The Earth consists of three layers. The outer layer of Earth we live on is called the crust, it’s about 18 miles thick. Below the crust lies a 1,800 mile thick layer called the mantle. A combination of molten rock and gases called magma lies between the Earth’s crust and the mantle.
A volcano is a mountain that extends down to a pool of magma between the crust and mantle. It’s basically a hole in the Earth from which magma can erupt through the surface.
If a volcano erupts suddenly in a heavily populated area, the result can be a devastating amount of deaths and the destruction of towns, industries, and vegetation.
But volcanoes bring benefits as well. They provide fertile soils and natural energy from there heat. Lava flows can also build new land, as they have in Hawaii.