It was a surprise when Fourpeaked Mountain, 200 miles southwest of Anchorage, Alaska, erupted in September 2006. It had been quiet since before 8000 BC, and volcanoes which haven't erupted in the past 10,000 years are considered extinct -- and extinct volcanoes are not expected to have a lava supply. Similarly, in 1955, Mount Bezymianny, on Russia’s Kamchatka Peninsula, unleashed the largest single volcanic eruption of the 20th century, and spewed ash for more than a year -- but it had been considered a long-extinct volcano right up until then.
Volcanic eruptions can kill thousands, reshape islands and continents and even affect global weather with their ash clouds. That red sunset you love so much? Thank volcanic ash in the atmosphere!
Right now there are at least 1,900 active volcanoes, around the world, most sitting on top or near the edges of the Earth's tectonic plates, spewing gas, magma (lava), and ash when they erupt. There are three types of volcanic activity: active, dormant, or extinct. And scientists admit can sometimes be difficult to tell the difference between a volcano that's extinct and one that's just resting (sleeping volcanoes are called "dormant").
It's true you can't always tell a book by its cover ... but can you name a volcano by its picture?