Volcano

A volcano is an opening in Earth’s crust through which molten rock, gases, ash, and other materials can reach the surface. Below the surface, molten rock is called magma; once it erupts, it is called lava. Volcanoes often form near the boundaries of tectonic plates, especially where one plate sinks beneath another or where plates move apart.

They can also occur above hot spots, where unusually hot material rises from deep within Earth. A volcano may have a central vent, a crater or larger depression, and underground channels that connect the surface to a magma reservoir. Its shape depends on the type of lava, the amount of ash produced, and the history of its eruptions.

Eruptions vary greatly. Some produce relatively quiet flows of lava, while others release ash and gases in explosive events. Volcanic activity can change landscapes, create new land, and contribute to fertile soils as volcanic materials weather. At the same time, eruptions may generate ash clouds, lava flows, falling rocks, or fast-moving mixtures of hot gas and volcanic fragments, creating serious risks for nearby communities.

Scientists monitor volcanoes using earthquakes, ground deformation, gases, and other measurements to detect changes in activity. A volcano is not necessarily erupting simply because it is active; active volcanoes can remain quiet for long periods.