A supervolcano is a volcano that has erupted with a volcanic explosivity index (VEI) of 8, the highest level on the scale. This means the amount of material left behind from such an eruption is more than 1,000 cubic kilometers (240 cubic miles).

Supervolcanoes form when magma from the Earth’s mantle rises into the crust but cannot break through it. Pressure builds up in a large magma chamber until the crust can no longer hold it, causing it to break. This can happen at hotspots, such as the Yellowstone Caldera, or at subduction zones, such as the Toba volcano.

Large eruptions from supervolcanoes are often linked to large igneous provinces, which can cover vast areas with lava and volcanic ash. These events can lead to long-term changes in Earth’s climate, such as the start of a small ice age, and may cause many species to become extinct. The most recent VEI-8 eruption was the Oruanui eruption of New Zealand’s Taupō Volcano, which happened about 25,600 years ago.

Terminology

The word "supervolcano" was first used in a scientific discussion about volcanoes in 1949. This idea began with a debate in the early 1900s about the history and features of the Three Sisters volcanic area in Oregon, United States. In 1925, a scientist named Edwin T. Hodge proposed that a very large volcano, which he called Mount Multnomah, had once existed in that region. He thought the several peaks in the Three Sisters area were parts of Mount Multnomah that remained after it was destroyed by powerful volcanic eruptions, similar to what happened to Mount Mazama. In his 1948 book The Ancient Volcanoes of Oregon, a volcanologist named Howel Williams did not mention Mount Multnomah. However, in 1949, another volcanologist, F. M. Byers Jr., wrote a review of the book and used the term "supervolcano" to describe Mount Multnomah.

More than fifty years later, in 2000, the term "supervolcano" became widely known through a BBC television program called Horizon, which described eruptions that release extremely large amounts of volcanic material.

Sometimes, the term "megacaldera" is used to describe supervolcanoes that form large calderas, such as the Blake River Megacaldera Complex in the Abitibi greenstone belt of Ontario and Quebec, Canada.

Although there is no clear minimum size for an eruption to be called a "supervolcano," scientists have identified two types of eruptions that are classified as supervolcanoes: large igneous provinces and massive eruptions.

Large igneous provinces

Large igneous provinces, such as Iceland, the Siberian Traps, Deccan Traps, and the Ontong Java Plateau, are large areas covered with basalt rock formed by massive lava flows. These regions can cover thousands of square kilometers and contain millions of cubic kilometers of lava. In most cases, lava layers form over several million years and release large amounts of gases.

The Réunion hotspot created the Deccan Traps about 66 million years ago, at the same time as the Cretaceous–Paleogene extinction event. Scientists agree that an asteroid impact caused the extinction, but volcanic activity may have added stress to living species before the event. Some researchers suggest that the Chicxulub impact, which occurred near the opposite side of the Earth from the Deccan Traps, might have increased volcanic activity in the region.

The largest flood basalt event, the Siberian Traps, happened around 250 million years ago and occurred during the Permian–Triassic extinction event, the largest mass extinction in Earth’s history. However, it is not certain if the volcanic activity alone caused the extinction.

These lava flows are not explosive, though lava fountains can occur. Many scientists believe Iceland is a large igneous province still forming today. The last major lava flow occurred in 1783–84 from the Laki fissure, a 40 km (25 mi) long crack. During the eruption, about 14 km (3.4 cu mi) of basaltic lava was released (VEI 4).

The Ontong Java Plateau covers about 2,000,000 km (770,000 sq mi). Before the Manihiki and Hikurangi Plateaus separated, the province was at least 50% larger.

Massive explosive eruptions

Volcanic eruptions are grouped based on the volcanic explosivity index (VEI). This scale is logarithmic, meaning that each increase of one number on the VEI represents ten times more erupted material. Eruptions with a VEI of 7 or 8 are extremely powerful. These eruptions often create large, circular calderas instead of volcanic cones because the ground above the magma chamber collapses into the empty space left behind after magma is removed.

According to incomplete data, at least 60 eruptions with a VEI of 8 have been recorded.

Media portrayal

• In September 2006, the show Nova aired an episode titled "Mystery of the Megavolcano," which looked at eruptions that occurred in the past 100,000 years.
• Supervolcano is the name of a British-Canadian television disaster film released in 2005. The film presents a fictional story about a massive volcanic eruption at Yellowstone.
• In the 2009 disaster film 2012, a supereruption at Yellowstone is one of the events that leads to a global disaster.
• The 2025 political thriller Paradise is set after an eruption of a fictional supervolcano in Antarctica and a resulting megatsunami. This event causes the United States federal government and other important people to move to an underground city in Colorado.