Frank W. Trainer 1973 <p>The orientation of joints in igneous and sedimentary rocks&nbsp;was measured at 21 localities in California, Maine, and New York to&nbsp;investigate the hypothesis that glaciation may open joints in bedrock. A&nbsp;summary of strikes of all joint sets shows the following pattern relative&nbsp;to the direction of glacial advance: two sets, thought to be extension&nbsp;joints, flank the direction of advance and are separated from it by&nbsp;about 10&deg;; two sets, thought to be shear joints, flank the direction of&nbsp;advance by about 40&deg;; and two sets, thought to be release joints, are&nbsp;about 70&deg; to 80&deg; from the direction of advance, or nearly perpendicular&nbsp;to the extension joints. An average of five joint sets, including&nbsp;three or four in this pattern, was found at each locality. The joints are&nbsp;believed to have been opened, in response to stress applied by the&nbsp;moving ice, along preexisting zones of weakness (potential regional&nbsp;joints) in the rock. Some new joints may have formed where no such&nbsp;zone was present near the position required for fracture under the&nbsp;applied stress. Additional investigation of the hypothesis is desirable&nbsp;because of its possible bearing on glacial erosion by quarrying, on&nbsp;interpretation of joint patterns in glaciated regions, and on the nature&nbsp;of aquifers in glaciated bedrock.</p> application/pdf en U.S. Geological Survey Formation of joints in bedrock by moving glacial ice article