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Volcanic Hazards Lesson

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What Creates a Volcano?

Volcanoes are created by layers of lava, pyroclastic material, ash or a combination of all build up around a central vent. Molten rock from the Earth’s interior is ejected via the central vent or, in some cases, on the flank, of the volcano.

Location, location, location

Recall that volcanoes either form at divergent plate boundaries, subduction zones or above hot spots.

Subduction zones (10%)

Stratovolcanoes are the most common volcano that forms via subduction zones. The form due to volatiles from the subducting plate initiate melting, which rises to the surface to form arc volcanoes on overriding plate.

Spreading centers (80%)

Most of the lava on Earth erupts along mid-ocean ridges. This makes sense when you realize that the mid-ocean ridges snake about the surface of our planet for roughly 80,000 km (49,700 mi)!

Hot spots (10%)

Oceanic hot spots - Basaltic magma erupts at the seafloor, forms a growing mound. This volcano will continue to grow. If it rises above sea level it will become an island.

Continental hot spots - These volcanoes often erupts both basaltic and rhyolitic material.

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