| Résumé | High-speed video (1000 frames/s) was used to record the propagation of fractures in a 1.7 m thick freshwater ice sheet in Tuktoyaktuk Harbor, N.W.T. The fractures were induced by an indentor operating in a 0.33 m deep trench in the ice where it pushed against the upper 0.2 m edge of the sheet. Most fractures were planar horizontal shear cracks. Some vertically-oriented horizontally-propagating fractures were also observed. Pre-existing cracks in the ice had a considerable effect on the shape and propagation characteristics of the induced cracks. The fractures propagated intermittently, where the average velocity as a fracture progressed through several jump episodes was low (in the 0-50 m/s range), whereas the velocity measured at the brief jumps was in the 0-550 m/s range. |
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