| Term | Definition |
|---|
| volcano | a weak spot in the crust where molten material, or magma, comes to the surface |
| magma | a molten mixture of rock-forming substances, gases, and water from the mantle |
| lava | the result of when magma reaches the surface |
| Ring of Fire | a major volcanic belt surrounding the rim of the Pacific Ocean |
| island arc | when the crust moving over a hotspot forms a ring of islands |
| hot spot | an area where material from deep within the mantle rises and then melts, forming magma |
| viscosity | the resistance of a liquid to flowing |
| silica | a compound that is made up of particles of the elements oxygen and silicon |
| pahoehoe | fast-moving, hot lava that has low viscosity |
| aa | cooler, slower moving lava with high viscosity |
| magma chamber | the pocket beneath a volcano where magma collects |
| pipe | a long tube that connects the magma chamber to Earth's surface |
| vent | the opening through which molten rock and gas leave the volcano |
| lava flow | the area covvered by lava as it pours out of a vent |
| crater | a bowl-shaped area that may form at the top of a volcano around the central vent |
| pyroclastic flow | when an explosive eruption hurls out a mixture of hot gases, ash cinders, and bombs |
| crater | the depression in the Earth where a volcano's top was bloen off as a result of an explosive eruption |
| dormant | a volcano that is expected to awaken in the future and become active |
| extinct | a volcano that is unlikely to erupt again |
| shield volcano | the type of volcano formed from when lava flows gradually to build a wide, gently sloping mountain |
| cinder cone | the type of volcano formed from when asch, cinders, and bombs build up around the vent in a steep, cone-shaped hill or small mountain |
| composite volcano | the type of volcano formed from when layers of lava alternate with layers of ash to form tall, cone-shaped mountains |
| caldera | the huge hole left by the collapse of a volcanic mountain |
| geothermal activity | when magma a few kilometers beneath Earth's surface |
| geyser | a fountain of water and steam that erupts from the ground |
| country rock | the rock surrounding and penetrated by mineral veins or igneous intrusions |
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