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Chapter 3: Geologic Structure and Landforms

3.46: Glacial Grooving in the Interlake and Westlake Regions

This is a LANDSAT I colour composite made using bands 4 (0.5-0.6 micrometres: green), 5 (0.6-0.7 micrometres: red), and 7 (0.8-1.1 micometres: infrared); consequently infrared radiation is represented in addition to some parts of the visible section of the electromagnetic spectrum. The data was recorded on April 23, 1974 before the leaf-on stage of deciduous trees, but coniferous trees were reflecting infrared radiation producing an orange tinge over much of the image.

At this date Riding Mountain 1 is still snow covered, and most of the water bodies are still ice covered with a surface layer of snow and consequently appear white on the image. Within Riding Mountain National Park, Whirlpool Lake 2, Clear Lake 3, Shoal Lake 4, Lake Audy 5, and Whitewater Lake 6 can be seen. North and east of the park are Dauphin Lake 7, Lake Mantitoba 8, Dog Lake 9, Ebb and Flow Lake 10, Lonely Lake 11, Portage Bay (part of Lake Manitoba) 12, Lake St. Martin 13, Sturgeon Bay (part of Lake Winnipeg) 14, Spence Lake 15, Long Island Bay 16, and Sagemace Bay 17 (part of Lake Winnipegosis 18); and Waterhen Lake 19. All these water bodies are ice and snow-covered, but there are some areas of open water, dark blue in colour, for example, Jackfish Lake 20, the south end of Dauphin Lake 21, and Pineimuta Lake 22. Also there is open water where there is a strong current between water bodies; for example, at the Narrows on Lake Manitoba 23 and just to the south of that 24, south of Peonan Point 25, at Crane Narrows 26, at the Narrows on Lake St. Martin 27, and where the Fairford River flows into Portage Bay 28.

There is also a lot of open water—dark blue—east of Lake Winnipegosis and Waterhen Lake 29 and west of Lake Manitoba 30. The water lies in north/south trending grooves, mapped as intermittent water bodies and marshy areas on topographic maps. The grooves were etched into the Devonian bedrock of the area by southward moving ice, the ice exploiting minor variations in resistance to erosion. These grooves should not be confused with similar features trending generally southeast/northwest along the east and north side of Riding Mountain 31 and Duck Mountain 32. These are Lake Agassiz strandlines deposited after ice had retreated from this area.

In addition to the natural features observed, some land has been cleared for agriculture, for example, at the base of the Riding Mountain escarpment 33, around Dauphin Lake 34, and in the fertile Swan River Valley 35. In these areas the characteristic checkerboard pattern of the DLS is seen.

Figure 3.46: Glacial Grooving in the Interlake and Westlake Regions

Figure 3.46: Glacial Grooving in the Interlake and Westlake Regions

Figure 3.46

Landsat I image

Date: April 23, 1974

This is a colour composite of bands 4—wavelength 0.5-0.6 micrometres (green), 5—wavelength 0.6-0.7 micrometres (red), and 7—wavelength 0.8-1.1 micrometres (infrared)

Scale: 1:1,000,000 (approx.)