Yellowstone National Park is currently a placid and majestic landscape, but lurking beneath the surface is a supervolcano that wreaks widespread havoc whenever it awakens. Scientists have long expected it would take centuries for Yellowstone to transition to an active volcano again, but now they’re cutting that timeline down to as little as a few decades.

The Yellowstone Caldera has erupted three times over the last 2.1 million years. It would have been a perilous time to be in North America during those eruptions, but geologists note that many of the park’s features like geysers and hot springs are thanks to the underlying volcanic activity. To take the park from calm landscape to fiery hellscape, the caldera needs to fill with magma. Once the pressure reaches a certain point, the volcano comes roaring back to life.

The timeline for that resurgence is up for debate. A study of Yellowstone Caldera in 2013 assuaged some fears when it found that the magma chamber beneath the park was about two and a half times larger than previously thought. Since the chamber is drained after each eruption, it should take a rather long time to fill it up. Or so you would think.

A new analysis of the caldera suggests that the magma chamber could rapidly refresh. In this case, “rapidly” means several decades, but that’s a geological blink of the eye. Researchers from Arizona State University sampled fossilized ash deposits from the last eruption 631,000 years ago. This eruption spewed 240 cubic miles of rock and ash into the air and left a 40-mile hole in the landscape. That depression now makes up most of the park.

Crystallized formations in the ash allowed the team to track the increase in temperature over time. They expected to see the process take place over hundreds or thousands of years. However, the increase in temperature seems to have happened very quickly. That means magma could surge quickly into the chamber and lead to an eruption.

That’s the bad news. The good news is that Yellowstone is one of the most closely watched geological systems on Earth. A network of ground sensors and satellites keep tabs on the caldera for signs of activity. Stopping an eruption is currently outside our power, but we could at least work to mitigate the potential damage. Although, there are some who would like to head off the next eruption before it ever happens.