1. Volcanoes Chapter 6

2. Eruptions
Volcano – (#34) opening in Earth’s surface which allows gas & magma to escape
Magma: (#35) molten rock underground
Lava: (#36) molten rock at Earth’s surface
Two types
Non-explosive
calm flows of lava such as Mt. Kiluea or sea floor spreading
most common
happen over long periods, all the time
Explosive
clouds of hot ash, debris, and gas shoot out
rarer
sudden and destructive

3. Volcano Parts

4. Magma Explosiveness of eruption depends on:
water
silica in magma
gases
Water and CO2 remain dissolved in magma until pressure released
Like a can of soda exploding when top opened
Magma with high silica content very stiff and can plug vent opening
Builds pressure by preventing water and other gases from escaping

5. Eruption Materials Lava (non explosive) – liquid rock
Aa or blocky: high viscosity, stiff, slow moving, brittle, jagged or blocks
Pahoehoe or pillow lava: low viscosity, more fluid, faster moving, smooth

6. More Eruption Materials
Pyroclastic material (explosive) – magma hardens in the air or shatters existing rock
volcanic bombs
volcanic blocks
lapilli
volcanic ash
Pyroclastic flows (#37)
hot ash, dust, and gases ejected and flow rapidly downhill

7. Effects Deaths by blast or pyroclastic flows Ecologically damage
Climate change
ash in upper atmosphere
blocks sunlight
Mt. Tambora in Indonesia in 1815
12,000 direct deaths
80,000 deaths from hunger and disease
Food shortages in Europe and N. America next year due to reduced sunlight and temperature
Global temperatures dropped .5 degrees C

8. Types Shield Cinder cone Composite (aka stratovolcano)
(#39) Repeated lava flows build up over time from non-explosive eruptions
Gently sloping over wide area
Mauna Kea in Hawaii
Cinder cone
(#40) Pyroclastic material builds up from moderately explosive eruptions
Steep slopes of cinder cones
Not very stable, sometimes on sides of other volcanoes
Paricutin in Mexico
Composite (aka stratovolcano)
Most common type
(#41) Alternating flows of lava and pyroclastic material build up
Broad bases that get steeper towards top
Mt Fuji in Japan, Mt Hood, Mt Ranier, Mt St Helens, Mt Shasta

10. Other Volcanic Landforms
Craters
Calderas (#38)
Lava plateaus

11. Locations Divergent boundary – mid ocean ridges
most volcanic activity on Earth
Convergent boundary – subduction zones
descending oceanic crust
melting rock less dense and rises up
80% of all land volcanoes at convergent
Hot spots
mantle plumes far from plate boundaries
Hawaiian islands
Yellowstone