Types of Volcanoes

Study Notes

Volcanoes are classified based on their shape and the type of eruption they produce. Shape is determined by the viscosity (resistance to flow) of the magma and the nature of the eruptions.
Shield volcanoes are broad, gently sloping volcanoes built from fluid, basaltic lava flows. They are characterized by massive size and frequent, less explosive eruptions. Eruptions are relatively quiet.
Cinder cones are small, steep-sided volcanoes built from loose pyroclastic fragments (cinders) ejected from a single vent. They are characterized by short-lived eruptive activity and fairly simple structure.
Composite volcanoes (stratovolcanoes) are large, cone-shaped volcanoes composed of alternating layers of lava flows and pyroclastic materials. They are characterized by explosive eruptions of viscous andesitic magma, often accompanied by significant pyroclastic flows.
Calderas are large, roughly circular depressions formed by the collapse of a volcano's summit following a massive eruption. They can be vast and represent the sites of exceptionally powerful volcanic events.
Lava domes are bulbous, steep-sided structures formed by highly viscous magma that erupts slowly and extrudes rather than flows.
Subglacial volcanoes emerge and erupt beneath glacial ice. Their eruptions can create distinctive landforms and often involve the interaction of magma with ice.

Effusive eruptions are characterized by the outpouring of fluid lava. Magma with a low viscosity flows easily, creating lava flows that spread over large areas. Lava domes are a common feature of effusive eruptions.
Explosive eruptions are characterized by the rapid ejection of fragmented volcanic material (pyroclastic material) into the atmosphere. Highly viscous magma produces explosive eruptions. These eruptions create ash clouds, pyroclastic flows, and significant explosions. Different types of explosive eruptions vary in intensity and magnitude.