Underneath Antarctica’s ancient, frozen landscape lies a hidden subglacial valley larger than the Grand Canyon. The recently discovered Antarctic trench, sculpted millions of years ago, is nearly two miles deep and plunges to more than 6,500 feet below sea level. Researchers say the ancient trough could provide invaluable clues about what the West Antarctic ice sheet could look like in a warmer global climate.

British scientists mapped the Ellsworth Subglacial Highlands -- an ancient mountain range buried under Antarctic ice -- using ice-penetrating radar and satellite data. They traversed the Antarctic landscape in snowmobiles and a small aircraft, plotting the buried subglacial terrain piece by piece. Their analysis turned up a valley 1.8 miles deep, 186 miles long and up to 15 miles wide.

“To me, this just goes to demonstrate how little we still know about the surface of our own planet,” lead study author Neil Ross, from Newcastle University, said in a statement. “The discovery and exploration of hidden, previously unknown landscapes is still possible and incredibly exciting, even now.”

How did the mega-canyon form? According to the study, published in the Geological Society of America Bulletin, the canyon was carved when Antarctica broke away from the rest of Earth’s landmass 80 million years ago, creating rifts and chasms. When the detached land reached the South Pole, and temperatures plummeted, glaciers appeared, further scarring Antarctica’s terrain with deep trenches and fissures.

This is the first time scientists have taken a close look at the region under Antarctica’s vast ice sheet. The study offers a new look at the extent and behavior of Antarctica’s ancient ice field.

“While the idea of West Antarctic Ice Sheet growth and decay over the past few million years has been discussed for decades, the precise location where the ice sheet may originate from in growth phases, and decay back to in periods of decay, has not been known,” Martin Siegert, professor of Geosciences at the University of Bristol, said in a statement. “By looking at the topography beneath the ice sheet using a combination of ice-penetrating radio-echo sounding and satellite imagery, we have revealed a region that possesses classic glacial geomorphic landforms, such as u-shaped valleys and cirques, that could only have been formed by a small ice cap, similar to those seen at present in the Canadian and Russian High Arctic. The region uncovered is, therefore, the site of ice sheet genesis in West Antarctica.”

This isn’t the first time scientists have discovered a hidden canyon under ice. Last year, researchers announced the discovery of a 460-mile canyon underneath the Greenland ice sheet.

“A discovery of this nature shows that the Earth has not yet given up all its secrets,” David Vaughan of British Antarctic Survey in Cambridge, who was involved with the Greenland canyon discovery, said in a statement. “A [460-mile] canyon preserved under the ice for millions of years is a breathtaking find in itself, but this research is also important in furthering our understanding of Greenland's past. This area's ice sheet contributes to sea-level rise and this work can help us put current changes in context.”