What causes a volcano to form?


A volcano forms when rock from the Earth's mantle melts, moves to the surface and releases lava. Lava is liquid rock (magma) that has reached the Earth's surface.

The mantle is a solid body of rock between the Earth's thin surface crust and its molten iron core. High temperature and pressure causes the mantle to melt and become liquid rock, known as magma.

When a large amount of magma forms, it rises through the layers of rock toward the surface of the Earth. As it moves upward, the overlying rock pressure decreases. This allows carbon dioxide, sulfur dioxide and water vapor to emerge, which pressurizes the magma further.

The magma is now called lava as it erupts through the opening. When lava, gas and ash reach the surface, a volcano is erupting.

Volcanoes can also form when tectonic plates collide and lava and gases build up around the opening in the surface, resulting in cone-shaped, steep volcanoes. Mount Rainier is an example of this type of volcano, called a stratovolcano.

Some eruptions are so violent that the volcano top collapses, which creates a pit called a caldera. There are calderas at Crater Lake and Yellowstone National Park.

Volcanoes are considered active if they have erupted sometime during the past 10,000 years.

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Ask.com Answer for: what causes a volcano to form
Volcanoes are created from a opening in the Earth's crust, which allows hot magma, ash and gases to escape. They form in the shape of cones, domes or simple fissures.
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