Shasta/Lava Beds/Lassen

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Shasta/Lava Beds/Lassen

description

Shasta/Lava Beds/Lassen. The Cascade Volcanoes. Caused by subduction Explorer, Juan de Fuca, and Gorda = oceanic plates North American = continental plate. Mt. Shasta. prominent landmark at an elevation of 4,317 meters (14,162 feet) - PowerPoint PPT Presentation

Transcript of Shasta/Lava Beds/Lassen

Page 1: Shasta/Lava Beds/Lassen

Shasta/Lava Beds/Lassen

Page 2: Shasta/Lava Beds/Lassen

The Cascade Volcanoes

• Caused by subduction

• Explorer, Juan de Fuca, and Gorda = oceanic plates

• North American = continental plate

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Mt. Shasta• prominent landmark at an elevation of 4,317

meters (14,162 feet) • volume of nearly 500 cubic kilometers makes it

the largest of the Cascade stratovolcanoes• Most recent eruption occurred 200 years ago• 7 main glaciers recognized on Shasta today• Seismically and geothermally active

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Rocks and Minerals

• RocksBasaltAndesite Dacite

• MineralsOlivene

HyperstheneAugite

Hornblende Biotite

PlagioclaseQuartzMagnetite

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Why are Lavas Diverse?

Magma chamber at depth underShasta; basaltic lava rises fromthe mantle below.

Magma can: a) differentiate; b) bemodified by surrounding rock; and c) mix with other magma to producedifferent types of lavas seen at thesurface.

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Glaciers and Glacial Erosion

• 7 main glaciers on Shasta

• Total volume of ice isabout 140 million cubic meters

• Cirques, aretes, and moraines are all seenon Shasta

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Streams and Debris Flows• Multiple debris flows have happened

during historic time and will continue to occur

• As water runs off of the slopes it maybecome 2 times as dense as water whenvolcanic sediment is incorporated

• Slurries develop that are similar to concrete

• Streams are able to buoy up and carry rocksmuch larger than normal

• http://www.siskiyous.edu/Shasta/map/mp/wdf8-97.mpg

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Mass Movement

• Downslope falls, slides, or flows of weathered rock due to gravity

• 3 factors = steep slopes, weak rocks, and water

• Rockfalls common• Debris flows common• Debris Avalanches

uncommon, but do occur on Shasta

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Lava Beds National Monument

• Formed from eruptionsfrom Medicine Lakevolcano

• Main rock types = Basalt

Aa andPahoehoe

AndesiteRhyoliteTuffObsidianPumice

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Volcanic Features• Lava Tube Caves

• Cinder Cones

• Spatter Cones

• Craters

• Fault Scarps

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Lassen PeakNational Volcanic Park

• Formed from a massiveextrusion of dacite ~11,000 years ago

• May have only erupted for a year or two

• Mt. Maidu, Mt. Tehama, and Thousand Lakes volcano also formed landscape in greater area

• Glaciers have played a major role in shaping the landscape around Lassen

• Geothermal activity continues to date

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Volcanic & Geothermal Features

• Plug domes• Cinder cones• Craters• Debris Avalanches• Lava Flows• Hot springs• Fumaroles• Boiling mud pots

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Conclusion

• Whole region is formed by subduction• Some lavas are silica rich – pasty, sticky,

explosive (Mt. Shasta, Lassen Peak)• Some lavas are silica poor – runny, less

explosive/effusive (Medicine Lake/Lava Beds)• Glaciers have played a major role in shaping the

landscape• Geologic hazards (mass movements, eruptions)

continue to affect the region