The Gruben glacier in Switzerland has a core of glacier ice covered by debris. Over the years, the debris has preserved the glacier core, which is slowly melting. The glacier ice has been shrinking since around 1850, causing surface lakes and ice exposures. The glacier's volume is decreasing due to melting, leading to slower movement of the rock glacier. As the climate warms, more glacier ice is expected to be exposed. This challenges the idea that rock glaciers are solely formed by permafrost.