America's Volcanic Past
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| "Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994 |
MORE America's Volcanic Past - California
Volcanic Highlights and Features:
| [NOTE: This list is just a sample of various Lassen features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of the Lassen Region.] |
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.
Excerpt from: Clynne, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p. |
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| Lassen - Brief Volcanic History |
Ancestral Mount Tehama:1
About 600,000 years ago a great Pacific Ring of Fire stratovolcano
(Mount Tehama) gradually built up here through countless
eruptions. 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 Conard. Connect these
peaks in a circle to envision Mount Tehama's base - more than 11 miles wide.
Lassen Peak Plug Dome:1
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. The park's lava came from many vents.
Lassen Peak's Latest Eruption:1
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.
| Lassen Volcanic National Park |
Lassen Volcanic National Park:1
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 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).
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.
| Lassen Volcanic National Park - Places |
Bumpass Mountain:3
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.
Chaos Crags and Chaos Jumbles:1
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.
Development of Chaos Crags:3
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.
Cinder Cone:1
Recent geological evidence indicates that
Cinder Cone, also a volcano, erupted in the 18th century.
Crater Butte:1
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.
Devastated Area:1
The Devastated Area evidences the
combined mud flow and gas blast destruction typical of many volcanic eruptions in the Cascades.
Fairfield Peak:1
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.
Hat Mountain:1
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.
Hot Rock2
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.
|
Lassen Peak Plug Dome:1
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. The park's lava came from many vents.
Mount Helen:3
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.
Reading Peak:3
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.
Ski Heil Peak:3
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.
Sulphur Works:4
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.
| America's Volcanic Past - California |
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