| A | B |
|---|
| magma | liquid rock produced under Earth's surface |
| volcanism | any activity that includes the movement of magma toward or onto Earth's surface |
| lava | magma that flows onto Earth's surface; the rock that forms when lava cools and solidifies |
| volcano | a vent or fissure in Earth's surface through which magma and gases are expelled |
| subduction zone | where one tectonic plate moves under another |
| trench | forms on ocean floor alon the edge of the continent where the plate is subducted |
| island arcs | a string of of volcanic islands that form along colliding plates where subduction occurs |
| pillow lava | volcanic rock that forms underwater at a mid-ocean ridge. Caused by water rapidly cooling its outer surface |
| fissures | cracks through which lava flows to Earth's surface |
| hot spot | a volcanically active area of Earth's surface, commonly far from a tectonic plate boundary |
| mantle plumes | columns of solid, hot material from the deep mantle rise and reach the lithosphere. |
| mafic | describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color |
| felsic | describes magma or igneous rock that is rich in feldspar and silica and that is generally light in color |
| pyroclastic material | fragments of rock that form during a volcanic eruption |
| ash | pyroclastic particles less than 2mm in diameter |
| lapilli | Latin for "little Stones", less than 64mm in diameter |
| volcanic bombs | pyroclastic material that are known as volcanic blocks, can be the size of a house |
| volcanic dust | less than .25mm in diameter |
| crater | funnel-shaped pit at the top of a volcanic vent |
| caldera | a large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink |
| shield volcano | Volcanic cones that are broad at the base and have gently sloping sides. |
| cinder cones | A type of volcano that has very steep slopes. Explosive eruptions and are made of pyroclastic material |
| Composite Volcanoes | Made up of alternating layers of hardened lava flows and pyroclastic material. Also known as stratovolcanoes |
