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) be modified by surrounding rock; and c) mix with other magma to produce different types of lavas seen at the surface.
Magma chamber at depth under Shasta; basaltic lava rises from the mantle below.

6. 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

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 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

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 eruptions from Medicine Lake volcano
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 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

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