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Volcanism 13-1
Volcanoes and Plate Tectonics
| Question | Answer |
|---|---|
| Magma | Liquid rock produced under Earth's surface |
| Volcanism | Any activity that includes the movement of magma toward or onto Earth's surface |
| Lava | Magma that flows onto Earth's surface; the rock that forms when lava cools and solidifies |
| Hot spot | A volcanicallyactive area of Earth's surface, commonly far from a tectonic plate boundary |
| Ring of Fire | One of Earth's major eathquake and volcano zones, formed by the subduction of plates along the Pacific coasts of N. America, S. America, Asia, and the islands of the western Pacific Ocean. |
| Subduction zone | Where one tectonic plate moves under another |
| Island arc | A string of volcanic islands |
| Fissure | Cracks through which lava flows to Earth's surface |
| Mantle plume | Where columns of solid, hot material from the deep mantle rise and reach the lithosphere. |
| Pluton | Large formations of igneous rock formed by magma that cooled and solidified inside the crust |
| Batholith | Large plutons that cover an area of at least 100 kilometers squared when they are exposed on Earth's surface. |
| Dike | Small plutons that are tabular in shape. Some may be only a few centimeters wide. |
| Mafic | Describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color |
| Felsic | Describes magma or igneous rock that is rich in feldspars and silica anad that is generally light in color |
| Viscosity | Resistance to flow |
| Quiet Eruption | Oceanic volcanoes that, because of mafic magma's low viscosity, gases escape from easily. Called so because they are usually quiet. |
| Pahoehoe lava | Forms pahoehoe rock when cooled. Wrinkly rocks when cooled. Means "ropy" in Hawaiian. |
| Aa lava | Forms Aa rock which looks like jagged rocks. Same composition as Pahoehoe lava, but different gas content and rate and slope of the lava flow. |
| Blocky lava | Higher silica content then Aa lava. Higher viscosity. Forms "blocky" rock. |
| Explosive eruption | When felsic lavas erupt from continental volcanoes, the lava is cooler and stickier. They also contain trapped gases, so when a volcano erupts, they escape. Also tend to spray pyroclatic material. |
| Pyroclastic material | Fragments of rock that form during a volcanic eruption |
| Volcanic ash | Pyroclastic particles that are less than 2 millimeters in diameter |
| Volcanic dust | Volcanic ash that is less than 0.25 millimeters in diameter. |
| Lapilli | Large pyroclastic particles that are less than 64 millimeters in diameter. Means "little stones" in Latin |
| Volcanic bomb | Large clots of lava that are thrown out of an erupting volcano. Develop a round or spindle shape. |
| Volcanic block | Largest pyroclastic materials formed from solid rock that is blasted from the vent. Some are the size of a small house. |
| Shield volcano | Volcanic cones that are broad at the base and have gently sloping sides. Covers a wide area and is formed from quiet eruptions. |
| Cinder cone | A volcano that has very steep slopes. Form from small explosive eruptions, made of pyroclastic material. Smaller than shield or composite volcanoes. |
| Composite volcano | A volcano that is made of alternating layers of hardened lava flows and pyroclastic material. Quiet to explosive, then back again. |
| Caldera | A large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink. |
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