There are three ways to describe a volcano’s activity; there can be active, dormant, or extinct volcanoes. Active volcanoes have erupted recently. A dormant volcano isn’t erupting right now, but vulcanologists expect it could erupt at any time. Extinct volcanoes haven’t erupted for tens of thousands of years, and aren’t expected to erupt again.
What causes volcanoes to go extinct? Simply put, they’re cut off from their supply of lava. This is where a chamber of magma underneath the surface of the Earth finds its way to the surface through weaknesses in the crust. A good example of this is the hotspot that created the chain of Hawaiian Islands. The tectonic plate carrying the islands is slowly moving, so that volcanoes are cut off from the hotspot underneath. Eventually they go extinct, while the hotspot creates a new volcano further to the East.
Some volcanoes look extinct, but it might just be a long time since they’ve erupted. For example, the Yellowstone Caldera in Yellowstone National Park hasn’t had a violent eruption in about 640,000 years, but scientists think it’s still active. There has been minor activity and lava flows as recently as 10,000 years ago. The region also has regular minor earthquakes and ground is lifting up in some areas, so scientists think that’s it’s still an active volcano.
Volcanoes thought to be extinct have erupted again. For example, Mount Vesuvius erupted famously in AD 79, destroying the towns of Herculaneum and Pompeii. And the Soufriere Hills volcano on the island of Montserrat resumed activity in 1995.
Other volcanoes are clearly extinct, with only the heavily eroded lava plug remaining.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.