A supervolcano represents a geological event of immense power, capable of drastically reshaping landscapes and influencing global climate patterns. This rare phenomenon is often misunderstood regarding its definition and distribution. To clarify, we examine the scientific criteria that distinguish these sites from ordinary volcanoes and explore the most significant locations where these colossal eruptions have occurred.
Defining a Supervolcano
A supervolcano is defined by the sheer magnitude of its past eruptions, not by a conical mountain peak. Scientists classify these events using the Volcanic Explosivity Index (VEI), a scale measuring the volume of ejected material and the height of the eruption column. To be considered a “super-eruption,” an event must reach VEI 8, the highest level on the index.
This classification requires the volcano to have ejected more than 1,000 cubic kilometers of material, such as ash and pumice, during a single event. This massive expulsion of magma causes the ground above the emptied reservoir to collapse inward, forming a vast, bowl-shaped depression known as a caldera. These massive calderas, sometimes dozens of miles wide, are the primary surface feature of a supervolcano, unlike the familiar mountainous form of stratovolcanoes.
Addressing the Supervolcano Count
The specific number of supervolcanoes is difficult to determine because the term “supervolcano” is a media-popularized label. The scientific community focuses instead on volcanic systems that have produced a VEI 8 “super-eruption.” This leads to a varying count, as no single, fixed list is maintained by global geological surveys.
Estimates of known supervolcanic systems range widely, from as few as six to over sixty. This variation depends on whether ancient events are included or if the focus is only on sites active within the last two million years. The number 20 is a general estimate often cited for the most significant, well-studied systems with evidence of VEI 8 eruptions. The list remains dynamic because ongoing research continues to uncover new evidence of massive past eruptions.
The World’s Major Supervolcanic Systems
The largest and best-known supervolcanic systems are spread across the globe.
Yellowstone Caldera
The Yellowstone Caldera in the northwestern United States lies over a deep mantle plume. Yellowstone has produced three known super-eruptions, with the largest occurring 2.1 million years ago, ejecting an estimated 2,450 cubic kilometers of material. The most recent super-eruption occurred 640,000 years ago, creating the caldera that contains the modern national park.
Lake Toba
In Southeast Asia, Lake Toba in Sumatra, Indonesia, is the world’s largest Quaternary caldera. Toba was the site of an immense VEI 8 eruption approximately 74,000 years ago, considered the largest explosive eruption of the last 25 million years. This event ejected around 2,800 cubic kilometers of material. The eruption was so massive that it caused a volcanic winter, leading to global cooling.
Taupō and La Garita
The Taupō Volcanic Zone on New Zealand’s North Island is home to the most recent VEI 8 event on Earth. The Oruanui eruption at the Taupō volcano occurred about 25,600 years ago, forming the massive caldera now filled by Lake Taupō. In the American Southwest, the La Garita Caldera in Colorado records an even larger event. An eruption approximately 28 million years ago produced up to 5,000 cubic kilometers of ash flow, making it one of the largest single eruptions known.
Predicting and Monitoring Supervolcano Activity
Scientists continuously monitor these massive systems for signs of renewed activity using ground- and satellite-based instruments.
Seismicity
The primary technique is tracking seismicity, which uses seismometer networks to detect swarms of small, shallow earthquakes. These quakes often signal the movement of magma and fluids beneath the surface, providing the earliest indication of volcanic unrest.
Ground Deformation
Another method involves measuring ground deformation, tracking changes in the shape of the land above the magma chamber. Instruments like GPS receivers and tiltmeters detect uplift or subsidence, indicating that magma or pressurized gas is accumulating or withdrawing. Satellite-based Synthetic Aperture Radar (InSAR) also measures ground movement over large areas.
Gas Emissions
Scientists also analyze gas emissions, looking for significant changes in the composition and flux of gases like sulfur dioxide and carbon dioxide, which are released as magma degasses. These monitoring techniques allow for short-term forecasts, but predicting a super-eruption, which operates on geological timescales, remains challenging.