Volcanoes are mountains that form when magma reaches the surface of Earth. Under certain conditions, small amounts of mantle rock can melt, forming liquid magma. The magma rises upwards through the crust, erupting at the surface as a volcano. A volcano is composed of a magma chamber, pipes, vents, a crater, and a caldera. The magma chamber is the pocket where magma collects. Pipes are narrow, vertical channels where magma rises to the surface. Vents are openings in the Earth's surface where magma escapes through the Earth. A crater is a bowl-shaped pit at the top of the volcano. A caldera is a collapsed magma chamber and vent. There are two types of volcanoes, shield volcanoes, and composite volcanoes. A shield volcano is a wide, flat volcano which erupts low-viscosity lava. A composite volcano forms from explosive eruptions that produce a combination of lava and ash.
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