At least 1,299 episodes of unrest have occurred at 138 calderas greater than 5 km in diameter during historical time.
In a typical year some form of unrest (earthquakes, ground deformation, change in fumarole activity, or eruptions) occurs at about 18 large calderas worldwide, and eruptions occur within or near at least five of them.
The largest eruption of the 20th century from the Novarupta vent, in the Valley of 10,000 Smokes of Alaska, ejected about 12 cubic kilometers of magma and resulted in the formation of a caldera 3 km across. Amazingly, the caldera collapse didn’t occur at the eruption vent, but 10 km away at Katmai, a stratovolcano! Apparently magma drained away from Katmai’s magma reservoir to Novarupta’s erupting vent.
Yellowstone National Park consists of three enormous calderas that erupted about 2, 1.2, and 0.6 million years ago. The most recent caldera is 45 km across and 75 km long!
Caldera-forming eruptions are the largest eruptions on Earth. For example, the Fish Canyon eruption in southwestern Colorado about 28 million years ago erupted more than 5,000 cubic kilometers of magma from the La Garita caldera. That’s enough magma to bury the entire state of California to a depth of nearly 12 meters! Source: USGS