Volcano Eruption Types: Quiet or Explosive
Depends on MAGMA CHARACTERISTICS
- How much silica is in the rock?
- How much water?
- What temperature does the rock melt?
Magma Composition and Characteristics
Granitic
Ocean Crust Melt
(Mafic Magmas)
Continental Crust Melt
(Felsic Magmas)
Eruption Types:
Quiet =
• Low silica content
• High water content
• High temp. magma
(deep mantle source)
• Low viscosity (runny,
low silica)
• Runny/Liquidy Lava
Hawaiian Hotspot Volcanoes: Hot spot
volcanoes are made from Deep Magma
Plumes from the Mantle. This is hot, low silica
rock from deep in the mantle!
Pahoehoe
A’a
Explosive Eruptions:
• High-silica content
(continental crust melt)
• Low temp. magma
• High viscosity
• High gas content
• PYROCLASTIC – gas, ash,
superheated rock fragments.
Subduction/Ring of Fire Volcanoes:
Subduction volcanoes are made from melting
rocks of the CRUST. Crustal rock is high in
silica. Magma is cool because it is formed in
the crust (not deep in the mantle).
Mount St. Helens, WA
“pyroclastic”
Eruption Types
Mount St. Helens, WA
Pre 1980
eruption
Today
Post 1980
eruption
Yellowstone is over a hot spot where magma from the mantle is rising and
melting the crust above. This magma heat water for hot springs and geysers.
There are no volcanoes there now, but have been in the past. A Yellowstone
volcano would be formed by melting a lot of continental crust. This would
make silica rich magmas that are EXPLOSIVE.
Volcano Hazards: Why
are volcanoes Least Hazard
dangerous?
Great Hazard
1. Lava flows (burns/
fire)
2. Ash (buries,
suffocates)
3. Pyroclastic flows
(gas, ash,
superheated rock
fragments
<bombs>)
4. Mudflows/Lahars
5. Acidification of
water
6. Climate
change/mass
extinction
Lahar: Volcanic landslide/mudslide
Eruptions and Eqs that accompany them trigger landslides;
Lava melts snow at the top of the volcano  Mudslide
Very Hazardous  wipe out villages/ fatalities