Scientists are warning that a massive volcanic eruption could happen way sooner than we think. Some of the world’s most powerful volcanoes are showing signs of waking up, and experts are keeping a very close eye on them. Small earthquakes, rising magma, and gas emissions are all pointing to something big brewing underground.

If one of these giants erupts, it could affect everything—flights, weather, and even global temperatures. The good news? Scientists are working hard to predict when and where it might happen.

The bad news? Nature doesn’t always play by the rules.