| A | B |
|---|
| 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 part of 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 move 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; silica 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 expolsive 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 |
| extinct | said of a volcano that is unlikely to erupt again |
| hot spring | a pool fromed 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 eruptions |
| 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 |
