Definition: an opening in a planet's surface of crust which allows hot, molten rock, ash and gases to escape from below the surface.
Causes: (You don't have to remember all the details, just need to remember the underlined parts. I just put the details in here so it can make more sense.)
1. When two plates are coming apart (diverging). This usually happens in the ocean. Two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock. Because the new crust is very thin, magma is able to come out.
2. When two plates are coming together (converging). This usually happens where the ocean and the continent meet. When a oceanic plate and a continental plate collide, the oceanic plate goes under the continental plate, forming a trench. Water thus released lowers the melting temperature of the overlying mantle wedge, creating magma.
3. Hotspots. Certain volcanic areas where columns of hot materials rising from the core-mantle boundaries.
Land forms created by Volcanoes:
1. Mountains - 3 types: cinder cone, shield volcano, and composite volcano.
* Cinder Cone: small, cone-shaped volcano with steep sides. Short and explosive eruptions. Usually erupt only once. Example: Diamond Cinder Cone in St. George.
*Shield Volcano: a large volcano shaped like a flattened dome. Quiet, non-explosive eruptions with slow-flowing lava. Examples: Cedar Hill in Utah; Hawaiian Shield Volcanoes.
*Composite Volcano: tall and large volcano with steep sides. Large explosive eruptions. Most threatening. Examples: Mount Hood in Oregon.
3. Islands, like Hawaii.
How to predict: tiltmeter