| 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 from the mantle. |
| lava | liquid magma that reaches the surface; also, the rock formed when liquid lava hardens. |
| Ring of Fire | volcano belt 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. |
| pyroclastic flow | an explosive volcanic eruption of ash, sinders, bombs, and gases. |
| extinct | a volcano that is no longer active and is unlikely to erupt again. |
| fissures | large cracks in the Earth's crust. |
| basin | a broad, bowl-shaped valley formed where the crust is bent downward. |
| dormant | a volcano that is not currently active, but that may become active in the future. |
| intrusion | an igneous rock layer formed when magma hardens beneath Earth's surface. |
| batholith | a mass of rock formed when a large body of magma cools inside the crust. |
| vent | opening through which magma leaves a volcano. |
| silica | a material found in magma that is formed from the elements oxygen and silicon. |
| crater | a bowl-shaped area that forms around a volcano's opening. |
| shield volcano | a wide, gently sloping mountain made of layers of lava; formed by quiet eruptions. |
| cinder cone | a steep, cone-shaped hill or small mountain made of volcanic ash, cinders, and bombs. |
| composite volcano | a tall, cone-shaped mountain in which layers of lava and ash alternate.(take turns.) |
| 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. |
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