Table of Contents
2: Location, Borders, and Lakes
3: Geologic Structure and Landforms
6: Pre-historic and Early Historic Settlements
7: Survey Systems
8: Southern Hamlets, Villages, and Towns
9: Mennonite and Hutterite Settlements
10: First Nations Settlements
11: Northern Settlements
12: The Southern Cities
13: Mining and Oil Extraction
15: Industry / Manufacturing
16: Water Resources
17: Parks, Recreation, Sports
18: Transport and Communications: Past and Present
19: Legal Issues and Law Enforcement
3: Geologic Structure and Landforms
Click for chapter introduction
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.
3.61: The Robertson Esker in Northwestern Manitoba
This image is different from those in figures 3.59, 3.60, and 3.61 in that it is an oblique photograph—technically a high oblique because the horizon 1 is shown. As the name suggests the camera was pointed obliquely rather that straight down as was the case in most photographs shown so far. In some ways an oblique is a more realistic view, more like the view a person gets when looking from a plane window. However, from an interpreter’s point of view obliques have problems. The scale is large in the foreground (in this case about 1:37,500) but decreases progressively away from the camera. This makes it difficult to calculate ground distances and areas.
The photograph was taken looking just south of east and shows another of Manitoba’s named eskers—the Robertson Esker 2, running northeast/southwest across the foreground. It is a very long esker traversing almost the whole of the 1:250,000 map sheet 64K, Whiskey Jack Lake, and extending into the sheet to the south 64F, Brochet. It is recognizable as a discontinuous northeast/southwest ridge running across 80 miles (129 km) of the northern Manitoba landscape. In some places it has a single ridge form 3 as where it forms the southeast shore of Ducharme Lake 4, but both to east 5 and west 6 of that it bifurcates. Eskers are composed of sands and gravels and are characteristically light-toned where they are not covered by vegetation 7. A much smaller esker 8 can be seen on the right of the photo.
This lake-strewn area falls in the open lichen woodland vegetation zone in which “the better drained upland ground cover is dominated by fructose lichens…between…scattered spruce.”[i] This arrangement can be seen in the left foreground 9, but in the background the scale is too small to distinguish details.
Figure 3.61: The Robertson Esker in Northwestern Manitoba
Oblique air photo: T104 R-55
Flight height: 20,000 feet a.s.l.; lens focal length: 6 inches
Date: September 11, 1946
Scale: 1:37,500 (approx.) in the foreground, decreasing towards the rear
Location of centre point: 58° 11'N, 100° 43'W
Map sheets: 1:250,000 64K Whiskey Jack Lake
1:50,000 64K/2 Ducharme Lake
[i] Scott, op. cit., 1996, 51-52.