Volcanoes 1 Flashcards
What is the distribution of volcanoes similar to?
very similar to earthquakes but not exactly the same
Magma
high temperature, molten or(mostly molten) rock material with a wide range of compositions(silica almost always present)
Where does melting actually occur?
-in the overriding plate
Classifications of Magma
Lowest silica content- basaltic magma at 50%
Intermediate silica content- andesitic magma at 60%
Highest silica content- rhyolitic magma at 70%
Melting Temperatures
Low silica around 1200
High Silica 700-900
Dissolved volatiles such as gas and fluids determine what?
eruptive behavior
Flood or Plateau Basalt
very liquid lava; flows very widespread; emitted from fractures
ex: columbia river plateau
Shield Volcano
- liquid lava
- emitted from a central vent
- large
- sometimes has a caldera collapse
ex. Hawaiian Volcanoes
Cinder Cone
- explosive liquid lava
- small
- emitted from a central vent
- if long enough may build up a shield volcano
ex. Crater of the moon
composite or stratovolcano
- more viscous lavas
- explosive debris
- large
- emitted from a central vent
ex. Mount Rainer, Mount St, Helens
volcanic dome
- very viscous lava
- relatively small
- can be explosive
- commonly occur adjacent to crater of composite volcanoes
ex. Mount St. Helens Lava Dome
Caldera
very large composite volcano collapsed after an explosive period
-frequently associated with plug domes
Lava
is magma that has been extruded from a volcano
Elemental Composition of Magma
- O
- Si
- Fe
- Al
- Mg
- Ca
- Na
- K