Volcanic Geomorphology

Volcanic Geomorphology - Volcanic 1 Volcanic Geomorphology...

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Volcanic: 1 Volcanic Geomorphology Below the Surface At the Surface Other Related Phenomena When we discussed rocks, we went over igneous rocks and how they form. They originate as molten rock material that cools and solidifies. If it solidifies beneath the surface, it is an intrusive igneous rock and if it cools at the surface it is extrusive. Now we are turning our attention to the landforms created by these processes. Below the Surface (Plutonic Features) Below the earth's surface the asthenosphere is partially molten. Along weak spots in the crust, magma (molten rock material) rises toward the surface. Sometimes it reaches the surface and erupts as lava before it cools and solidifies. Most, but not all, volcanoes are found along plate boundaries. Hawaii is a good example of an exception- the islands are found over a hot spot in the crust. Most magma cools and solidifies before it gets to the surface. If magma cools as a large mass beneath the surface, it is called a batholith . The Sierra Nevada in California are made up mostly of a batholith which is now at the surface after all of the material overlying it has been eroded away. Sometimes magma cools as it is moving toward the surface in cracks in the crustal rock. If the crack was vertical, we call the resulting rock a dike and if it was moving horizontally when it hardened, it is called a sill . Dikes and sills can also be exposed at the surface if the overlying material is eroded away. These things that form below the surface are called plutonic features batholith- large mass dike- vertical sill- horizontal
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Volcanic: 2 At the Surface If magma gets to surface before it solidifies, then it becomes a volcanic eruption. There are two basic types of material involved: lava and pyroclastic material. Combinations of the two are common. Lava is molten rock at the surface. When it gets to the surface it flows out and cools relatively quickly because it is exposed to the air, which is much cooler than where the magma came from. There are two
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Volcanic Geomorphology - Volcanic 1 Volcanic Geomorphology...

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