Chapter 18: Volcanic Activity Flashcards
explain how magma forms. 3 factors
- temperature hot enough to melt the rocks (800 to 1200)
- pressure (temperature needed to melt increases with pressure)
- water (rocks with water will melt at higher temperatures)
Basaltic Magma
when rocks in the mantle melt
Andestic Magma
continental margins where oceanic crust is subducted into the Earth’s mantle
Rhyolitic Magma
molten material that rises and mixes with overlying silica and water rich continental crust
pluton
intrusive igneous rock bodies made from minerals mixing
baolith
the largest plutons
laccolith
mushroom shaped pluton with round top and a flat bottom
sill
pluton that forms when magma intrudes paralell layers of rock
Dike
pluton that cuts across preexisting rocks
stocks
small-irregular shaped plutons
calderas
large volcanic depressions
shield volcano
mountain with broad, gently sloping sides and a nearly circular base.
ex. Hawaii Mauna Loa
Cinder Cone Volcanoes
small with steep sides. (no more than 500m)
ex. Izalco in El Salvador
Composite volcanoes
very large, lots of explosions, dangerous
ex. Mt St Helens
tephra
rock fragments thrown into the air during a volcanic eruption
pyroclastic flow
gas, ash, and other tephra flowing down a slope at incredibly high speeds. May contain hot, poisonous gasses.
where do volcanoes form
plate boundaries (80 percent at convergent boundaries)
convergent volcanism
convergence of oceanic plate creates seduction zones, places where slabs of oceanic crust descend into the mantle and eventually melt. The magma generated is forced upward through the overlying plate and forms volcanoes when it reaches the surface
divergent volcanism
two plates move apart, magma is forced up through the fractures and faults that form as the plates separate
hot spots
unusally hot regions of Earth’s mantle where high-temperature plumes of mantle material rise to the surface