n.
Vent in the crust of the Earth from which molten rock, debris, and steam issue.
Volcanoes are commonly divided into two broad types. Fissure volcanoes occur along fractures in the crust and may extend for many miles; lava is ejected relatively quietly and continuously and forms enormous plains or plateaus of volcanic rock. Central volcanoes have a single vertical lava pipe and tend to develop a conical profile; lava flows from the throat and follows the easiest path downhill. Often in these volcanoes highly viscous lava clogs the throat, causing a pressure buildup that is relieved only by violent explosion and eruption. Such eruptions may completely remove the top of the cone and occasionally also part of its interior.