank. As the lava dome pushed its way up, it shattered overlaying rock, which formed a blanket of talus around the emerging volcano. Lassen rose and reached its present height in a relatively short time, probably in as little as a few years. Lassen Peak has also been partially eroded by Ice Age glaciers, at least one of which extended as much as 7 miles (11 km) from the volcano itself.

Since then, smaller dacite domes formed around Lassen. The largest of these, Chaos Crags, is just north of Lassen Peak. Phreatic (steam explosion) eruptions, dacite and andesite lava flows and cinder cone formation have persisted into modern times.

[edit] See also

[edit] Reference

[edit] Major works cited

Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7
Volcano Hazards of the Lassen Volcanic National Park Area, California, U.S. Geological Survey Fact Sheet 022-00, Online version 1.0 (adapted public domain text; accessed 25 September 2006)

[edit] Notes

^ ^a ^b ^c ^d ^e Geology of National Parks, page 466
^ Geology of U.S. Parklands, page 154
^ USGS: Volcano Hazards of the Lassen Volcanic National Park Area, California
^ ^a ^b "Geology Fieldnotes for Lassen Volcanic National Park California" (accessed 7 October 2006)
^ Skimountaineer.com: Cascade Snow