An ice-cored mound that develops within the active layer and permafrost of the periglacial zone. These conical mounds can be up to 40 meters high and 600 meters wide. Layers of ice may separate out by percolation of water, or form by the injection of water-charged sediment from below. When a pingo melts, its center collapses, leaving behind a circular 'rampart' of material (a circular ridge with a central basin, often filled with peat). Pingo ramparts have been used to reconstruct the extent of the periglacial zone which developed around the Devesian/Weichselian ice-sheets.