| A | B |
|---|
| Volcano | A weak spot in the crust where magma has come to the surface. |
| Hot spot | An area where magma from deep within the mantle melts through the crust above it. |
| Ring of Fire | A major belt of volcanoes that rims the Pacific Ocean. |
| Magma | The motlen mixture of rock-forming substances, gases, and water that makes up part of the Earth's mantle. |
| Lava | Magma that reaches the surface; also the rock formed when liquid lava hardens. |
| 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 thtat is unlikely to erupt again. |
| aa | A slow-moving type of lava that hardens to form rough chunks. |
| caldera | The large hole at the top of a volcano formed when the roof of a volcano's magma chamber collapses |
| cinder cone | A steep, cone-shaped hill or mountain made of volcanic ash, cinders, and bombs pilded 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. |
| crater | A bowl-shaped area that forms around a volcano's central opening. |
| island arc | A string of islands formed by the volcanoes along a deep ocean trench. |
| magma chamber | The pocket beneath a volcano where magma collects. |
| pahoehoe | A hot, fast-moving type of lava that hardens to form smooth, ropelike coils. |
| pipe | A long tube through which magma moves from the magma chamber to Earth's surface. |
| pyroclastic flow | The expulsion of ash, cinders, bombs, and gases during an explosive volcanic eruption. |
| sheild volcano | A wide, gently sloping mountain made of layers is lava and formed by quiet eruptions. |
| vent | The opening through which molten rock and gas leave a volcano. |
