| Term | Definition |
|---|
| Volcano | A weak spot in the crust where magma has come to the surface |
| Magma | The molten mixture of rock- forming substances, gases, and water that makes up a part of the earth's mantle |
| Lava | Magma that reaches the surface; also the rock formed when liquid lava hardens |
| Ring of Fire | A major belt of volcanoes that rims the Pacific Ocean |
| Island Arc | A string of islands formed by the volcanoes along a deep ocean trench |
| Hot Spot | An area where magma from deep within the mantle melts through the crust above it |
| Magma Chamber | The pocket beneath a volcano where magma collects |
| Pipe | A long tube through which magma moves from the magma chamber to Earth's surface |
| Vent | The opening through which molten rock and gas leave a volcano |
| Lava Flow | The area covered by lava as it pours out of a volcano's vent |
| Crater | A bowl- shaped area that forms around a volcano's central opening |
| Silica | A material that is formed from the elements oxygen and silicon; it is found in magma |
| Pahoehoe | A hot, fast moving type of lava that hardens to form smooth, ropelike coils |
| Aa | A slow-moving type of lava that hardens to form rough chunks; cooler than pahoehoe |
| Pyroclastic Flow | The expulsion of ash, cinders, bombs, and gases during an explosive volcanic eruption |
| Active | Said of a volcano that is erupting or has shown signs of erupting in the near future |
| Dormant | Said of a volcano that does not show signs of erupting in the near future (sleeping) |
| Extinct | Said of a volcano that is unlikely to erupt again |
| Hot Spring | A pool formed by groundwater that has risen to the surface after being heated by a nearby body of magma |
| Geyser | A type of hot spring that builds up pressure underground and erupts at regular intervals as a fountain of water and steam |
| Geothermal Energy | Heat energy in Earth's interior from water or steam that has been heated by magma |
| Shield Volcano | A wide, gently sloping mountain made of layers of lava and formed by quiet eruption |
| Cinder Cone | A steep, cone- shaped hill or mountain made of volcanic ash, cinders, and bombs piled up around a volcano's opening |
| Composite Volcano | A tall, cone- shaped mountain in which layers of lava alternate with layers of ash and other volcanic materials |
| Caldera | The large hole at the top of a volcano formed when the roof of a volcano's magma chamber collapses |
| Volcanic Neck | A deposit of hardened magma in a volcano's pipe |
| Dike | A slab of volcanic rock formed when magma forces itself across rock layers |
| Sill | A slab of volcanic rock formed when magma squeezes between layers of rock |
| Batholith | A mass of rock formed when a large body of magma cooled inside the crust |
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