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Surficial Geology
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Glacial Erosion of Bedrock and Ice Flow History in the Kivalliq Region
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Glacial Erosion of Bedrock and Ice Flow History in the Kivalliq Region, Nunavut, Canada
Glacial Flow Indicators
Glacial flow indicators include striations, grooves, rat tails, crescentic gouges and fractures, chattermarks, roches moutonnées, bedrock steps and crag-and-tails. These features are thought to have been formed by the scouring action of sliding basal ice. They primarily reflect late glacial ice flow patterns, although as shown in the next section, cross-cutting relations among these features indicate that older features can be preserved.
| Glacial Flow Indicator | Photo Description |
|---|---|
| Approximately 15 km NW of Imikula Lake in the Ferguson Lake map area, north-south trending delicate striae are preserved on the lee-side (SE) of a NE-SW trending ridge of mafic volcanic rocks. The northward sense of movement is derived from mini whaleback forms consisting of rounded and striated bedrock at the upflow end and a gentle, striated slope at the downflow end. | |
| Fine striations occur in linear depressions enhanced by differential glacial erosion of quartz veins and softer mafic volcanic rocks of the Rankin Inlet greenstone belt. The site is exposed at low tide on a small island in Rankin Inlet. | |
| A rat tail or mini crag-and-tail feature is a streamlined ridge consisting of a "crag" of hard rock (here a felsic volcanic pillow) at the stoss end and a lower, elongated, gentle slope, forming a "tail" on the downflow end of the softer rock (here mafic volcanic rock). This rat tail indicates ice flow towards the SE, along the Hudson Bay coast in the Rankin Inlet area. | |
| Crescentic gouges are fracture cracks resulting from the removal of rock flakes by subglacial quarrying. Their "horns" point up-ice. The fracture plane dips down-ice and terminates with a steep or near vertical face. | |
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larger image [JPEG, 46.5 kb, 632 X 399, notice] |
Elongated bedrock outcrops striated and polished on the stoss side and fractured, quarried, or plucked on the lee side are commonly observed in the Kivalliq Region. These features parallel the dominant and generally most recent ice flow event towards the SE. |
| Quarrying and plucking encouraged by the presence of up-ice dipping joints in granite between Chesterfield Inlet and Gibson Lake, results in the formation of extensive areas of bedrock steps. The photo was taken from a helicopter and the scale is estimated. | |
| Crag-and-tail landforms consist of an elongate ridge composed of a bedrock knob (crag) with a tail of sediment (generally till) extending in the downflow direction. In Princess Mary Lake, this feature indicates a NNW ward ice flow direction, that is parallel to striations preserved on the down-ice side of dominant WSW-ward striations and streamlined landforms. This complex ice flow record is preserved in the area of the Keewatin Ice Divide. |
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