Geologic interpretation of images begins with the identification of lineaments, “regional linear features caused by linear arrangement of regional morphological features such as streams, escarpments, and mountain ranges and tonal features that in many areas are the surface expressions of fractures or fault zones.”[i] The emphasis in this section is on geologic structures and landforms, both of which can be easily identified on air photographs and other images.
The sequence followed here is that often found in geomorphology books. Geologic structures and structurally controlled landforms are illustrated first, followed by images of mass wasting and of the results of the agents of erosion—running water, ground water, ice, wind and the sea. The meandering rivers of southern Manitoba are excellent examples of that river form. Several of them have deposited deltas into lakes. The effects of ground water are less easily illustrated, but examples of spring sapping and artesian erosion exist in the south. As all of Manitoba was covered by ice during the latest glaciation, examples of glacial erosion, and especially of glacial deposition, are widespread. Equally impressive are the suite of landforms created by the large glacial lakes that appeared as the ice melted. Glacial spillways, glacial lake deltas, strandlines and flat lake floors are found in many places. Wind action has created dunes on some of the deltas and on glacial outwash deposits. The Hudson Bay coast is rising as a result of isostatic rebound, recovery from the weight of the ice. One result is the existence of strandlines many metres above the level at which they were created. Finally Manitoba’s great lakes are large enough to illustrate many of the landforms normally associated with sea coasts.
[i] Lillesand, T. M. and Kiefer, R. W. Remote Sensing and Image Interpretation (Third Edition). New York: Wiley, 1994, 179.
3.76: The Assiniboine Spillway South of Miniota
This photograph was taken from a greater height than that in figure 3.75. Hence a longer stretch—about 10 miles (16 km)—of the spillway is seen crossing the area from northwest to southeast 1. In this area the spillway is 1 to 1.25 miles (1.6 to 2.0 km) across, slightly wider where Golden Creek 2 enters from the northeast. The Assiniboine River 3 meanders freely across the spillway floor, but in one reach it hugs the south side of the valley for over two miles (3.2 km) 4. Here a dike has been built along the north bank 5 to protect the land to the north from flooding. This land is used for agriculture, and it is noticeable that three abandoned channels have dried out 6. In other places recently abandoned channels are partly water-filled 7. The valley walls are almost 250 feet (76 m) high and as in figure 3.75 the southern and western side is heavily wooded 8, whereas the south and west facing slopes have only patchy woodland 9. Two small creek valleys break the continuity of the southern side 10, while four valleys including that of Golden Creek 2 as well as Drydens Ravine 11 dissect the opposite side. The spillway is sliced across ground moraine that can be seen to the southwest and northeast. In the southwest there is a northwest/southeast lineation 12 that is missing from the northeast where the topography is very irregular with numerous intermittent lakes 13.
Most of the land on the spillway floor is used for agriculture with just a few wooded areas left 14. On either side of the spillway most land has been cleared for agriculture with some land in the process of being cleared 15. The imprint of the DLS system is obvious. Roads follow section lines except where they cross the spillway 16 and creek valleys 17. PTH 83 18 is the only major north/south route way whereas several transport lines cross the area in a general east/west direction. PTH 24 19 is very prominent and both CN 20 and CP 21 railway lines cross the area, crossing each other near the small settlement of Quadra 22. Another east/west line—light-toned on the photo—is a gas pipeline, visible because of the disturbance of the black soils during construction 23. The village of Miniota 24 is located at the junction of PTH 24 and PTH 83.
Figure 3.76: The Assiniboine Spillway South of Miniota
Vertical air photograph: A21748-108
Flight height: 24,700 feet a.s.l.; camera focal length: 85.611 mm
Date: July 27, 1970
Scale: 1:82,300 (approx.)
Location: Townships 12, 13, and 14; Ranges 25, 26, and 27 WI