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*information presented comes from Earth Science published by Glencoe McGraw-Hill
All volcanoes are fueled by magma
1. Magma forms deep within the Earth when temperatures are high enough (800C to 1200C) to melt rock
Besides temperature, pressure and presence of water contribute to the melting of rocks
b. a wet rock will melt at a lower temperature than the same rock when dry, regardless of pressure
2. Types of magma
Oceanic crust and oceanic sediments
3. Viscosity: the internal resistance to flow. The higher the viscosity, the slower the lava flow.
Anatomy of a volcano
1. Lava: magma once it reaches the earth's surface
2. Vent: opening in the crust where lava erupts
3. Crater: a bowl-shaped depression at the top of a volcano around the vent
4. Calderas: A depression much larger than a crater; forms when the top or side of a volcano collapses into the magma chamber
B. Types of Volcanoes
broad, gently sloping sides, circular base
layers of basaltic lava
steep sides, generally small
basaltic and/or andesitic
greater than shield volcanoes
Izalco volcano in El Salvador
much larger than cinder-cone volcanoes
violently explosive, greatest danger to humans
Mount St. Helens, WA
C. Volcanoes at the beginning of Earth's history
The Earth formed from a nebular cloud about 4.6 billion years ago.
About 4 billion years ago, Earth began to cool and the first rocks formed on the surface.