Water can also accumulate in a bedrock depression below the ice dome, such as a crater. A water cupola forms if the glacier bed is flat and the surface ice has a central depression, thus forming a relatively low-pressure area in the center of the ice. This low-pressure region under the ice then fills with water. Englacial pockets of water form when a crevasse has been filled with water and the crevasse then closes, thus trapping pockets of water with in the ice. These pockets do not store large quantities of water.
Supraglacial lakes form early in the melt season before the englacial system opens up.
On cold based ice the lakes can persist during the ablation season without draining away. Debris laden glaciers, because of differences in albedo, lead to differential melting. This differential melting can lead to sinkholes, or water filled hollows. Finally ice cauldrons form from large amounts of geothermal heat rising through the ice and melting the surface of the glacier. Supraglacial meltwater storage on a debris laden glacier Mt.