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 photo is of an area just north of that in figure 3.71. Here the strandlines at the base of Duck Mountain (off the photo to the west) trend north/south. PTH 10 1 follows the Campbell Beach. Just to the east is another strandline followed by secondary roads 2, and further east still are a series of indefinite strandlines 3 that are both lower and newer. They can be identified on the basis of land use variations 4 and tonal variations in fields 5. In the northwest quadrant are higher, older strandlines, one of which coincides exactly with cleared woodland 6, whereas others are indicated by tonal variations in fields 7. Strandlines are often good sources of sand and gravel for road construction and other uses; two gravel pits 8 can be seen west of the Campbell Beach. Drainage is generally from west to east off Duck Mountain but in one case, Drifting River 9, its direction is profoundly influenced by strandlines. Also Broken Pipe Lake 10, which receives streams from the west 11, is backed up behind the Campbell Beach and has no obvious outlet.
The checkerboard pattern of the DLS system is clear, but there is an interesting variation in this area. Three different systems of survey were developed for use in western Canada, of these the first and third were employed in western Manitoba.[i] The first system was used south of Duck Mountain and the third covers northern areas, the boundary between the two being at the seventh correction line (i.e., the northern edge of township 26). So township 27 is the first township in the third system; it is distinctive in that it is only four sections deep—all of which are on the photo—compared with the normal six. The differences between the first and third systems are relatively minor: 1) road allowances are 66 feet in the third system compared with 99 feet in the first; 2) east/west road allowances occur along the northern edge of each section in the first system, but occur only every other section in the third system. The first difference is not visible on the photo but careful inspection shows east/west gravel roads a mile apart in some areas in township 26 12 but two miles apart in some areas in township 27 13. A small correction occurs between townships 26 and 27 resulting in a jog in PR 274 14. PR 267, an east/west road 15, follows the divide between townships 27 and 28. Finally a light-toned line in the northeast indicates the route of a power line 16.
Figure 3.72: Lake Agassiz Strandlines East of Duck Mountain
Vertical air photo: A21750-34
Flight height: 25,200 feet a.s.l.; lens focal length: 88.89 mm
Date: July 27, 1970
Scale: 1:83,400 (approx.)
Location: Township 26, 27 and 28; Ranges 21 and 22 WI
Map sheets: 1:250,000 62N Duck Mountain
1:50,000 62N/1 Dauphin
62 N/8 Sifton
[i] Tyman, J. L. By Section Township and Range (Second Printing). Brandon: Brandon University, 1995, 13.