Beneath the rocky slopes of Mount Timpanogos lies far more ice than anyone walking across the surface might suspect. Researchers used gravity measurements to map the buried glacier in 3D and found it is about 83% ice, with enough frozen water to fill 600 Olympic swimming pools. Their findings suggest rock glaciers form as falling debris buries persistent snow and preserves it for thousands of years. Similar formations around the world may collectively store tens of gigatons of hidden water.