The earth has an outer shell called crust. There are cracks in the crust and that's called a volcano. The reason that volcanoes erupt is that the magma that is underground gets so hot that it goes up and ERUPTS and then the lava goes everywhere. Craters are the opening of a volcano that can be many miles wide. A vent is in a crater. Ash, dust, and lava come out of vents and craters. A magma chamber is an underground area with thick molten rock in it.
Most volcanoes are dormant. Sometimes volcanoes are so dormant they have not even erupted for a long time very long.
Thousands of volcanoes are on the bottom of the sea. Sometimes volcanoes can form islands. The lava turns to igneous rock and makes more good soil and land.
Sometimes volcanoes can be helpful. Ash from volcanoes make good soil so plants can grow healthy. Some rocks from volcanoes can form pieces to build houses
Volcanoes can be harmful. Volcanoes hurt people and KILL people. Lava can kill people too. A Volcano can wipe out a city. In 1902 one of Mont Pelee's volcanoes ERUPTED and wiped out city called Saint Pierre. Volcanoes can also change weather. In 1815 Mount Tambora erupted covering the sky with ash clouds for three hundred miles making it colder than normal and making it harder for people to breath.
Where Some Volcanoes Are
There are thousands of volcanoes around the world. Volcanoes are mostly in the Pacific Ocean on borders between tectonic plates in the ring of fire. There is a volcano on mars!