What is a volcano?
A volcano is an opening in Earth's crust where molten rock, called magma, along with gases and ash, escapes to the surface. Over time, eruptions can build mountains.
Deep below the surface, heat melts rock into magma. Because magma is lighter than the surrounding rock, it rises and collects in chambers. When pressure builds up, it can push through cracks and erupt. Once magma reaches the surface, it is called lava. Eruptions can be gentle lava flows or violent explosions of ash and rock.
There are several types of volcanoes. Shield volcanoes, like Mauna Loa in Hawaii, have gentle slopes built by runny lava. Stratovolcanoes, like Mount Fuji, are steep and built from layers of lava and ash, often with explosive eruptions. Cinder cones are smaller and built from loose fragments.
Active volcanoes
There are about 1,350 potentially active volcanoes on land, plus many more under the oceans. Most are found along tectonic plate boundaries, especially the Ring of Fire around the Pacific Ocean. Scientists monitor volcanoes for earthquakes, gas changes and ground swelling to warn of eruptions.
Did You Know?
Olympus Mons on Mars is the largest known volcano in the solar system, about 22 kilometers high and roughly the size of Arizona.