A volcano is an opening in the crust where lava, volcanic gases, and ash are expelled onto the earth’s surface. They typically have cone-like shapes with depressions at their centers. There are three main types of volcanoes: shield volcanoes, stratovolcanoes (also known as composite volcanoes), and cinder cones. Apart from these main types, other categories of volcanoes include calderas, lava domes, and fissures. Now, let’s learn a bit more about each of the different types of volcanoes:

Shield Volcanoes

Shield volcanoes are made of layered lava rock from lava flows; wide, with gently sloping sides. They can be very large: up to ~ 10 km (6 mi) tall, when measured from the sea floor.

Examples: Menengai Crater, Mount Wrangell, Mauna Loa & Mauna Kea

Stratovolcanoes (Composite Volcanoes)

Stratovolcanoes are also called composite volcanoes. Their make-up includes layers of volcanic rock fragments and lava rock. You can find stratovolcanoes in areas near subduction zones and may have very explosive eruptions. This type of volcano is fairly steep-sided and medium-sized, about 1,000 – 4,000 m (3,000 – 13,000 ft) tall.

Examples: Mt. Fiji, Mt. Rainier, and Mt. St. Helens

Cinder Cones

Fragmented volcanic rocks (called “pyroclasts”) comprise cinder domes. They appear very steep-sided but relatively small – up to ~ 500 m (~ 1,600 ft) tall. They can occur on the sides of larger volcanoes.

Examples: Hverfjall, Hoodoo Butte, and Sunset Crater

Calderas

A caldera forms when a volcano’s magma chamber collapses. They appear bowl-shaped and some fill with water to create lakes. Some calderas produce severe eruptions. Calderas are 1 km (0.6 mi) wide or greater. They can be huge, like the Yellowstone Caldera, a super volcano.

Examples: Crater Lake, Krakatoa, and Eyjafjallajökull

Lava Domes

Lava rock; round or spire-shaped. Interestingly, they form when viscous (thick) lava reaches the surface and piles up because it cools faster than it can flow away. Lava domes are like corks in bottles and can erupt violently. Although powerful, lava domes are relatively small; they may be found on top of larger volcanoes.

Examples: Lassen Peak, Chaitén, and Novarupta

Fissures

A fissure is an elongated vent rather than a central vent; they are found on the ocean floor at divergent boundaries. Additionally, fissures can occur on land.

The length of fissures varies. The longest fissure eruption in recorded history was the Laki fissure in Iceland in the 18th century. It was ~ 25 km (~ 16 mi) long. In contrast, very small fissures are sometimes on the sides of larger volcanoes.

Examples: Laki, Hertali, and Alu

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References and Further Reading

1. British Geological Survey (n.d.). Types of Volcano. Available: https://www.bgs.ac.uk/discovering-geology/earth-hazards/volcanoes/how-volcanoes-form/
2. C.C. Plummer, D.H. Carlson, and L. Hammersley (2019). Physical Geology. McGraw-Hill Education. (Chapters 4)
3. National Park Service (n.d.) Types of Volcanoes. Available: https://www.nps.gov/subjects/volcanoes/types-of-volcanoes.htm
4. National Park Service (n.d.). Volcanic Eruptions. Available: https://www.nps.gov/subjects/volcanoes/volcanic-eruptions.htm
5. Volcano World (n.d.). Laki, Iceland – 1783. Oregon State University. Available: https://volcano.oregonstate.edu/laki-iceland-1783
6. Yellowstone Volcano Observatory (2022). Active, Dormant, and Extinct: Clarifying confusing classifications. U.S. Geological Survey news. Available: https://www.usgs.gov/observatories/yvo/news/active-dormant-and-extinct-clarifying-confusing-classifications

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