Transcript 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)
• 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
Rocks and Minerals
• Rocks
Basalt
Andesite
Dacite
• Minerals
Olivene
Hypersthene
Augite
Hornblende
Biotite
Plagioclase
Quartz
Magnetite
Why are Lavas Diverse?
Magma chamber at depth under
Shasta; basaltic lava rises from
the mantle below.
Magma can: a) differentiate; b) be
modified by surrounding rock; and
c) mix with other magma to produce
different types of lavas seen at the
surface.
Glaciers and Glacial Erosion
• 7 main glaciers on Shasta
• Total volume of ice is
about 140 million cubic
meters
• Cirques, aretes, and
moraines are all seen
on Shasta
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 may
become 2 times as dense as water when
volcanic sediment is incorporated
• Slurries develop that are similar to concrete
• Streams are able to buoy up and carry rocks
much larger than normal
• http://www.siskiyous.edu/Shasta/map/mp/wdf8-97.mpg
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
Lava Beds National Monument
• Formed from eruptions
from Medicine Lake
volcano
• Main rock types =
Basalt
Aa and
Pahoehoe
Andesite
Rhyolite
Tuff
Obsidian
Pumice
Volcanic Features
• Lava Tube Caves
• Cinder Cones
• Spatter Cones
• Craters
• Fault Scarps
Lassen Peak
National Volcanic Park
• Formed from a massive
extrusion 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
Volcanic & Geothermal Features
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Plug domes
Cinder cones
Craters
Debris Avalanches
Lava Flows
Hot springs
Fumaroles
Boiling mud pots
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