DESCRIPTION:
Lassen Peak Volcano, California

Lassen82_lassen_peak_and_kings_creek_10-82.jpg
Lassen Peak, California, and Kings Creek Meadows, Lassen Volcanic National Park.
USGS Photograph taken in October 1982 by Lyn Topinka
[medium size] ... [large size]

Lassen Volcanic Center

Location: California

Latitude: 40.492 N

Longitude: 121.508 W

Height: 3,187 Meters (10,457 Feet)

Type: Stratovolcano Volcanic Dome

Number of eruptions in past 200 years: 1 ²

Latest Eruptions: 1914-1917 ² ... 1914-1921 ³.

Present thermal activity: Small steaming -- fumaroles in summit craters; hot ground on northern flank.

Remarks: Lateral blast occurred in last eruption ² ... One of the youngest major Cascade volcanoes. Most of the mountain is a single mass of dacite rock, emplaced in a relatively short time. Only volcano in the 48 conterminous United States, besides Mount St. Helens, to have erupted in the 20th century ³.

Before the 1980 eruption of Mount St. Helens in Washington, Lassen Peak was the most recent volcanic outburst in the contiguous 48 states. The peak is the southernmost volcano in the Cascade Range which extends from here into Canada. 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 spectacular glaciated canyons and is dotted and threaded by lakes and rushing clear streams. Snowbanks persist year-round and beautiful meadows are spread with wildflowers in spring. The eastern part of the park is a vast lava plateau more than one mile above sea level. Here are found small cinder cones (Fairfield Peak, Hat Mountain, and Crater Butte). 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). This forested, steep valley also has gorgeous large meadows. ...

The Lassen geothermal area -- Sulphur Works, Bumpass Hell (largest), Little Hot Springs Valley, Boining Springs Lake, Devils Kitchen, and Terminal Geyser -- offer bubbling mud pots, steaming fumaroles, and boiling water. Some of these thermal features are getting hotter.

History here generally describes the period from 1840, even though Jedediah Smith passed through in 1828 on his overland trek to the West Coast. California's gold rush brought the first settlers. Two pioneer trails, developed by William Nobles and Peter Lassen, are associated with the park. In 1851, Nobles discovered an alternate route to California, passing through Lassen. Sections of the Lassen and Nobles Emigrant Trail are still visible. Lassen, for whom the park is named, guided settlers near here and tried to establish a city. Mining, power development projects, ranching, and timbering were all attempted. The area's early federal protection saved it from heavy logging.

Peter Lassen is the namesake of the County. He was a Danish emigrant who came to California in 1840 and spent his last years prospecting the Honey Lake Valley. He was murdered in 1859 on an expedition in the Black Rock Desert.

Peter Lassen opened the Lassen Emigrant Trail in 1848 when he led a 12-wagon emigrant train from Missouri to California. The route was extensively traveled during the years 1848-53 by emigrants seeking gold, adventure, and a new life in the west - but because of the hardships of the route and the hostility of the Indians, the trail was little used after 1853.

The Lassen region has been volcanically active for more than 3 million years. The Lassen "volcanic center" began to erupt about 600,000 years ago. From 600,000 to 400,000 years ago, eruptions built a large volcano, often referred to as "Brokeoff Volcano" or "Mount Tehama". Later, this volcano became inactive and was mostly eroded away, leaving remnants that include Brokeoff Mountain, Mount Conard, Mount Diller, and Diamond Peak. Subsequent eruptions in the Lassen volcanic center have formed more than 30 steep-sided lava domes (the Lassen dome field). The most recently active parts of the volcanic center are Lassen Peak and other young domes formed in the past 50,000 years.

The Lassen volcanic center in Lassen Volcanic National Park consists of an andesitic stratovolcano, a dacite dome field, and peripheral small andesitic shield volcanoes. Lassen's long and complex eruptive history is a 600,000-year-long record of volcanism associated with the generation, rise, emplacement, and evolution of a plutonic magma body in the crust.

The evolution of the Lassen volcanic center began with the construction of Brokeoff volcano, an andesitic stratovolcano. Glacial erosion, enhanced by hydrothermal alteration of permeable cone rocks, has resulted in deep erosion of Brokeoff volcano. The major erosional remnants, Brokeoff Mountain, Mount Diller, Mount Conard, and Diamond Peak, enclose a central depression that marks the position of Brokeoff volcano, which was approximately 3,350 meters high, had a basal diameter of approximately 12 kilometers, and a volume of about 80 cubic kilometers. Potassium-argon ages of lavas from Brokeoff volcano range from 0.59-0.39 million years ago. Thus, Brokeoff was active for approximately 200,000 years. ...

Coincident with the extinction of Brokeoff volcano was a major change in the character of volcanism at the Lassen volcanic center. Activity shifted to the north flank of Brokeoff volcano and became more silicic and episodic. Three sequences of silicic lavas and a group of hybrid lavas were erupted in the last 400,000 years. A conspicuous feature of the lavas of the dacite dome field is the ubiquitous presence of blobs of quenched andesitic magma, formed by samll amounts of andesite mixing into the silicic magma system.

The first expression of the silicic magma system was eruption of small rhyodacite lava flows and a rhyolite dome at 400,000 years ago. They were quickly followed by eruption of more than 50 cubic kilometers of rhyolitic magma as air-fall tephra and ash flows. This eruption is thought to have produced a small caldera on the northern flank of Brokeoff volcano that is now filled by two subsequent sequences of lava comprising the dacitic dome field. The lavas of the early sequence are best preserved on Raker Peak and Mount Conard. The ash flows are preserved only to the west in the Manton area; the air-fall tephra is widely recognized in nearby states.

The second and third sequences of lavas at the Lassen volcanic center comprise the dacite dome field. The second sequence erupted from 250,000-200,000 years ago ... produced a cluster of 12 lava domes and associated thick flows with a total volume of approximately 15-25 cubic kilometers. The vents for these lavas were concentrated along the inferred edge of the caldera on the north flank of Brokeoff volcano. Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak are the most prominent domes. ... The third sequence consists of porphyritic hornblende-biotite rhyodacite erupted as lava domes, short thick lava flows, and pyroclastic flows erupted in at least 12 episodes during the past 100,000 years. Rocks of this sequence form the northern and western portions of the dacite dome field, and their vents are concentrated in linear chains near the inferred western edge of the old caldera. The most prominent features of this sequence are Eagle Peak (55,000 years ago), Sunflower Flat domes (35,000 years ago), Lassen Peak (approximately 25,000 years ago), and Chaos Crags (1,050 years ago). ...

A group of hybrid andesite lavas, called quartz basalt by previous geologists, are associated with the silicic lavas. They form lava-flow complexes with agglutinate cones marking their vents. ... A volume of approximately 10 cubic kilometers of hybrid andesite erupted around the margins of the dacite dome field in ten episodes over the last 300,000 years. Hat Mountain, Raker Peak, and Cinder Cone are the most prominent features. The products of the 1915 eruption of Lassen Peak belong to this sequence.

Three episodes of volcanism have occurred at the Lassen volcanic center in the past 1,100 years. These are the complex eruption at Chaos Crags, the eruptions at Cinder Cone, and the summit eruptions of Lassen Peak in 1914-1917. ...

The Lassen region has been volcanically active for more than 3 million years. The Lassen "volcanic center" began to erupt about 600,000 years ago. From 600,000 to 400,000 years ago, eruptions built a large volcano, often referred to as "Brokeoff Volcano" or "Mount Tehama". Later, this volcano became inactive and was mostly eroded away, leaving remnants that include Brokeoff Mountain, Mount Conard, Mount Diller, and Diamond Peak. Subsequent eruptions in the Lassen volcanic center have formed more than 30 steep-sided lava domes (the Lassen dome field). The most recently active parts of the volcanic center are Lassen Peak and other young domes formed in the past 50,000 years.

About 600,000 years ago a great Pacific Ring of Fire stratovolcano (Mount Tehama) gradually built up here through countless erutpions. Before Lassen Peak was emplaced, Mount Tehama had collapsed, but its caldera was breached and no lake developed as did Crater Lake in Oregon. Mount Tehama's main vent was probably what is now the park's Sulphur Works. Remnants of its caldera flanks are Brokeoff Mountain, Mount Diller, Pilot Pinnacle, and Mount Conrad. Connect these peaks in a circle to envision Mount Tehema's base - more than 11 miles wide.

Lassen Peak 1914 Eruption Information

Because geologically recent volcanic activity in an area is the best guide to forecasting future eruptions, scientists study the lava flows, ash, and other deposits from past eruptions. Volcanoes in the Lassen area tend to erupt infrequently, and may be inactive for periods lasting centuries or even millennia. The most recent eruptions in the Lassen area were the relatively small events that occurred at Lassen Peak between 1914 and 1917. The most recent large eruption produced Chaos Crags about 1,100 years ago. Such large eruptions in the Lassen area have an average recurrence interval of about 10,000 years. However, the geologic history of the Lassen area indicates that volcanism there is episodic, having periods of relatively frequent eruptions separated by long quiet intervals. For example, the last large event before Chaos Crags eruption was the one that built Lassen Peak 27,000 years ago.

Lassen Peak Region:

Lava Flows: Produced at least one small lava flow in A.D. 1915.

Domes: At least eight silicic domes within the last 12,000 years, four between approximately 12,000 and 11,000 years, three approximately 1,000 years ago, and one approximately 350 years ago.

Tephra Eruptions: Tephra eruption approximately 1,100 years ago.

Pyroclastic Flows: Two pyroclastic flows between approximately 12,000 and 11,000 years ago, three pyroclastic flows approximately 1,100 years ago, and two pyroclastic flows approximately 300 years ago.

Directed Blasts: Two small directed blasts (or pyroclastic flows) in A.D.1915 - effects extend to a distance of 5 kilometers from the summit.

Debris Flows: Dozens of debris flows were generated during eruptions of Lassen Peak dome approximately 11,000 years ago, several debris avalanches approximately 300 years ago, and two small debris flows in A.D. 1915.

Lassen Peak Region Basalt Field:

Eruption of more than 20 center producing lava flows and (or) cinder cones during the last 10,000 years ... Small volumes of mafic tephra erupted at many centers during Holocene time. Around 80 square kilometers covered with fine ash from Cinder Cone about 400 years ago.

In May 1914 Lassen Peak burst into eruption, beginning a seven-year cycle of sporadic volcanic outbursts. The climax of this episode took place in 1915, when the peak blew an enormous mushroom cloud some seven miles into the stratosphere. The reawakening of this volcano, which began as a vent on a larger extinct volcano known as Tehama, profoundly altered the surrounding landscape. The area was made a National Park in 1916 because of its significance as an active volcanic landscape. The park is a compact laboratory of volcanic phenomena and associated thermal features (except true geysers). It is part of a vast geographic unit - a great lava plateau with isolated volcanic peaks - that also encompasses Lava Beds National Monument, California, and Crater Lake National Park, Oregon.

Before the 1980 eruption of Mount Saint Helens in Washington, Lassen Peak was the most recent volcanic outburst in the contiguous 48 states. The peak is the southernmost volcano in the Cascade Range, which extends from here into Canada. 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 spectacular glaciated canyons and is dotted and threaded by lakes and rushing clear streams. Snowbanks persist year-round and beautiful meadows are spread with wildflowers in spring. The eastern part of the park is a vast lava plateau more than one mile above sea level. Here are found small cinder cones (Fairfield Peak, Hat Mountain, and Crater Butte). 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). This forested, steep valley also has gorgeous large meadows. ...

Lassen geothermal area - Sulphur Works, Bumpass Hell (largest), Little Hot Springs Valley, Boiling Springs Lake, Devils Kitchen, and Terminal Geyser - offer bubbling mud pots, steaming fumaroles, and boiling water. Some of these thermal features are getting hotter. Scientists think that Lassen Park and Mount Shasta are the most likely candidates in the Cascades to join Mount Saint Helens as active volcanoes.

Bumpass Hell:

This is Lassen's most spectacular and diversified hydrothermal area, with hot springs, mudpots, fumaroles, and mud volcanoes.

Sulphur Works:

(This) hydrothermal area is the most accessible hot springs area in Lassen Volcanic National Park. It is thought to be part of the central vent system of ancient Mount Tehama ... A short paved trail leads to sputtering hot springs, steaming fumaroles and hot bubbling mudpots. ... Slippery clay and thin crusty coverings could lead to a dunking in 195 degree F (76 degrees C) water and mud. Most water in the thermal areas of the park contains sulphurous or sulphuric acid ... The odor is mainly that of hydrogen sulphide. Much of the white clay is tinted yellow, tan, or pink by minerals, chiefly iron oxides.

What is being done to monitor the Lassen volcanic center?

After the eruption of Mount St. Helens in 1980, the U.S. Geological Survey (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. 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.

Between 1980 and 1984, the U.S. Geological Survey's David A. Johnston Cascades Volcano Observatory (CVO) established baseline geodetic networks at Mount Baker, Mount Rainer, and Mount St. Helens in Washington, Mount Hood and Crater Lake in Oregon, and Mount Shasta and Lassen Peak in California. To this list of potentially active volcanoes, CVO extended its monitoring program in 1985 to include Newberry and South Sister volcanoes in central Oregon. The Newberry and South Sister networks were re-measured in 1986 and will be measured periodically in future years. Improvements since 1984 in the recording of endpoint and flightline temperatures resulted in better overall data than obtained previously. The improvements included: calibration of all the sensors and precision thermistors, installation of a new recording system for flightline data, and recording of endpoint temperatures 6 meters above ground level. The data collected in 1985 and 1986 indicate little or no apparent deformation at either volcano between surveys.

Mount Lassen Monitoring Menu

To the west and north of Susanville, the Lassen National Forest covers a mountainous region of 1.1 million acres. It is an area of great diversity whichaccommodatess much of the recreation available in the County. Fascinating geothermal activity can be seen in Lassen Volcanic National Park, which lies within the forest boundaries.

USFS Links

In May 1914 Lassen Peak burst into eruption, beginning a seven-year cycle of sporadic volcanic outbursts. The climax of the episode took place in 1915, when the peak blew an enormous mushroom cloud some seven miles into the stratosphere. The reawakening of this volcano, which began as a vent on a larger extinct volcano known as Tehama, profoundly altered the surrounding landscape.

The area was made a National Park in 1916 because of its significance as an active volcanic landscape. The park is a compact laboratory of volcanic phenomena and associated thermal features (except true geysers). It is part of a vast geographic unit - a great lava plateau with isolated volcanic peaks - that also encompasses Lava Beds National Monument (California) and Crater Lake National Park (Oregon).

The Lassen volcanic center is within the Lassen Volcanic National Park, approximately 65 miles east of Redding, California, or 240 kilometers west of Reno, Nevada. Access within the Park is by California Highway 89, which runs through the volcanic center.

Lassen Volcanic National Park

[Map,20K,InlinedGIF]
Lassen Volcanic National Park with Select Place Names
-- Modified from: National Park Service Map

Bumpass Hell

• self-guiding nature trail is a 2.2-mile walk to a hot spring basin. This is Lassen's most spectacular and diversified hydrothermal area, with hot springs, mudpots, fumaroles, and mud volcanoes. The walk through it is another 0.8 mile. -- Excerpt from: Schulz, Paul E., 1981 Revision, Road Guide to Lassen Volcanic National Park: Published in cooperation with the National Park Service, Copyright 1968 by the Loomis Museum Association.

Bumpass Mountain

• Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak are prominent domes. These have been extensively glaciated so that no trace of their original pumiceous carapace is preserved and their massively jointed, devitrified interiors are exposed. -- Excerpt from: Clynne, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219

Chaos Crags and Chaos Jumbles

• Three episodes of volcanism have occurred at the Lassen volcanic center in the past 1,100 years. These are the complex eruption at Chaos Crags, the eruptions at Cinder Cone, and the summit eruptions of Lassen Peak in 1914-1917. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219, Contribution by Michael A. Clynne

• The development of Chaos Crags forms a typical silicic volcanic cycle. The deposits originating from Chaos Crags indicate a complex eruption 1,100-1,000 years ago. Initial activity included formation of a tephra cone, emplacement of two pyroclastic flows, and growth of a dome that plugged the vent. After a quiet interval of approximately 70 years, the dome was destroyed by a violent eruption that emplaced a pyroclastic flow and an air-fall tephra lobe. These deposits are best seen in the drainages of Manzanita and Lost Creeks within 10 kilometers of the Chaos Crags. This violent eruption was followed by the growth of 5 domes, 3 of which had hot, dome-collapse avalanches. Chaos Jumbles formed 700 years later when one of the domes collapsed in a series of 3 cold rockfall-avalanches. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219, Contribution by Michael A. Clynne

• The surface morphology of the Chaos Crags domes is nearly unmodified by erosion processes. The Chaos Crags domes are steep-sided with extremely rough terrain on the top. The talus cones and piles around their bases are primary crumble breccia. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219, Contribution by Michael A. Clynne

• The 1980 eruption of Mount Saint Helens reduced Lassen's superlative status, but it increased the park's significance as an over 70-year laboratory of possible recovery patterns for Mount Saint Helens. The Devastated Area evidences the combined mud flow and gas blast destruction typical of many volcanic eruptions in the Cascades. The Chaos Jumbles area looks similarly destroyed, but for a different reason. An air-cushioned avalanche - one that fell so rapidly en masse that it trapped and compressed air beneath itself - crashed down the Chaos Crags about 300 years ago. The air acted as a lubricant, enabling the avalanche to rush across the valley at more than 100 miles per hour. It pushed 400 feet up the side of Table Mountain, before losing its momentum and surging back down across Manzanita Creek. -- Excerpt from: U.S. National Park Service, Lassen Volcano National Park Website, March 2002

Cinder Cone

• Three episodes of volcanism have occurred at the Lassen volcanic center in the past 1,100 years. These are the complex eruption at Chaos Crags, the eruptions at Cinder Cone, and the summit eruptions of Lassen Peak in 1914-1917. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219, Contribution by Michael A. Clynne

• The eruption of Cinder Cone is typical of mafic volcanism in the Lassen area. The Cinder Cone eruptive episode consists of 4 basaltic andesite lava flows, a complex vent cone, and an ash blanket covering 200-300 square kilometers. Two lava flows erupted before the ash blanket and two followed the ash blanket. All of these erupted over a short time interval of approximately 425 Carbon-14 years ago. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219, Contribution by Michael A. Clynne

• ... beautifully symmetrical Cinder Cone ... northeast of Lassen Peak ... elevation: 6,907 feet ... accessible from the Butte Lake Campground and Ranger Station, and the Nobles Emigrant Trail. -- Excerpt from: National Park Service, 1983, Lassen Volcanic National Park

• Cinder Cone in Lassen Volcanic National Park is a 700-foot-high volcanic cone. Its age has been controversial since the 1870's, when many people thought it was only a few decades old. Later, the cone and associated lava flows were thought to have formed about A.D. 1700 or during a 300-year-long series of eruptions ending in 1851. However, recent studies by U.S. Geological Survey (USGS) scientists, working in cooperation with the National Park Service to better understand volcanic hazards in the Lassen area, have firmly establised that Cinder Cone was formed in eruptions about 1650. -- Excerpt from: Clynne, et.al., 2000, How Old is "Cinder Cone"? -- Solving a Mystery in Lassen Volcanic National Park, California: USGS Fact Sheet 023-00

• Cinder Cone is a 700-foot-high cone of loose scoria. Scoria forms when blobs of gas-charged lava are thrown into the air during an eruption and cool in flight, falling as dark volcanic rock containing cavities created by trapped gas bubbles. The summit of Cinder Cone has a crater with a double rim, probably created by fluctuating eruptive activity late in its formation. The cone also has several associated blocky lava flows, and a realted, wide-spread ash deposit identifiable for 8 to 10 miles from the cone. -- Excerpt from: Clynne, et.al., 2000, How Old is "Cinder Cone"? -- Solving a Mystery in Lassen Volcanic National Park, California: USGS Fact Sheet 023-00

• There are actually two scoria cones at Cinder Cone -- the remnants of a nearly completely buried earlier cone can be seen on the large cone's south side. Much of the earlier cone was probably destroyed by lava flows erupting from its base. Blocks of red, cemented scoria within the Painted Dunes lava flows are pieces of this earlier cone, which were carried away by the flowing lava. -- Excerpt from: Clynne, et.al., 2000, How Old is "Cinder Cone"? -- Solving a Mystery in Lassen Volcanic National Park, California: USGS Fact Sheet 023-00

Crater Butte

• 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 spectacular glaciated canyons and is dotted and threaded by lakes and rushing clear streams. Snowbanks persist year-round and beautiful meadows are spread with wildflowers in spring. The eastern part of the park is a vast lava plateau more than one mile above sea level. Here are found small cinder cones (Fairfield Peak, Hat Mountain, and Crater Butte). Forested with pine and fir, this area is studded with small lakes, but it boasts few streams. -- Excerpt from: U.S. National Park Service, Lassen Volcanic National Park Website, March 2002

Devastated Area

• The Devastated Area evidences the combined mud flow and gas blast destruction typical of many volcanic eruptions in the Cascades. -- Excerpt from: U.S. National Park Service, Lassen Volcanic National Park Website, March 2002

Fairfield Peak

• 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 spectacular glaciated canyons and is dotted and threaded by lakes and rushing clear streams. Snowbanks persist year-round and beautiful meadows are spread with wildflowers in spring. The eastern part of the park is a vast lava plateau more than one mile above sea level. Here are found small cinder cones (Fairfield Peak, Hat Mountain, and Crater Butte). Forested with pine and fir, this area is studded with small lakes, but it boasts few streams. -- Excerpt from: U.S. National Park Service, Lassen Volcanic National Park Website, March 2002

Hat Mountain

• 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 spectacular glaciated canyons and is dotted and threaded by lakes and rushing clear streams. Snowbanks persist year-round and beautiful meadows are spread with wildflowers in spring. The eastern part of the park is a vast lava plateau more than one mile above sea level. Here are found small cinder cones (Fairfield Peak, Hat Mountain, and Crater Butte). Forested with pine and fir, this area is studded with small lakes, but it boasts few streams. -- Excerpt from: U.S. National Park Service, Lassen Volcanic National Park Website, March 2002

Hot Rock

• The large rock ... is a piece of the lava dome that filled Lassen's summit crater during the week before the May 19 eruption and was carried to its present location by the avalanche caused by this eruption. Today, this rock can be seen on the Devastated Area Interpretive Trail. -- Excerpt from: Clynne, et.al., 1999, Eruptions of Lassen Peak, California, 1914 to 1917: USGS Fact Sheet 173-98

• [Image, 47K,JPG]
  "Hotrock" and Mount Lassen, 1915 and 1984 -- 1915 photo courtesy Lassen Volcanic National Park, by B.F. Loomis, and 1984 Photo by Lyn Topinka, USGS/CVO

Lassen Peak Lava Dome

• Lassen Peak began as a volcanic vent on Mount Tehama's northern flank. Considered the world's largest plug dome volcano, it rises 2,000 feet to an elevation of 10,457 feet. -- Excerpt from: U.S. National Park Service Website, Geology Fieldnotes - Lassen Volcanic National Park, California, April 2000

• Lassen Peak is the largest of a group of more than 30 volcanic domes erupted over the past 300,000 years in Lassen Volcanic National Park in northern California. These mound-shaped accumulations of volcanic rock, called lava domes, were created by eruptions of lava too viscous to readily flow away from its source. Eruptions about 27,000 years ago formed Lassen Peak, probably within only a few years. With a height of 2,000 feet and a volume of half a cubic mile, it is one of the largest lava domes on Earth. -- Excerpt from: Clynne, et.al., 1999, Eruptions of Lassen Peak, California, 1914 to 1917: USGS Fact Sheet 173-98

• When Lassen Peak formed, it looked much like the nearby 1,100-year-old Chaos Crags Domes, with steep sides covered with angular rock talus. However, from 25,000 to 18,000 years ago, during the last ice age, Lassen's shape was significantly altered by glacial erosion. For example, the bowl-shaped depression on the volcano's northeastern flank, called a circue, was eroded by a glacier that extended out 7 miles from the dome. -- Excerpt from: Clynne, et.al., 1999, Eruptions of Lassen Peak, California, 1914 to 1917: USGS Fact Sheet 173-98

• The second and third sequences of lavas at the Lassen volcanic center comprise the dacite dome field. The second sequence erupted from 250,000-200,000 years ago ... The third sequence consists of porphyritic hornblende-biotite rhyodacite erupted as lava domes, short thick lava flows, and pyroclastic flows erupted in at least 12 episodes during the past 100,000 years. Rocks of this sequence form the northern and western portions of the dacite dome field, and their vents are concentrated in linear chains near the inferred western edge of the old caldera. The most prominent features of this sequence are Eagle Peak (55,000 years ago), Sunflower Flat domes (35,000 years ago), Lassen Peak (approximately 25,000 years ago), and Chaos Crags (1,050 years ago). -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219, Contribution by Michael A. Clynne

Mount Helen

• Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak are prominent domes. These have been extensively glaciated so that no trace of their original pumiceous carapace is preserved and their massively jointed, devitrified interiors are exposed. -- Excerpt from: Clynne, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219

Reading Peak

• Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak are prominent domes. These have been extensively glaciated so that no trace of their original pumiceous carapace is preserved and their massively jointed, devitrified interiors are exposed. -- Excerpt from: Clynne, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219

Ski Heil Peak

• Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak are prominent domes. These have been extensively glaciated so that no trace of their original pumiceous carapace is preserved and their massively jointed, devitrified interiors are exposed. -- Excerpt from: Clynne, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.216-219

Sulphur Works

• ... hydrothermal area is the most accessible hot springs area in Lassen Volcanic National Park. It is thought to be part of the central vent system of ancient Mount Tehama ... A short paved trail leads to sputtering hot springs, steaming fumaroles and hot bubbling mudpots. ... Slippery clay and thin crusty coverings could lead to a dunking in 195 degree F (76 degrees C) water and mud. Most water in the thermal areas of the park contains sulphurous or sulphuric acid ... The odor is mainly that of hydrogen sulphide. Much of the white clay is tinted yellow, tan, or pink by minerals, chiefly iron oxides. -- Excerpt from: Schulz, Paul E., 1981 Revision, Road Guide to Lassen Volcanic National Park: Published in cooperation with the National Park Service, Copyright 1968 by the Loomis Museum Association.

• The name Sulphur Works was first used in 1865, when efforts were made by T. M. Boarman and Dr. Milton Supan to develop the sulphur and clay potential of the area. This land was filed upon originally as a mining claim, but was actively used only for the tourist trade beginning about 1940. some of the acidic thermal water was used for hot baths. The property was acquired by the National Park Service in 1951. -- Excerpt from: Schulz, Paul E., 1981 Revision, Road Guide to Lassen Volcanic National Park: Published in cooperation with the National Park Service, Copyright 1968 by the Loomis Museum Association.

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