Bergschrund is a type of crevasse near the back of a cirque. It is a very deep and narrow crack marking the line along which the glacier ice is moving away from the cirque’s back wall. Bergschrund is also called headwall crevasse. It forms when snow and firn compact and pull away from the back wall of a cirque at the head of the glacier.
“The bergschrund crevasse opens in summer near the top of the ne’ve’ field of a cirque, where the head of a glacier is pulled away from the precipitations wall or from the ice adhering to them”. A. Holmes. During winter such irregular crevasses are closed by snow, but in warmer months the snow melts and they are open.