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.
3.19: Soil Erosion on End Moraine Near Bruxelles
This area lies within the end moraine-covered Pembina Hills. The small Cypress River 1 flows from east to west in a mainly wooded valley 2. Most of the area has been cleared for agriculture although a few clumps of deciduous woodland have been left 3.
The agricultural land has been subjected to rain splash erosion producing the typical mottled appearance of bald crests and darker hollows 4. Numerous gullies radiate from an elevated area in the south 5, and severe soil erosion is evident at other locations 6.
The area is divided according to the squared DLS system, although the sections are not completely regular in shape perhaps due to errors in the original survey. Roads follow section lines 7, and some quarter sections can be identified on the basis of land use variations 8. PTH 34 9 traverses the area from north to south. The CypressRiver has been straightened to improve drainage at the road crossing 10.
Ten farms are located in this area of about six square miles. Several of them show the standard arrangement of farm buildings surrounded by trees planted for shelter 11. Very dark fields have been left fallow 12. Crops at various stages of development cover lighter-toned fields 13. Cereal crops near harvesting stage probably cover very light-toned fields 14.
Figure 3.19: Soil Erosion on End Moraine Near Bruxelles
Vertical air photograph: A16185-153
Flight height: 10,500 feet a.s.l.; lens focal length: 152.63 mm