Instrumental Work on the Nature of Glacier Motion

In an endeavor to decide between viscous flow and crystalline yielding as the basic phenomenon in glacier motion, measurements of the internal shearing in glaciers were made with a self-recording clockwork apparatus. These automatic records show that slipping takes place along definite shearing planes, at times gradually and at other times by distinct jumps. The capacity to withstand a certain amount of growing stress before yielding is indicated. The results speak definitely for the solidity and elastic rigidity of moving glacier ice, and decisively against liquid or viscous flow as the main type of adjustment under stress. Four manifestations of glacier movement are recognized: (1) solid flow by idio-molecular exchange between ice crystals, (2) solid shearing of aggregates of granules, (3) intermittent slip along well-developed thrust-fault planes, and (4) sliding of the whole body of ice over the rock beneath.