Chapter 3: Geologic Structure and Landforms
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
3.89: Tobacco Creek Near the Western Edge of the Red River Plain
The photo shows Tobacco Creek 1 wandering eastwards across the Red River Plain. Although the creek has been straightened both west and east of the photo, it follows a natural channel here. Deciduous woodland—dark toned—grows along its course. Other channels, not wooded and only occupied in wet conditions, can be seen in two other locations 2.
Although the relief here is minimal, it is enough for rain splash and wind erosion to remove dark-coloured soil constituents from higher areas, leaving light-toned zones 3. Two minor strandlines can be seen in the east 4. Two farms are located on the most prominent strandline.
Apart from the Tobacco Creek course, virtually all the land is intensively farmed with many fields in one quarter section 5. Two farms are located close to Tobacco Creek 6—probably for water supply—and others can be seen close to section lines 7; most of these have planted shelterbelts 8. Four also have dugouts 9. Gravel roads follow section lines with a minor bend to avoid Tobacco Creek 10. The CP lines run north/south across the area at a slight angle to the DLS system 11.
Figure 3.89: Tobacco Creek Near the Western Edge of the Red River Plain
Vertical air photograph: A16183-14
Flight height: 10,500 feet a.s.l.; lens focal length 152.63 mm
Date: July 22, 1958
Scale: 1:18,900 (approx.)
Location: Township 5; Range 4 WI
Map sheets: 1:250,000 62 H
1:50,000 62H/5 Roland