| A | B |
|---|
| volcano | a mountain that forms in Earth’s crust when molten material, or magma, reaches the surface |
| magma | a molten mixture of rock-forming substances, gases, and water from the mantle |
| lava | the name for magma when it reaches the surface |
| Ring of Fire | one major belt of volcanoes long the coasts of the Americas, Japan, and Philippines |
| island arc | the string of islands resulting from magma that breaks through the ocean floor |
| hot spot | an area where material deep within Earth’s mantle rises through the crust and melts to form magma |
| magma chamber | a pocket of magma beneath the surface |
| pipe | a long tube that extends from Earth’s crust up through the top of a volcano |
| vent | an opening where molten rock and gas leave a volcano |
| lava flow | the spread of lava as it pours out of a vent |
| crater | a bowl-shaped area that may form at the top of a volcano around a vent |
| silica | a material found in magma that forms from the elements oxygen and silicon |
| pyroclastic flow | the mixture of hot gases, ash, cinders, and bombs that flow from a volcanic eruption |
| dormant | a volcano that scientists expect to awaken in the future |
| extinct | a volcano that is unlikely to ever erupt again |
| caldera | the hole left when a volcano collapses |
| dike | magma that forces itself across rock layers and hardens |
| sill | magma that squeezes between horizontal rock layers and hardens |
| volcanic neck | forms when magma hardens in a volcano’s pipe and the surrounding rock layer wears away |
| batholith | a mass of rock formed when a large body of magma cools inside the crust |
