Antarctica’s ice sheet hides a massive system of volcanoes, one that is comparable to volcanic regions in East Africa and western North America, according to a new study, which found 91 previously undiscovered volcanoes, some over 12,600 feet tall.

Volcanoes aren’t completely unknown in Antarctica: some poke up through the existing ice sheet, while other studies have examined exposed outcrops. However, ice blankets the surface of the continent, making it impossible to directly study the underlying geology. A team of researchers from the University of Edinburgh’s School of GeoSciences examined a digital elevation model called Bedmap 2 DEM. That survey created a surface elevation model using radar imaging, which the team examined, looking for volcanic structures.

The team created a series of criteria for identifying probable volcano cones: a mound that has a certain length vs. width ratio and which has an elevations of more than 328 feet (100 meters), which were then examined from multiple angles to discern its shape. From that data, the team put together a five-point criteria to gauge how confident they were that each structure was a volcano.

The study resulted in the discovery of 178 cone-shaped structures in a region that researchers named the West Antarctic Rift System. Of those structures, researchers found that 138 are likely volcanoes, based on their confidence criteria. The identified volcanoes range from 328 feet (100 meters) to just over 12600 feet (3850 meters) in height, with cones that range from about two miles to just under 40 miles in dimeter. Of those volcanoes, 91 had not been previously been identified, and the study’s authors explain that the density of the volcanoes in the WARS is approximately one volcano per 4800 square miles. This puts the region in the company of other massive volcanic regions around the world, such as the East African Rift, which has around one volcano per 4500 square miles.

The results could have major implications for our understanding of the region and the massive ice sheet that covers it. The study’s authors explain that they aren’t able to determine if any of the newly-discovered volcanoes are active, but note that their survey should be able to help fuel future studies to help determine that. They also don’t believe that volcanic activity has played a role in the present retreat of the ice sheet.

However, they do believe that the presence of volcanoes in the area will play a role in how quickly the sheet retreats in the future. They cite studies of glaciers in Iceland, which were helped along by the heat by underlying volcanic activity. There’s other implications as well: the team says that there’s evidence that the removal of a kilometers-thick ice sheet can lead to an increase in volcanism, something that’s also been seen in Iceland.

On the other hand, the presence of the volcano cones themselves could also help slow glacial movement: ice flows downward as long as it’s easy for it to do so, but rough underlying terrain can help impede this movement. The team explains that they found a number of cones in the area that “could represent some of the most influential pinning points for past and future ice retreat.”

Ultimately, the surface of Antarctica hidden by its massive ice sheet is home to one of the largest volcanic regions on Earth, the existence of which could have a profound impact on the future of the region, which is already quickly changing.