Types of Volcanoes: Shield, Strato, Cinder Cone & More

Types of volcanoes at a glance

Volcanoes are classified mainly by shape and how they are built. Shape, in turn, records the kind of magma a volcano erupts: runny, low-silica basalt spreads out into wide shields and fissure flows, while sticky, silica-rich andesite, dacite and rhyolite pile up into steep cones and domes or blast out in caldera-forming eruptions. (For the chemistry behind this, see Volcanology 101.)

Shield volcanoes

Shield volcanoes are built from thousands of thin, fluid basaltic lava flows that travel far before cooling. The result is a broad dome with gentle slopes, often only a few degrees, shaped like a warrior's shield lying on the ground. They form mostly over hotspots and at rifts, where decompression melting produces hot, low-silica magma.

Mauna Loa in Hawaii is the largest active volcano on Earth: it rises about 9 km from the sea floor and its own weight has pressed the ocean crust down beneath it. Its neighbour Kīlauea is one of the most active volcanoes in the world; its 2018 eruption in the lower East Rift Zone destroyed more than 700 homes, a reminder that "gentle" lava flows still destroy property even when they rarely kill people.

Stratovolcanoes (composite volcanoes)

Stratovolcanoes are the classic tall, steep, symmetrical mountains. They are built from alternating layers (strata) of lava flows, ash and pyroclastic debris, which is why they are also called composite volcanoes. Most sit above subduction zones around the Pacific Ring of Fire, where water-rich, sticky andesitic magma traps gas.

That makes them the most dangerous common type. Mount Fuji last erupted in 1707. Vesuvius buried Pompeii and Herculaneum in 79 CE and last erupted in 1944. Mount St. Helens lost about 400 m of its summit in the 1980 lateral blast. Etna on Sicily is a large, complex stratovolcano that erupts often, mostly with lava fountains and flows. Typical hazards are pyroclastic flows, lahars and ashfall; see eruption types for the styles involved.

Cinder and scoria cones

Cinder cones (also called scoria cones) are the simplest volcanoes: steep piles of gas-bubbly lava fragments thrown from a single vent that fall back around it. They are usually less than a few hundred metres high, often erupt only once, and commonly dot the flanks of larger volcanoes or form fields of many cones.

The famous example is Parícutin in Mexico, which opened in a farmer's cornfield in February 1943 and grew to 424 m before activity stopped in 1952. Scientists could watch an entire volcano's life cycle from birth to extinction.

Lava domes

When lava is too viscous to flow far, it piles up over the vent as a lava dome. Domes grow slowly, but their steep sides can collapse and send out deadly pyroclastic flows (block-and-ash flows). At Unzen in Japan, dome growth between 1990 and 1995 produced thousands of such flows; one on 3 June 1991 killed 43 people, including volcanologists Katia and Maurice Krafft and Harry Glicken. Inside the crater of Mount St. Helens, new domes grew in 1980–1986 and again in 2004–2008.

Calderas

A caldera is a large basin that forms when a volcano's magma chamber empties so quickly during a huge eruption that the roof collapses. Calderas can be tens of kilometres wide and may later fill with lakes or the sea.

• Yellowstone (USA): its most recent caldera-forming eruption was about 631,000 years ago.
• Campi Flegrei (Italy): a restless caldera beneath the suburbs of Naples, where the ground has been rising and falling (bradyseism) for decades.
• Santorini (Greece): the Late Bronze Age "Minoan" eruption reshaped the island ring around a flooded caldera.
• Krakatau (Indonesia): the 1883 eruption collapsed the island and triggered tsunamis that killed about 36,000 people. Anak Krakatau ("child of Krakatau") has been growing in the caldera since 1927.

Fissure vents

Not every eruption comes from a central crater. At fissure vents, basaltic magma escapes along a long crack in the ground, often as a "curtain of fire" of lava fountains. Over time this builds low ridges and rows of small spatter cones rather than a single mountain. Repeated fissure eruptions over millions of years created the vast flood basalt provinces such as India's Deccan Traps.

Iceland, which sits on the Mid-Atlantic Ridge, is the best place to see them. The Laki fissure (1783–1784) erupted for eight months; its gas and the famine that followed killed roughly a fifth of Iceland's population and affected weather across Europe. Since December 2023, a series of fissure eruptions along the Sundhnúkur crater row on the Reykjanes Peninsula has repeatedly threatened the town of Grindavík.

Submarine volcanoes and seamounts

Most of Earth's volcanism is hidden underwater, along the mid-ocean ridges where new ocean crust forms. Under the pressure of deep water, lava erupts quietly as rounded pillow lavas. Isolated underwater volcanoes are called seamounts.

Axial Seamount, about 480 km off the coast of Oregon, is one of the best-monitored volcanoes on the planet, with eruptions in 1998, 2011 and 2015. Because it lies about 1.4 km below the surface and far from land, the USGS describes its eruptions as exciting for science, not hazardous to people. Shallow submarine volcanoes are another story: the Hunga Tonga–Hunga Ha'apai eruption of 15 January 2022 sent a plume into the mesosphere, generated a pressure wave that circled the globe and caused a Pacific-wide tsunami.

Subglacial volcanoes

When a volcano erupts beneath a glacier, the heat melts huge amounts of ice. The meltwater can burst out as a sudden flood called a jökulhlaup, and the interaction of magma with water shatters it into fine ash. Long eruptions under thick ice sheets build steep, flat-topped mountains called tuyas, such as Herðubreið in Iceland.

Grímsvötn, under the Vatnajökull ice cap, is Iceland's most frequently erupting volcano. The 2010 eruption of Eyjafjallajökull was only moderate in size, but its fine, glass-rich ash closed much of European airspace for about a week.

Maars and tuff rings

A maar forms when rising magma meets groundwater. The water flashes to steam and causes violent explosions (phreatomagmatic eruptions) that blast a wide crater cut below the surrounding land, rimmed by a low ring of debris. Many maars later fill with water. A tuff ring is a close relative with a slightly higher rim of cemented ash (tuff).

Europe's textbook examples are the Eifel maars in western Germany, such as the Pulvermaar and the three Daun maars. The Eifel volcanic fields last erupted roughly 11,000 years ago and are still considered potentially active. For more nearby examples, see volcanoes in Europe.

Supervolcanoes

Supervolcano is not a formal shape category. It is a popular term for a volcano that has produced at least one eruption of VEI 8, the top of the Volcanic Explosivity Index, ejecting more than 1,000 km³ of material. Supervolcanoes are almost always large calderas, such as Yellowstone, Toba in Indonesia (about 74,000 years ago) and Taupō in New Zealand (about 26,500 years ago). Such eruptions are extremely rare; most activity at these systems consists of much smaller eruptions, earthquakes and ground movement.

Not real volcanoes: mud volcanoes and sand volcanoes

Some features look like volcanoes but do not involve magma.

• Mud volcanoes form where pressurised gas (often methane) and water push mud up through sediments. They can build cones and even ignite, but the mud is usually cool. Azerbaijan has hundreds of them; Lusi in Java has been erupting mud since 2006.
• Sand volcanoes (sand boils) are small cones of sand formed when water-saturated sand loses its strength during earthquake shaking, a process called liquefaction, and is forced to the surface with the escaping water. They appeared widely in Christchurch, New Zealand, after the 2010–2011 earthquakes. Similar sand boils form behind river dikes during high water.

Active, dormant or extinct?

Volcanoes are also classified by activity, though the terms are looser than many textbooks suggest:

• Active: currently erupting or showing unrest, or, in the Smithsonian Global Volcanism Program's broad sense, having erupted during the Holocene (roughly the last 10,000–12,000 years).
• Dormant: not erupting now but expected to erupt again.
• Extinct: not expected to erupt again, such as Edinburgh's Arthur's Seat.

The problem is that "dormant" has no fixed time limit, and volcanoes can sleep for centuries. Pinatubo in the Philippines had no known eruption for about 500 years before its huge 1991 eruption. That is why the Smithsonian and USGS prefer the Holocene record over the word "dormant." See current examples on our volcano map.

Frequently asked questions