Volcano

A volcano is an opening in the ground. Hot liquid rock called lava comes out from deep below. Ash and gases also escape from volcanoes. This happens because there is very hot melted rock stored underneath the Earth.

Most volcanoes on Earth are found underwater in the oceans. They form where the Earth's hard outer shell is breaking apart or pushing together. When the shell breaks apart, volcanoes usually erupt gently. When pieces of the shell push together, volcanoes explode very violently. Some volcanoes form in other special places where the Earth's crust is stretching and getting thinner.

Deep inside the Earth, very hot rock can rise up from far below, almost 2,000 miles down. This hot rock can create volcanoes in the middle of the ocean or in the middle of land. As the ground moves over time, this creates chains of volcanic islands, like the Hawaiian Islands.

Volcanoes are sorted into three types based on how often they erupt. Active volcanoes have erupted before and will probably erupt again. Dormant volcanoes have not erupted for a very long time, but they might erupt someday. Extinct volcanoes will never erupt again because they have no hot rock left inside them. When big volcanoes erupt, ash fills the sky and blocks the sun. This makes the Earth cooler for a while, which can hurt crops and people.

Other planets and moons have volcanoes too. Venus has many volcanoes. Mars has big volcanoes as well. Some moons even have cold volcanoes that spray ice instead of hot rock.