| A | B |
|---|
| volcano | a weak spot in the crust where magma has come to the surface. |
| magma | the molten rock from the mantle which has not reached the surface |
| lava | liquid magma that reaches the surface. |
| 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 found in magma that is formed from the elements oxygen and silicon |
| 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| extinct | describes a volcano that is no longer active and is unlikely to erupt again |
| geyser | a fountain of water and steam that builds up pressure underground and erupts at regular intervals |
| shield volcano | a wide, gently sloping mountain made of layers of lava and formed by quiet eruptions |
| cinder cone | a steep, cone-shaped hill of 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 | the large hole at the top of a volcano vormed 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 (a magma intrusion!) |
| sill | a slab of volcanic rock formed when magma squeezes between LAYERS of rock |
| intrusion | an igneous rock layer formed when magma hardens Earth's surface |
| batholith | a mass of rock formed when a large body of magma cools inside the crust |
| basin | a broad, bowl-shaped valley formed where the crust is bent downward |
| Central Valley | the large basin in California between the Coast Ranges and the Sierra Nevada |
