Fiery explosions, boiling lava, hot ash spewing everywhere -- total disaster is probably the first thing that comes to mind when you think "volcano." And, yes, that is certainly a possibility. But do you know what’s really going on when a volcano erupts?
About 10 volcanoes are going through some stage of eruption every day. These aren't necessarily big, explosive eruptions, though.
You might think that if 10 volcanoes erupt every day, there should be about 3,650 volcanoes erupting each year. But it's more like 50 or 60. Some volcanoes can be erupting for days, weeks, even months -- it's more of an ongoing thing than a one-day event.
Mount Etna has had regular, documented eruptions for 3,500 years.
In 1815, Mount Tambora erupted, releasing about 100 cubic kilometers of lava. The sulfur it released into the atmosphere decreased world temperatures by about 1 degree Fahrenheit. This caused agricultural problems -- and famine -- all over the world.
Mauna Loa, on the big island of Hawaii, rises 56,000 feet (17,000 meters) from the ocean floor. It's now going through its longest period of inactivity -- it hasn't erupted since 1984.
Lassen Peak, in the Cascade Range of Northern California, had a series of explosive eruptions from 1914 to 1917, the largest of which occurred in 1915. It was the only American volcano besides Mount St. Helens to erupt in the 20th century.
Hawaiian volcanoes tend to have more gradual eruptions with long lava flows, while Strombolian volcanoes erupt very dramatically without much lava.
If it's been 10,000 years since a volcano last erupted, it's considered extinct. If it's not showing any activity but has erupted in 10,000 years, it's called dormant.
About 600,000 people live in the "red zone" around the base of Mount Vesuvius in Italy. And scientists think it could erupt in the near future.
Volcanic ash can reach speeds of 125 mph (200 kph) -- and it can also reach 1,472 degrees Fahrenheit (800 Celsius).