It sounds like such a simple question: how many volcanoes are there on the Earth. But it’s actually very complicated, and the true answer is that scientists just don’t know. Some volcanoes are completely unknown, hidden beneath the ocean. Other volcanoes haven’t erupted in a long time, and so scientists don’t know if they’re still active. It also depends on whether you consider a single volcanic vent a volcano, or count an entire volcanic field of volcanoes that connect to a single magma chamber. See how’s it’s complicated to count the number of volcanoes?
The Smithsonian National Museum of Natural History calculates that there are currently about 20 volcanoes actively erupting when you’re reading these words. About 50-70 volcanoes have erupted over the course of the last year, and 160 erupt during a single decade. There are 550 volcanoes that have been active in all recorded history, and geologists have located an additional 1300 volcanoes that have erupted in the last 10,000 years.
So if you add these numbers up, you get about 1500 volcanoes that have erupted in the last 10,000 years.
But most of the actively erupting volcanoes are on the deep sea floor, where nobody was there to measure it. If you assume that 3/4 of all eruptions were underwater volcanoes, you get a total of about 6,000 volcanoes that have erupted worldwide in the last 10,000 years.
So that’s the best estimate of how many many volcanoes there are.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.