Volcanoes that have produced exceedingly voluminous pyroclastic eruptions and formed large calderas in the past 2 million years include Yellowstone in northwest Wyoming, Long Valley in eastern California, Toba in Indonesia, and Taupo in New Zealand.

While there are approximately 20 known supervolcanoes globally, the "Big 4" most frequently discussed in 2026 due to their activity and proximity to population centers are: Yellowstone (USA), located primarily in Wyoming; Lake Toba (Indonesia) on the island of Sumatra; Taupō (New Zealand) on the North Island; and Long Valley Caldera (USA) in eastern California. Each of these is a "caldera" volcano, meaning they don't look like traditional cones but rather massive depressions in the earth. In 2026, the Campi Flegrei in Italy is also heavily monitored as a potential fifth major threat. These volcanoes are defined by their ability to produce an "VEI-8" eruption, ejecting more than 1,000 cubic kilometers of material, which would be enough to trigger a volcanic winter and global climate shift lasting decades.