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.
3.41: River Capture on the Souris River South of Wawanesa
In immediate post-glacial time, a river flowed along the southern edge of the Tiger Hills (part of the Darlingford end moraine) occupying a spillway that now contains the Souris River, Langs Valley, Pelican Lake and Lorne Lake. The spillway used to carry water from glacial lakes, Souris and Hind, in the west to glacial Lake Agassiz in the east. At that time the proto-Souris, a tributary to the Assiniboine, was extending itself southwestward by headward erosion into, and eventually through, the Tiger Hills, possibly occupying an old glacial melt water channel through the hills. Eventually the proto-Souris met up with and captured the flow of the river in the spillway.
Today the Souris 1 takes a sharp bend at the elbow 2 and then flows through the Tiger Hills 3 in a steep-sided gorge. A small, unnamed stream 4 flows westward against the original flow to join the Souris at the elbow. Above the elbow, the Souris has incised a steep-sided inner valley into the floor of the spillway, the sides of which can be seen to the north 5 and south 6. On the north side a terrace 7 represents a former water level in the spillway. The south side is broken by two small gullies 8.
Since capture, the Souris has eroded rapidly through the end moraine of the Tiger Hills into the underlying shale that can be seen at a sharp bend in the river 9. Slumping has occurred on the west side of the valley 10. The river’s speed of the flow is fast for a prairie river and shallow rapids can be seen on this summer image 11. The south bank (north-facing) is heavily wooded but the north side—south facing and therefore drier—is covered by a mixture of grasses and trees, the latter in evidence in wetter “draws” 12. Both sides of the gorge through the Tiger Hills are thickly wooded, but the hills themselves have patchy woodland surrounded by grass.
A gravel road, PR 346 13, runs north/south across the area with a rare—for southern Manitoba—hairpin bend 14 on the south side of the spillway.
Figure 3.41: River Capture on the Souris River South of Wawanesa
Vertical air photograph: A11048-244
Flight height: 9,520 feet a.s.l.; lens focal length: 6 inches
Date: May 31, 1947
Scale: 1:15,840 (approx.)
Location: Township 6; Range 18 WI
Map sheets: 1:250,000 62 G Brandon
1:50,000 62G/5 Dunrea