If so, an eruption begins.Įast Summit is on the left skyline, and North Summit, to its right, is topped by an ice-filled crater from which a blocky dacite lava flow extends 1 km toward the camera. It is driven towards Earth's surface by buoyancy, it is lighter than the surrounding rock, and by pressure from gas within it. Magma forces its way upward and may ultimately break though weak areas in the Earth's crust. Originating many tens of miles beneath the ground, magma is lighter than surrounding solid rock. After cooling, liquid magma may form crystals of various minerals until it becomes completely solid and forms an igneous or magmatic rock. The molten rock is made of the chemicals oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium, titanium, and manganese. Molten rock below the surface of the Earth that rises in volcanic vents is known as magma, but after it erupts from a volcano it is called lava. Magma is made of molten rock, crystals, and dissolved gas-imagine an unopened bottle of soda with grains of sand inside. Illustration of the basic process of magma formation, movement to the surface, and eruption through a volcanic vent.
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