A deep, tensional crevasse formed around the head of a cirque glacier. The crevasse forms as ice falls away downslope. Often, a sequence of bergschrunds forms. Johnson’s bergschrund hypothesis (1904, J. Geol. 12) explained headwall retreat by vigorous frost weathering in a narrow zone; Lewis (1940) Geog. Rev. 30 suggested that meltwater forced its way down far below the bergschrund, explaining the great height of some cirque headwalls. For the limitations of bergschrund theory, see D. R. Stoddart (1997).