Modern humans have never witnessed a supervolcano eruption. The planet's most recent supervolcano eruption happened about 74,000 years ago in Indonesia.
At Yellowstone, the Grand Prismatic Spring is the largest hot spring in the United States and the third largest in the world.
A volcanic bomb is a lava fragment that is rounded as it flies through the air.
Mount Etna has one of the longest documented histories of activity on Earth. Humans have been noting its eruptions since 1500 B.C.
Sicily's Mount Etna is Italy's most active volcano.
Large and in charge
Mount Etna is the largest active volcano in Europe.
The Yellowstone National Park area overlies the Yellowstone Caldera, an active supervolcano that last erupted many thousands of years ago but still fuels some 10,000 geothermal features (geysers and hot springs) that's half of the world's total.
Phreatic eruptions are stream-driven eruptions that happen when water beneath or above the ground is heated up, potentially causing it to boil and "flash to steam," creating an explosion, according to the U.S. Geological Survey.
Ring of fire
The infamous Pacific Ring of Fire is a string of volcanoes strewn around the perimeter of the Pacific Ocean that produces some of the world's most dramatic and dangerous eruptions. This perimeter is where many plates subduct beneath one another.
Three-quarters of the world
The Pacific Ring of Fire is home to 452 volcanoes that's 75 percent of the world's active and dormant volcanoes.