Mount Tehama
Encyclopedia
Mount Tehama is an eroded andesitic
stratovolcano
in the Cascade Volcanic Arc
and the Cascade Range
in Northern California
. Part of the Lassen volcanic center, its highest remaining remnant, Brokeoff Mountain, is itself the second highest peak in Lassen Volcanic National Park
and connects to the park's highest point, Lassen Peak
. Located on the border of Tehama County
and Shasta County
, Tehama's peak is the highest point in the former. The hikers that summit this mountain each year are treated to "exceptional" views of Lassen Peak, the Central Valley of California, and many of the park's other features. On clear days, Mount Shasta
can also be seen in the distance.
Tehama started life some 600,000 years ago. At its peak, it reached approximately 3,350 meters (11,000 ft) high, with a diameter at the base of approximately 12 kilometers. Volcanic activity then declined 400,000 years ago, with other volcanic lava dome
s forming at the edges of Mount Tehama later on, the largest and best known of which is Lassen Peak. A combination of continued hydrothermal activity and erosion
, particularly by glacier
s during ice age
s, removed the central cone of the volcano, leaving a large caldera
, the northern edge of which can still be seen.
Other remnants of Mount Tehama include Mount Conard, Pilot Pinnacle, Mount Diller, and Diamond Peak.
which cut through the Lassen Peak vicinity near Sacramento Valley
. One of the main landmarks along this trail was a volcano. Called Lassen Peak
after Peter Lassen, a prominent blacksmith and guide who escorted California settlers, the volcano and the area around it were given merit for their gripping volcanic phenomena, which included lava beds and extinct volcanic cones. In May 1907, Lassen Peak was declared a National Monument by President Theodore Roosevelt
to protect the area for "future generations to study and enjoy". Roosevelt had been told that the area was actually extinct in terms of eruptive activity. Despite assurance from Native Americans in the area that the mountain was indeed active, settlers continued to think that Lassen Peak was extinct and "dead" and so continued to settle nearby. The natives continued to declare that "one day the mountain would blow itself to pieces". In May 1914, almost exactly seven years later, the volcano began a large explosive eruption sequence. More than a hundred eruptions of varying size took place over the next seven years, attracting national interest and the designation of national park
in 1916.
, an area of highly active tectonic activity that includes seismicity and volcanism. Tehama and the other volcanoes near Lassen Peak were produced by subduction
of the oceanic Pacific Plate
under the North American Plate
.
Mount Tehama originated in the Lassen volcanic complex, an area of active volcanism for more than three million years. It formed during a period of eruptive activity approximately 600,000 years ago on a series of faults; the largest of these eruptions was about 50 times as powerful as the 1980 eruption of Mount St. Helens
. During the Pleistocene
, constantly renewed lava of andesite
flowed from the caldera of the volcano, eventually becoming "interbedded" and heightening the mountain. By the time it reached its peak size, the volcano was immense, measuring at its base between 11 miles (18 km) and 15 miles (24 km) wide and more than 11000 feet (3,353 m) tall. Activity at Tehama lasted for approximately 200,000 years. Eruptions varied from ejection of pyroclastic material to andesitic
lava flows built of olivine
and other minerals.
Soon after the formation of Tehama, other, smaller volcanoes began to form. Shield volcano
es like Raker Peak, Red Mountain, Prospect Peak, and Mount Harkness appeared. At this point, the Pleistocene
was coming to an end. One additional and final vent formed on the northeastern flank of the volcano, erupting glassy dacitic flows. Over time, the volcano became dilapidated from extensive erosion and "hydrothermal activity", and collapsed. Prior leaking of dacite dried, forming smaller landforms like Mount Conard and Diamond Peak. The result of this huge collapse was a caldera
2 miles (3 km) in diameter. Later activity built more than thirty other cones known as the Lassen Domes. Today the most active volcano in the area is Lassen Peak
. Other smaller craters younger than 50,000 years are also active.
Tehama's remains sit under Mount Lassen in Shasta County, California. Sulphur Works, an area known for its sharp, putrid scent, is thought to be the center of the old caldera. It is located by Diamond Point, the conduit for magmas in Tehama.
After Tehama disappeared, local volcanism became more silicic
, moving to Lassen Peak's northern flank. The last 400,000 years have seen at least three known flows, parts of which are still on Raker Peak and Mount Conard. A subsequent explosive eruption ejected 12 cubic miles (50 km³) of material and created a large crater, which was soon covered by lava. Twelve lava dome
s were built throughout the area and the next period of eruptive activity began. Spanning 50,000 years it ejected 3.5 cubic miles (15 km³) to 6 cubic miles (25 km³) of material and was followed by a third period. At least twelve periods of activity have taken place since Tehama formed, consisting of activity including pyroclastic flows, pasty lavas, and additional lava domes. Among the vents built by this activity include Lassen Peak.
thickets are present, as well as incense cedar, red fir
s, and western white pine
. At higher elevations, groups of mountain hemlock
and lupin
es prevail. Eagle
s and hawk
s can be frequently noted on high crags, and squirrel
s and pika
live about the mountain.
Due to the characteristically intermittent eruptions of active volcanoes such as Lassen Peak, there is some threat from the volcanoes of the LVNP. Dacitic
explosive eruption
s have taken place within the last 50,000 years at Lassen Peak, Chaos Crags
, and Sunflower Flat, and effusive eruption
s of basalt have occurred at Tumble Buttes, Hat Mountain, and Prospect Peak. Pyroclastic flow
s and lahar
s could easily occur near glaciated areas and in river valleys like Hat Creek Valley. In addition to the volcanic hazards that could possibly occur, one volcano did erupt in the 20th century (Lassen Peak
).
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
in the Cascade Volcanic Arc
Cascade Volcanoes
The Cascade Volcanoes are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 mi ...
and the Cascade Range
Cascade Range
The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...
in Northern California
Northern California
Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...
. Part of the Lassen volcanic center, its highest remaining remnant, Brokeoff Mountain, is itself the second highest peak in Lassen Volcanic National Park
Lassen Volcanic National Park
Lassen Volcanic National Park is a United States National Park in northeastern 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...
and connects to the park's highest point, Lassen Peak
Lassen Peak
Lassen Peak is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia...
. Located on the border of Tehama County
Tehama County, California
Tehama County is a county located in the northern part of the U.S. state of California. It is bisected by the Sacramento River. As of 2010 its population was 63,463, up from 56,039 as of 2000. The county seat is Red Bluff.-History:...
and Shasta County
Shasta County, California
Shasta County is a county located in the northern portion of the U.S. state of California. The county occupies the northern reaches of the Sacramento Valley, with portions extending into the southern reaches of the Cascade Range. As of the 2010 census, the population was 177,223, up from 163,256...
, Tehama's peak is the highest point in the former. The hikers that summit this mountain each year are treated to "exceptional" views of Lassen Peak, the Central Valley of California, and many of the park's other features. On clear days, Mount Shasta
Mount Shasta
Mount Shasta is located at the southern end of the Cascade Range in Siskiyou County, California and at is the second highest peak in the Cascades and the fifth highest in California...
can also be seen in the distance.
Tehama started life some 600,000 years ago. At its peak, it reached approximately 3,350 meters (11,000 ft) high, with a diameter at the base of approximately 12 kilometers. Volcanic activity then declined 400,000 years ago, with other volcanic lava dome
Lava dome
|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...
s forming at the edges of Mount Tehama later on, the largest and best known of which is Lassen Peak. A combination of continued hydrothermal activity and erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
, particularly by glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s during ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
s, removed the central cone of the volcano, leaving a large caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
, the northern edge of which can still be seen.
Other remnants of Mount Tehama include Mount Conard, Pilot Pinnacle, Mount Diller, and Diamond Peak.
History
The area near Lassen Peak became a haven for new settlers throughout the 1800s. Wagon trains followed winding trails on the Nobles Emigrant TrailNobles Emigrant Trail
The Nobles Emigrant Trail, also known as the Fort Kearney, South Pass and Honey Lake Wagon Road, is a trail in California that was used by emigrant parties from the east as a shortened route to northern California. It was pioneered in 1851 by William Nobes, who discovered an easy shortcut between...
which cut through the Lassen Peak vicinity near Sacramento Valley
Sacramento Valley
The Sacramento Valley is the portion of the California Central Valley that lies to the north of the San Joaquin-Sacramento Delta in the U.S. state of California. It encompasses all or parts of ten counties.-Geography:...
. One of the main landmarks along this trail was a volcano. Called Lassen Peak
Lassen Peak
Lassen Peak is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia...
after Peter Lassen, a prominent blacksmith and guide who escorted California settlers, the volcano and the area around it were given merit for their gripping volcanic phenomena, which included lava beds and extinct volcanic cones. In May 1907, Lassen Peak was declared a National Monument by President Theodore Roosevelt
Theodore Roosevelt
Theodore "Teddy" Roosevelt was the 26th President of the United States . He is noted for his exuberant personality, range of interests and achievements, and his leadership of the Progressive Movement, as well as his "cowboy" persona and robust masculinity...
to protect the area for "future generations to study and enjoy". Roosevelt had been told that the area was actually extinct in terms of eruptive activity. Despite assurance from Native Americans in the area that the mountain was indeed active, settlers continued to think that Lassen Peak was extinct and "dead" and so continued to settle nearby. The natives continued to declare that "one day the mountain would blow itself to pieces". In May 1914, almost exactly seven years later, the volcano began a large explosive eruption sequence. More than a hundred eruptions of varying size took place over the next seven years, attracting national interest and the designation of national park
Lassen Volcanic National Park
Lassen Volcanic National Park is a United States National Park in northeastern 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...
in 1916.
Geography and geology
The state of California is located on the Pacific Ring of FirePacific Ring of Fire
The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements...
, an area of highly active tectonic activity that includes seismicity and volcanism. Tehama and the other volcanoes near Lassen Peak were produced by subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
of the oceanic Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
under the North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...
.
Mount Tehama originated in the Lassen volcanic complex, an area of active volcanism for more than three million years. It formed during a period of eruptive activity approximately 600,000 years ago on a series of faults; the largest of these eruptions was about 50 times as powerful as the 1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
The 1980 eruption of Mount St. Helens, a stratovolcano located in Washington state, in the United States, was a major volcanic eruption. The eruption was the only significant one to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California...
. During the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
, constantly renewed lava of andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
flowed from the caldera of the volcano, eventually becoming "interbedded" and heightening the mountain. By the time it reached its peak size, the volcano was immense, measuring at its base between 11 miles (18 km) and 15 miles (24 km) wide and more than 11000 feet (3,353 m) tall. Activity at Tehama lasted for approximately 200,000 years. Eruptions varied from ejection of pyroclastic material to andesitic
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
lava flows built of olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
and other minerals.
Soon after the formation of Tehama, other, smaller volcanoes began to form. Shield volcano
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
es like Raker Peak, Red Mountain, Prospect Peak, and Mount Harkness appeared. At this point, the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
was coming to an end. One additional and final vent formed on the northeastern flank of the volcano, erupting glassy dacitic flows. Over time, the volcano became dilapidated from extensive erosion and "hydrothermal activity", and collapsed. Prior leaking of dacite dried, forming smaller landforms like Mount Conard and Diamond Peak. The result of this huge collapse was a caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
2 miles (3 km) in diameter. Later activity built more than thirty other cones known as the Lassen Domes. Today the most active volcano in the area is Lassen Peak
Lassen Peak
Lassen Peak is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia...
. Other smaller craters younger than 50,000 years are also active.
Tehama's remains sit under Mount Lassen in Shasta County, California. Sulphur Works, an area known for its sharp, putrid scent, is thought to be the center of the old caldera. It is located by Diamond Point, the conduit for magmas in Tehama.
After Tehama disappeared, local volcanism became more silicic
Silicic
Silicic is a term used to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually put at at least 65 percent. Granite and rhyolite are typical silicic rocks....
, moving to Lassen Peak's northern flank. The last 400,000 years have seen at least three known flows, parts of which are still on Raker Peak and Mount Conard. A subsequent explosive eruption ejected 12 cubic miles (50 km³) of material and created a large crater, which was soon covered by lava. Twelve lava dome
Lava dome
|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...
s were built throughout the area and the next period of eruptive activity began. Spanning 50,000 years it ejected 3.5 cubic miles (15 km³) to 6 cubic miles (25 km³) of material and was followed by a third period. At least twelve periods of activity have taken place since Tehama formed, consisting of activity including pyroclastic flows, pasty lavas, and additional lava domes. Among the vents built by this activity include Lassen Peak.
Flora and fauna
Near the trailhead at lower elevations, alderAlder
Alder is the common name of a genus of flowering plants belonging to the birch family . The genus comprises about 30 species of monoecious trees and shrubs, few reaching large size, distributed throughout the North Temperate Zone and in the Americas along the Andes southwards to...
thickets are present, as well as incense cedar, red fir
Red Fir
Abies magnifica, the Red Fir or Silvertip fir, is a western North American fir, native to the mountains of southwest Oregon and California in the United States. It is a high altitude tree, typically occurring at altitude, though only rarely reaching tree line...
s, and western white pine
Western White Pine
Western White Pine, Pinus monticola in the family Pinaceae, is a species of pine that occurs in the mountains of the western United States and Canada, specifically the Sierra Nevada, the Cascade Range, the Coast Range, and the northern Rocky Mountains. The tree extends down to sea level in many...
. At higher elevations, groups of mountain hemlock
Mountain Hemlock
Tsuga mertensiana, known as Mountain Hemlock, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Tulare County, California....
and lupin
Lupin
Lupinus, commonly known as Lupins or lupines , is a genus in the legume family . The genus comprises about 280 species , with major centers of diversity in South and western North America , and the Andes and secondary centers in the Mediterranean region and Africa Lupinus, commonly known as Lupins...
es prevail. Eagle
Eagle
Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...
s and hawk
Hawk
The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...
s can be frequently noted on high crags, and squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
s and pika
Pika
The pika is a small mammal, with short limbs, rounded ears, and short tail. The name pika is used for any member of the Ochotonidae, a family within the order of lagomorphs, which also includes the Leporidae . One genus, Ochotona, is recognised within the family, and it includes 30 species...
live about the mountain.
Recreation
Hiking is especially popular on the mountain during summer. The trip lasts between four and six hours, spans 7.4 miles (12 km), and offers "exceptional" views of Mount Diller, Lassen Peak, Chaos Crags, and Mount Conard.Due to the characteristically intermittent eruptions of active volcanoes such as Lassen Peak, there is some threat from the volcanoes of the LVNP. Dacitic
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
explosive eruption
Explosive eruption
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the...
s have taken place within the last 50,000 years at Lassen Peak, Chaos Crags
Chaos Crags
Chaos Crags is the youngest group of lava domes in Lassen Volcanic National Park, California, having been formed as five dacite domes 1,100-1,000 years ago...
, and Sunflower Flat, and effusive eruption
Effusive eruption
An effusive eruption is a volcanic eruption characterized by the outpouring of lava onto the ground...
s of basalt have occurred at Tumble Buttes, Hat Mountain, and Prospect Peak. Pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
s and lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
s could easily occur near glaciated areas and in river valleys like Hat Creek Valley. In addition to the volcanic hazards that could possibly occur, one volcano did erupt in the 20th century (Lassen Peak
Lassen Peak
Lassen Peak is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia...
).