Many of the world’s mountains are volcanoes. When Earth’s tectonic plates bump into each other, pull apart, or slide under one another, magma sometimes pours out through cracks in the crust, in the form of lava.
Most of the time, this occurs along the edges of tectonic plates. Some volcanoes form in the middle of plates as they move across areas in the mantle that are so hot, magma erupts right through the crust. This is called a hot spot. The Hawaiian Islands sit on top of a hot spot.
A volcanic eruption is a violent event. Earthquakes may occur before the eruption even begins. Clumps of lava and volcanic rock may explode high into the air, accompanied by thick, suffocating clouds of gas and ash. Rivers of fiery lava may travel for miles. A single volcano can cause enormous damage. But soon, the boiling-hot lava and the ash harden back into rock, causing a new mountain to become higher or an old one to change shape.
