 | Term | Definition |
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Why does magma rise? |
Magma rises because it is less dense than the surrounding crust. I rises until it reaches the surface or becomes trapped under a rock layer. |
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What happens as magma rises? |
The gases in the magma decrease in pressure. The gases separate and form bubbles. |
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When does a volcano erupt? |
When the gases in magma rush out of a weak spot in the crust. |
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Characteristics of a volcano |
See page 185 - Crater, pipe, side vent, vent, magma chamber. |
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Crater |
The bowl-shaped area that forms around the volcano's vent. Lava collects in the crater. |
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Pipe |
A narrow, almost vertical crack in the crust through which magma rises to the surface. |
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Side Vent |
Sometimes magma forces its way out of a volcano through this. |
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Vent |
Teh point on the surface where magma leaves the volcano's pipe. |
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Magma Chamber |
A large underground pocket that forms as magma rises toward the surface. |
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What are the 4 factors that affect the force of a volcanic eruption? |
Gas content, temperature, thickness, silica content. |
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What is viscosity? |
A fluid's ability to flow. Viscosity is affected by gas content, temperature, thickness, silica content. Examples: water has a low viscosity, maple syrup a higher one. |
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When do quiet eruptions occur? |
When the viscosity of lava is low. |
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What is a Pahoehoe? |
Fast moving, ropey lava with a low viscosity. |
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What is a Aa? |
Lava with a low viscosity that is cooler and moves slowly. |
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When do explosive eruptions occur? |
When lava is thick and has a high viscosity. This lava does not rush out of the volcano. It builds up in the pipe and explodes when maximum pressure is reached. The explosion breaks lava into fragments of varying sizes. |
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Ash |
Fine grained lava. |
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Cinders |
Pebble-sized lava. |
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Bombs |
Lava the size of a baseball or a car. |
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Pyroclastic flow |
Produced by ash, cinders and bombs when an explosion occurs. |
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What are the 3 states of a volcano? |
Dormant, active, extinct. |
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Active volcano |
One that is erupting or shows signs that it may erupt in the near future. |
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Dormant volcano |
One that scientists expect will awake in the future. |
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Extinct volcano |
One that is unlikely to erupt ever again. |
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Hot springs |
Volcanic activity that occurs when groundwater becomes heated due to a nearby body of magma. |
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Geyser |
Groundwater that becomes heated, trapped below the surface and suddenly explodes. |
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Geothermal energy |
Type of energy derived from naturally occuring volcanic areas like hot springs and geysers. Hot water can be transferred to homes to keep them warm. Steam that is trapped underground can be used to spin turbines which generate electricity. |
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Is a volcanic eruption or an earthquake more predictable? |
Volcanic eruption. |
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What are indicators of volcanic activity? |
Tiltmeters, laser-ranging devices, water temperature changes, earthquakes, any movement in magma. |
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Why do people live near volcanoes? |
Because the soil on a volcanic mountain is rich and fertile. |
