Lava is the molten or melted rock that is forced from volcanoes and cracks within the Earth's surface, as well as what is left behind once it cools and hardens. Cooled lava has formed many mountains and island chains, and much of it eventually becomes lush and productive soil. Lava is made up of mostly silicon dioxide, and geologists believe magma (the term used to describe the molten rock deep with the Earth) is created under extreme pressure and temperatures at great depths below the Earth's crust. When a volcano erupts, molten rock is forced up through the Earth's crust and expelled out as lava, which can reach temperatures as high as 2,000 degrees Fahrenheit (1,200 degrees Celsius).
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