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.
This image was obtained from Landsat I using the Multispectral Scanner (MSS) sensor, recording band 7 (0.7-0.8 mm—infrared). The sensor at a nominal altitude of 900 km (559 miles) covers a large part of southwest Manitoba and southeast Saskatchewan. At the time, December 19, 1973, most of the surface was snow covered and appears white on the image, but tree and scrub covered areas appear dark. In the north is Riding Mountain National Park 1 with a sharp boundary reflecting the difference between natural vegetation in the park and land cleared for agriculture outside it. In the south is a parkland area (woodland and grass) surrounding Oak Lake 2 and in the southeast the wooded area of Moose Mountain 3 in Saskatchewan.
At this date, close to the winter solstice, the sun is low in the sky even at noon and this image was obtained well before noon. One result is that topographic features throw prominent shadows, so that in this image spillways and meltwater channels show up prominently. This is particularly true where they trend west/east, the best example being the Qu’Appelle Valley 4. Running into the Qu’Appelle in Saskatchewan are Kaposvar Creek 5 and Cutarm Creek 6. Also trending west/east in Saskatchewan is Pipestone Creek 7. The Assiniboine spillway runs through the centre and east of the image. Prominent segments occur in the north where the Shell River enters 8, further south near Miniota 9, east of Virden 10, and near the junction with the Little Saskatchewan River 11. Entering the Assiniboine from the north are Silver Creek 12, Birdtail Creek 13, and the Little Saskatchewan River 14. The valley of the last named is prominent in its upper 15 and lower 16 reaches but almost disappears in the centre 17 although it is just as deep as to north and south. In the southeast is the Souris spillway 18—not prominent because of the sun angle—but the very small Dand spillway 19 is surprisingly obvious.
Landsat I Image: December 19, 1973
This image was made by recording Band 7—0.7 to 0.8 mm—(infrared)
Scale: 1:1,000,000 (approx.)