Types of volcanoes explained: from cinder cones to supervolcanoes
Not every volcano looks like Mount Fuji. The popular image of a sharp conical mountain is only one of several shapes that volcanoes take, and those shapes carry information about magma composition, eruption style, and risk. Here is a tour of the main types, with examples and visual cues for recognising them in the field.
Stratovolcanoes
The classic textbook volcano. Steep, layered cones built from alternating ash, lava and pyroclastic flows. Common at subduction zones. Examples: Fuji, Vesuvius, St. Helens, Cotopaxi. Eruptions are typically explosive because the magma is sticky andesite or dacite. Recognise them by the symmetric profile and the long line of similar peaks along a plate boundary.
Shield volcanoes
Wide, gently sloping volcanoes built almost entirely from runny basaltic lava that travels far before solidifying. Hawaii is the type locality. Mauna Loa, the largest, is fifty times the volume of Mount Everest measured from its base on the sea floor. Eruptions are usually non-explosive and visitable. Recognise them by the very low slope angle and broad footprint.
Caldera volcanoes
Volcanoes that have collapsed in on themselves after a large eruption emptied the magma chamber. The depression — the caldera — can be tens of kilometres across. Examples: Yellowstone, Aso, Santorini, Toba. Often filled with water (lake) or sea. The volcano is not destroyed; it usually rebuilds new cones inside the caldera.
Lava domes
Steep, often nearly hemispherical mounds of viscous lava that extrudes too slowly to flow far. Common as part of stratovolcano craters. Mount St. Helens' modern dome is the standard illustration. Lava domes are unstable: they collapse, sometimes explosively, producing pyroclastic flows.
Cinder cones (scoria cones)
Small, steep cones built of loose pyroclastic fragments thrown out of a single vent. Most are monogenetic — they erupt once and shut down. Tens of thousands worldwide. Paricutín in Mexico is the famous example, born in a cornfield in 1943. Recognise them by the regular conical shape, dark colour and small size.
Tuff cones and maars
Volcanoes formed when rising magma encounters water near the surface. The interaction is explosive, producing a low cone or crater rather than a tall mountain. Maars are craters with no significant rim, often filled with water. Examples: the Eifel maars in Germany, Diamond Head on Oahu.
Lava plateaus and flood basalts
Not classic volcanoes but vast flat regions built by enormous basaltic flows. The Columbia River Basalts in the United States and the Deccan Traps in India are continental-scale examples. Such flood basalts are linked to mass extinctions in deep time.
Submarine volcanoes
Most of the Earth's volcanism is under water, along mid-ocean ridges and in island chains. Submarine volcanoes can grow into seamounts and eventually break the surface — Surtsey in Iceland emerged that way in the 1960s. Eruptions are visible mostly to satellites, fishing fleets and bathymetric surveys.
Supervolcanoes
Not a strict scientific category but a useful informal one: volcanoes capable of erupting more than 1,000 cubic kilometres of material in a single event. Yellowstone, Toba and Taupo are canonical examples. Their eruptions are rare on human timescales and continent-altering when they occur.
Mud volcanoes
Not magmatic at all, but worth knowing. Mud volcanoes form when warm, gas-charged subsurface mud rises through sediment, often above oil and gas fields. The Makran coast of Iran has dozens. They look like volcanoes, behave like volcanoes, but are a fundamentally different geological phenomenon.
How to read a volcano
The shape of a volcano often tells you most of what you need to know about it. A steep cone implies sticky magma and explosive risk. A broad shield implies runny lava and less explosive behaviour. A caldera implies past collapse and the possibility of future enormous events. A line of small cones implies repeated short-lived eruptions.
See them on the map
Open the map, filter by region, and look for the characteristic patterns: lines of stratovolcanoes along subduction arcs, clusters of cinder cones in volcanic fields, broad shields offshore in Hawaii, calderas reading as round depressions in the landscape.