The Earth's crust, on which we live and depend, is in large part the product of millions of once-active volcanoes and tremendous volumes of magma, some of which did not make it to the Earth's surface. Volcanic ash increases soil fertility for forests and agriculture by adding nutrients and acting as mulch. Groundwater heated by hot magma can be tapped for geothermal energy. This hot groundwater has also concentrated valuable minerals, including copper, tin, gold and silver, which are mined throughout the world.

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