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16 Cards in this Set
- Front
- Back
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volcanic dome
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a volcanic dome is characterized by an upheaved, plug-like conduit filling that forms when viscous lava is forced through a vent onto the earth’s surface. Like toothpaste squeezed out of a tube, the viscous lava is unable to flow freely, so it builds a bulbous dome over its vent.
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What kind of volcano was Tehama (Brokeoff Volcano) in Lassen Volcanic National Park?
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Composite volcano (also known as a stratovolcano)
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During what epoch did Tehama form?
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Pleistocene is when Tehama collapsed
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What eventually happened to Tehama?
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It collapsed, forming a caldera.
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What geologic features now mark the location where it once stood?
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The Lassen Dome
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Lassen Peak in Lassen Volcanic National Park is composed of what type of volcanic rock.
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Dacite
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Describe how Lassen Peak formed.
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About 18,000 years ago, the volcanic dome that became Lassen Peak began pushing up through a vent in the pre-collapse dacite flows.
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What is the relationship between the formation of this volcano and the type of rock comprising it?
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Dacite is intermediate in composition between rhyolite and andesite. Because dacide has a higher percentage of silica than andesite, it tends to flow less easily, hence its propensity for constructing domes.
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Did Lassen Peak form slowly or quickly?
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Remarkably short time
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How is Lassen Peak related tectonically to the other large volcanoes in the Cascade Range? How are the construction and composition of these other Cascade volcanoes very different from Lassen Peak?
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According to the plate tectonic theory, a spreading center, lying some 3000 miles offshore from northern California, Oregon, and Washington, adds about an inch of new crust each year to small plate of oceanic crust, thus moving it toward the pacific northwest coast. As this small plate collides with the westward moving north American plate, the denser oceanic crust bends down and slips beneath the leading edge of the continental plate.
The cascade volcanoes are products of the subduction of oceanic crust and marine sedimentary rocks |
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Bumpass Hell
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16 acre tract of boiling springs, steaming sulfur vapors, and bubbling mud pots that are associated with old caldera fissures.
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Chaos Crags
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Volcanic domes made up of several dacite plugs but has no crater
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Chaos Jumbles
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A rock avalanche that extends toward the northwest corner of the park from the base of Chaos Crags, was set off by explosion and partial collapse of one of the chaos crags domes about 300 years ago.
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the Devastated Area
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the tract of greatest destruction; a wide swath about 4 miles long, which marks the path of the mud and ash flows that roared down the mountain during the eruptions; scars are covered by natural reforestation but the trees are sparse and stunted due to the lack of nutrients for the soil
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Devils Kitchen
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hot sulfurous springs; strongly acidic so that holes and pits have been eaten into the bedrock.
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List at least three ways that lake basins (the low areas occupied by lakes) have formed in Lassen Volcanic National Park.
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Mudflow associated with eruptions, lake dammed by moraines, small valley glaciers that persisted at high elevations and in protected locations to form lakes
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