Volcano
Volcano is a mountain that forms when magma reaches the surface. Under certain conditions, small amount of mantle rock can melt, forming liquid magma. The magma rises upward through the crust, erupting at the surface as a volcano.
Magma Chamber• A pocket where magma is collected
Caldera• A huge depression created by the empty chamber (hollow shell) collapsing inward
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Pipe• Narrow, vertical channel where magma rises
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Vent• An opening in the ground where escapes to the surface
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Crater• Bow-shaped pit at the top of the central vent in most volcanoes
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Volcanoes erupt explosively or quietly, depending on the characteristics of the magma.
Viscosity• The resistance to flow
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High Viscosity• Thick and resists easily
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Low Viscosity• Thin and flows easily
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Temperatures, water content, silica content=determine the viscosity of magma
Higher temperature=lower viscosity
Water=flow more easily
High in silica=high viscosity
Higher temperature=lower viscosity
Water=flow more easily
High in silica=high viscosity
Quiet Eruptions• Very hot, low-silica magma
• Travel for great distance • Two lavas=pahoehoe, aa • Pahoehoe=hot, fast-moving lava with a replica surface • Aa=cooler, slow-moving lava with a chunky, crumbly appearance |
Explosive Eruptions• High-silica magma
• Clog the pipe=increase in pressure • Solidifies very quickly and shatters into pieces of different sizes |
Most volcanoes occur along plate boundaries or at hot spots in the crust
Ring of Fire• The trenches at the rim of Pacific ocean
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Hot Spot• A region where hot rock extends from deep within the mantle to the surface
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The three major types of volcano are Shield volcanoes, Cinder cones, Composite volcanoes
Shield Volcanoes• Wide, flat volcano produced by a quiet eruption
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Cinder Cones• Small, steep-sided volcano produced by an eruption of ash and cinders
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Composite Volcanoes• Formed from explosive eruptions that produce a combination of lava and ash
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Igneous features formed by magma include Batholiths, Sills, Dikes, and Volcanic necks
Batholiths• The largest type of intrusive igneous rock mass
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Sills• Magma squeezes into a crack between layers if rock and then hardens. If the crack is parallel to existing rock layers, the magma hardens into a structure
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Dikes• If the crack cuts across rock layers, the hardened magma forms dike
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Volcanic Necks• The magma hardened in a volcanic pipe
• Lava plateau=layers of hardened lava may form a high, level area |