According to the Smithsonian Institute's Global Volcanism Program, there are probably about 20 volcanoes erupting right now, and about 550 volcanoes have had historically documented eruptions. A volcano is an opening, or rupture, in the Earth's crust through which molten lava, ash, and gases are ejected. Volcanoes typically form in three different settings. The first is divergent plate boundaries, where tectonic plates are pulling apart from one another, such as the Mid-Atlantic Ocean Ridge. Most of these volcanoes are on the bottom of the ocean floor and are responsible for creating new sea floor. The second location is convergent plate boundaries, where two plates, typically an oceanic and continental plate, are colliding. The volcanoes along the Pacific Ring of Fire are from convergent plate boundaries. The third location is over hotspots, which are typically in the middle of tectonic plates and caused by hot magma rising to the surface. The volcanoes on Hawaii are the result of hotspots.