Ice-thrust terrains and glaciotectonic settings in central Alberta

Airphoto analyses, geologic field mapping, and study of borehole logs and surficial topographic maps in ice-thrust terrains in central Alberta suggest that all these techniques are needed to identify ice-thrust terrains that may or may not have topographic expressions.Three geomorphological settings susceptible to glaciotectonic deformation are described as escarpment, valley, and plains settings. The bedrock slopes in the escarpment setting ranged from 19 to 51 m/km. The bedrock slopes in the valley setting ranged from 23 to 32 m/km, and the valley was 8.5 km wide between crests and 4 km at the bottom. The bedrock slopes of the plains setting ranged from 2 to 5 m/km.Ice-thrust features are found in topographic troughs in front of an ice sheet where water bodies were impounded. These proglacial water bodies thawed the permafrost in front of the glacier. The disintegration of proglacial permafrost decreased the resistance of subglacial strata to ice thrusting.Ice-thrust features can be expected in areas where local slopes are inclined upglacier toward the former glacier margin, where proglacial water bodies could be impounded, rather than in areas where slopes inclined downglacier away from the glacier margin, where the existence of a proglacial water body is unlikely.