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Shasta/Lava Beds/Lassen

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)

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Shasta/Lava Beds/Lassen

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  1. Shasta/Lava Beds/Lassen

  2. The Cascade Volcanoes • Caused by subduction • Explorer, Juan de Fuca, and Gorda = oceanic plates • North American = continental plate

  3. 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

  4. Rocks and Minerals • Rocks Basalt Andesite Dacite • Minerals Olivene Hypersthene Augite Hornblende Biotite Plagioclase Quartz Magnetite

  5. Why are Lavas Diverse? Magma can: a) differentiate; b) bemodified by surrounding rock; and c) mix with other magma to producedifferent types of lavas seen at thesurface. Magma chamber at depth underShasta; basaltic lava rises fromthe mantle below.

  6. 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

  7. 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

  8. 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

  9. Lava Beds National Monument • Formed from eruptionsfrom Medicine Lakevolcano • Main rock types = Basalt Aa and Pahoehoe Andesite Rhyolite Tuff Obsidian Pumice

  10. Volcanic Features • Lava Tube Caves • Cinder Cones • Spatter Cones • Craters • Fault Scarps

  11. 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

  12. Volcanic & Geothermal Features • Plug domes • Cinder cones • Craters • Debris Avalanches • Lava Flows • Hot springs • Fumaroles • Boiling mud pots

  13. 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

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