The most active volcano in the Philippines, called Mayon, is in danger of a major eruption. It’s been spewing ash for two weeks, and, starting this week, it’s started sending out lava as well. The Philippines are in the so-called “ring of fire,” where the tectonic plates mean that earthquakes and volcanos are a fact of life. Still, that doesn’t mean they’re safe. Thousands who live nearby have fled, and the threat level is up to four out of five. (Five means that a major eruption is taking place.) Here’s what’s happening.