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.
3.25: The Assiniboine Glacial Spillway: Meanders and Abandoned River Segments
Here the Assiniboine spillway floor varies from under one mile (1.5 km) to over two miles (3.2 km) in width. The main river channel hugs first the southwest bank of the spillway 1, then the northeast 2, before transferring back the west bank 3. Two small abandoned meanders can be seen 4, but more obvious are long segments of the river that have been left behind by the migrating river 5.
The Assiniboine wanders across the spillway floor in a series of irregular meanders, leaving behind clearly defined meander scrolls 6. Part of the floodplain in the northwest has been reclaimed for agriculture and is protected from flooding by the main river channel by an embankment (dike) 7. Even so some of the land, the site of the old river channel, is too wet for agriculture 8.
The south and west bank of the spillway is steep, well-wooded and broken by only one minor gully in the south 9, whereas the north and east bank is less steep, not so uniformly wooded because of the dry microclimate on southwest and west facing slopes, as well as being broken by four major gullies 10 and many minor ones.
Flat land exists on either side of the spillway. In the west glaciofluvial materials pulled into northwest/southeast trending ridges underlie the surface 11. Linear sloughs occupy depressions 12, and the surface is covered by scrubland with patches of trees 13. East of the spillway much of the land is used for agriculture. Light-toned hillcrests can be seen in fallow fields 14. Roads follow the section lines of the DLS on flat land but are influenced by the topography on the spillway sides 15.
Figure 3.25: The Assiniboine Glacial Spillway: Meanders and Abandoned River Segments
Vertical air photograph: A15527-134
Flight height: 20,000 feet a.s.l.; lens focal length: 152.26 mm
Date: October 7, 1956
Scale: 1:37,300 (approx.)
Location: Township 12 and 13, Ranges 25 and 26 WI
Map sheets: 1:250,000 62K Riding Mountain
1:50,000 62K/2 Hamiota