Submarine volcanoes are underwater fissures in the earth's surface from which magma can erupt. They estimated to account for 75% of annual magma output. The vast majority are located near areas of tectonic plate movement, known as mid-ocean ridges. Although most are located in the depths of oceans, some ... exist in shallow water, which can spew material into the air during an eruption. Hydrothermal vents, sites of abundant biological activity, are commonly found near submarine volcanoes.