A volcano is an opening in Earth's surface where molten rock, ash, and gases burst out from deep underground. When pressure builds up beneath the surface, hot liquid rock called magma forces its way up and erupts as lava, sometimes shooting rock fragments and ash miles into the sky.

Volcanoes form where Earth's crust is thin or cracked, often along the edges of massive underground plates. Some volcanoes erupt explosively, like Mount St. Helens in 1980, which blew its top off in a catastrophic explosion. Others, like the volcanoes in Hawaii, ooze lava more steadily, creating rivers of glowing orange rock that can flow for miles.

While volcanic eruptions can be destructive, they've also shaped our world in remarkable ways. Volcanic soil becomes incredibly fertile for farming. The Hawaiian Islands themselves are actually the tops of enormous underwater volcanoes. Ancient Romans built entire cities near volcanoes despite the danger because the land was so productive.

Scientists called volcanologists study volcanoes to predict eruptions and keep people safe. They measure tremors, watch for gas releases, and monitor changes in the mountain's shape. Some volcanoes are dormant (sleeping but could wake up), while others are extinct (permanently inactive). A volcano that erupts regularly is called active.