| A | B |
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| Volcano | A vent in the Earth's crust through which lava, steam, ashes are expelled, either continuously or at irregular intervals |
| Subduction Zone | Occurs when two tectonic plates move towards one another and one plate slides underneath the other, moving down into the mantle |
| Mount St. Helens | A visible volcano found in the USA |
| Hotspot | Region of the Earth's upper mantle that up wells to melt through the crust to form a volcanic feature |
| Hawaii | An example of a hotspot volcano |
| Molten Rock | A liquid that lies beneath the Earth’s surface and is made up of minerals and gasses |
| Lava | Is what magma is called when it reaches the surface |
| Magma | Molten rock in the earth's crust |
| Guyots | Formed when some islands are eroded by waves and form flat- topped sea mounts |
| Extrusive rock | Igneous rock formed by the crystallisation of magma above the surface of the Earth |
| Intrusive rock | Igneous rock formed by the crystallisation of magma below the surface of the Earth |
| Basaltic (basic) lavas | Originate largely from the upward movement of mantle material. They are most common along spreading ridges but are also found at hotspots within more developed rift systems |
| Andesitic (intermediate) lavas | Are typical of destructive plate margins where crust is being destroyed |
| Rhyolitic (acid) lavas | Are most often found at destructive and collision margins |
| Fissure Eruptions | Occur where an elongated crack in the crust allow lava to spill out over a large area |
| Shield volcanoes | Are made of basaltic rock and form gently sloping cones from layers of less viscous lava |
| Composite volcanoes | The most common type found on land. They are created by layers of ash from initial explosive phases of eruptions and layers of lava from the main eruption phases |
| Acid or dome volcanoes | These are steep- sided volcanoes formed from very viscous lava |
| Calderas | Form when gases that have built up beneath a blocked volcanic vent result in a catastrophic eruption that destroys the volcano summit. Leaves an enormous crater where later eruptions may form smaller cones |
| Volcanic Explosivity Index | Relative measure of the explosiveness of volcanic eruptions |
