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
3.17: Rain Splash Erosion on Ground Moraine Near Minnedosa
The area is underlain by hummocky ground moraine on which there is no integrated drainage pattern. Many hollows are occupied by sloughs (small lakes) 1, although some of them have been infilled or drained 2. In some places the farmer has constructed drainage ditches to improve surface drainage and help in slough removal 3. Most of the area has been cleared for agriculture, but rings of vegetation—sedges, bulrushes, cattails, and dwarf willows—surround the sloughs4.[i] In this late summer photo some of the land is cropped 5, but some areas have been left fallow 6. On the fallow land rain splash has removed fine-grained and dark-coloured organic constituents of the soil from ridges, leaving behind light-toned coarse materials. The result is that even minor ridges of a few metres height stand out as light-toned areas 7. This effect is partially masked where the land is cropped but can still be observed 8.
The area displays the grid of the DLS system. Gravel roads follow section lines which can be easily seen 9, but quarter section lines are reflected by differences of land use and are not so easily identified 10. Six farms 11 exist in the area with most farm buildings being protected from the prevailing northwest winds by trees planted for this purpose 12. On this early morning image shadows are thrown almost due west 13.
Figure 3.17: Rain Splash Erosion on Ground Moraine Near Minnedosa
Vertical air photograph: A18971-2
Flight height: 8,720 feet a.s.l.; lens focal length: 152.32 mm
Date: October 22, 1964
Scale: 1:17,000 (approx.)
Location: Township , Range
Map sheets: 1:250,000 62J Neepawa