Volcanoes form when magma rises up through fissures in the Earth's crust caused by movement of tectonic plates. The opening where magma emerges onto the surface is called a vent, and the funnel-shaped depression at the top of an erupting volcano is termed a crater. Active volcanoes frequently erupt, while dormant volcanoes were active in the past but are not currently erupting, though they could become active again. Areas around volcanoes are rich in minerals and some have developed healing hot springs, fertile soil, and tourist attractions.