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 large-scale air photo shows detail of the Swan River Delta. Swan River 1 flows northeast into Swan Lake 2 and along with its distributary, Rat Creek 3, has deposited a bird’s foot type of delta. Wooded levees 4 follow the course of Swan River. Back from the levees are marshy areas 5 and lakes 6 with some higher, wooded areas 7. Sediment swirls are clearly seen in the lake 8.
Vertical air photograph: A15607-105
Flight height: 19,800 feet a.s.l.; lens focal length: 152.14 mm
Scale: 1:38,500 (approx.)
Date: June 1, 1957
Location: Township 40; Ranges 23 and 24W1
Map sheets: 1:250,000 63C Swan Lake
1:50,000 63C/7 Lenswood