Terminology:
Magma
– Molten rock on the ground (from the mantle).
Lava
– Magma when it reaches the surface and is exposed to air
Magnitude
– How big it is e.g size of volcanic eruptions
Types
Of Volcanic Eruptions:
- Rock types are the main factor determining volcanic properties
- Basalt comes from constructive boundaries
- Rhyolite near destructive boundaries
- More silica = more stick the tick and lower temperature. The gas becomes trapped = more explosive volcano.
- Low silica = hot, runny lava. Less gas = less explosive volcano
- Basalt is 48-52%, Rhyolite is 68-77%
- Basalt is 1160, Rhyolite is 900 (degrees)
- Destructive margins have cooler, sticky (high silica) lava which is explosive as the gas is under pressure. Creates steep-sided stratovolcano e.g Mt St Helens.
- Constructive margins and hotspots have runny (low silica) lava that isn’t explosive which create shield volcanoes like the Hawaiian Islands.