Hawaii's Mauna Loa volcano is awake after a 40-year snooze! Mauna Loa is not the only volcano that might cause trouble, though. Did you know that underneath Yellowstone National Park lies one of the world's largest volcanoes? While Yellowstone is stable right now and hasn't displayed any unusual seismic activity lately, if it were to erupt, the aftermath could be pretty bad. There are around 1,500 active volcanoes on Earth. What would happen if they all erupted at the same time? Learn more about your ad choices. Visit megaphone.fm/adchoices