| A | B |
|---|
| volcano | a weak spot in the crust where magma has come to the surface |
| magma | the molten mixtureof rock-forming substances, gases, and water from the mantle |
| lava | liquid magma that reaches the surface: alsothe 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 volcanos aling a deep-ocean trench |
| hot spot | an area where magma from deep within the mantle melts through the crust above it |
| element | a substance that cannot be broken down into other substances |
| compound | a substance in which two or more elements are chemically joined |
| physical property | any characteristic of a substance that can be observed or measured without changing the composition of the substance |
| chemical property | any property of a substance that produces a change in the composition of matter |
| viscosity | the resistance of a liquid to flowing |
| silica | a material found in magma that is formed from the elements oxygen and silicon |
| 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 |
| magma chamber | thepocket 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 purs out of a volcano's vent |
| crater | a bowl shaped area that forms around a volcano's central opening |
| pyroclastic flow | the expulsion of ash,cinders,bombs and gases during an explosive volcanic eruption |
| dormant | describes a volcano that is not currently active, but that may become active in the future |
| extinct | describes a volcano that is no longer active and is unlikely to erupt again |
| 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 small 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 | a large hole at the top of a volcano formedwhen 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 cools inside the crust |
| geothermal activity | the heating of underground waterby magma |
| geyser | a fountain of water and steam that builds up pressureunderground and erupts at regular intervals |
