These objects are bounded on two sides by the headwall and the sill, and many contain lakes called (*) tarns, which form from icemelt.
The height of these structures was found by Graf to be the strongest predictor of whether they are empty. William White suggested that the primary force acting on these entities is floor deepening rather than headward sapping, noting that cols, or passes, rarely form in them. Parallel to the back wall of one of these there can form a randkluft or a bergschrund. These objects are bounded on two sides by the headwall and the sill, and many contain lakes called (*) tarns, which form from icemelt. The erosion of two of these structures towards each other can form an arête. For 10 points, name these amphitheatre-shaped rock formations that form at the head of valley glaciers.
The height of these structures was found by Graf to be the strongest predictor of whether they are empty.
{cirques} [or {corries}; or {cwms}]