ShastaLava BedsLassen

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 Pu
  mice

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