Volcanoes can erupt at any time, but on average between **50 and 60 volcanoes** erupt each year somewhere on Earth (about 1 every week). Some of Earth's volcanoes may actually erupt within a few days or hours of each other.
The largest eruptions come from volcanoes called rhyolite calderas, and these huge eruptions may occur at intervals of **10,000 to 30,000 years**. Yellowstone, the largest caldera in the U.S.A. seems to erupt on average every **600,000 years**.
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