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.
3.87: The Lake Agassiz Plain South of Roland
The plain left behind once Lake Agassiz retreated from southern Manitoba is one of the most extensive flat areas in the world. This high-level, small-scale photo covering about 133 square miles (344 sq km) gives a good impression of the plain that is almost completely flat except for an inperceptible decline to the east, towards the Red River. The slope results in a series of minor eastward flowing intermittent streams from north to south: Graham Creek 1, an unnamed creek 2, North Shannon Creek 3, Shannon Creek 4, Thornhill Coulee 5, and Deadhorse Creek 6. Several creeks have been straightened to increase the speed of flow; for example, Graham Creek 7, the unnamed tributary of North Shannon Creek 8, and Shannon Creek 9.
Until the beginning of the Twentieth Century this area was marshy and useless for agriculture until an intricate system of drainage ditches was constructed. The straightened steams are at the top of a hierarchy of drainage channels; at lower levels are hundreds of kilometres of minor channels not seen on this photo either because they are too small or because they run parallel to section lines. Although there is a limited amplitude of relief, minor depressions are wetter—and therefore darker—producing a mottled effect 10. Also two minor strandlines trending north-northwest/south-southeast can be seen 11, one of which is exploited for sand 12.
Once the soils were drained, they were excellent for arable agriculture. Consequently, apart from a few wooded, deciduous areas along creeks 13, the whole area is devoted to crop growing. Usually there are one, two, or three farms per section 14, their location being determined by the DLS system. The land is used intensively often with many fields in one section 15, in contrast with one to four per section in southwestern Manitoba. Wind is a problem in the flat area; consequently, nearly all farms have shelterbelts to north and west 16, and field shelterbelts have been planted in two locations 17. Road location is determined by the DLS system although PTH 23 18 detours around Roland 19. In this settlement roads are rather surprisingly oriented with respect to the DLS system rather than the CN railway line which passes through it 20. An abandoned line 21 enters Roland from the southeast and continues north.
Figure 3.87: The Lake Agassiz Plain South of Roland
Vertical air photo: A21852-12
Flight height: 24,100 feet a.s.l.; lens focal length 85.55 mm
Date: August 12, 1970
Scale: 1:81,200 (approx.)
Location: Townships 3, 4, and 5; Ranges 4 and 5 WI
Map sheets: 1:250,000 62G Brandon
1:50,000 62G/8 Miami