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 photograph covers an area just north of that shown in figure 3.73. The main part of The Pas moraine is located to the northeast 1. A series of Lake Agassiz strandlines appear as minor elevations 2 with slightly different vegetation than their surrounds. The waters of the lake that was in the southwest shaped a hooked spit 3 in the centre of the photo. Extending southward from the lakeward end of the spit 4 is an area of string bog 5 in which water is dark grey 6 and strings of vegetation running across the gentle slope appear in lighter tones 7. A roughly circular lake 8—partly unfilled—is located southeast of the string bog. PTH 10 9, light-toned, cuts across the northeast corner; two dark-toned vehicles 10 can be seen on the road. A cut line 11 leads south-southwest from the road; it is light-toned where it cuts across the strandlines and the spit 12 but dark-toned where it cuts across the less well-drained marshy land to the south 13. A trail 14 leads west along the spit. This area lies within the mixed woods (coniferous/deciduous) vegetation zone[i]. Coniferous trees can be identified on the basis of their triangular shadow shape best seen in a clearing in the northwest 15.
Figure 3.74: Lake Strandlines and Spit on The Pas Moraine, South of Westray
Vertical air photograph: MB95001-211
Flight height: 6,800-7,800 feet a.s.l.; lens focal length: 152.815 mm
Scale: 1:12,000 (approx.)
Date: May 13, 1995
Location: Township 51; Range 27WI
Map sheets: 1:250,000 63F The Pas
1:50,000 63F/6 Not title
[i] Scott, op. cit., 1996, figure 4.2, 45.