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.
3.43: Spring Sapping Along the Banks of the Assiniboine River in Canadian Forces Base (CFB) Shilo
In this area, below Brandon, the Assiniboine River 1 has incised itself into the sands and clays of the Assiniboine Delta. The light tone of the river, caused by reflection from suspended sediment, contrasts with the dark tone of a cutoff with no suspended sediment 2. Spring sapping, where ground water comes to the surface at the junction of permeable sands above with impermeable clay below, has resulted in the retreat of the river’s north bank producing a scalloped edge 3 with occasional deeper embayments 4. On the river’s south side, scroll bars 5—some emphasized by trees 6—can be seen. Trees in the river valley are mainly deciduous with occasional patches of coniferous trees—mainly white spruce (Picea glauca)—identified by their dark tone 7 and conical shadow shape 8.
North of the river is a light-toned, grass-covered plain 9 with scattered dark-toned patches 10; these are clumps of creeping juniper (Juniperus horizontalis), a species that grows well on the thin sandy soil. Further north are stabilized sand dunes 11 with some poorly defined longitudinal dunes 12 that support dark-toned coniferous trees, mainly white spruce (Picea glauca). Other areas are covered by light-toned grasses 13 and medium-toned woodland 14, mainly trembling aspen (Populus tremuloides).[i]
Within the river bend land is used for agriculture, and a large gravel pit exists 15 that exploits gravel and sand left behind in scroll bars as the river migrated northwards. Land north of the river is part of Canadian Forces Base (CFB) Shilo and is used for military training. Two sand/gravel roads exist 16 as well as many light-toned paths 17 used to transport vehicles during military exercises.
Figure 3.43: Spring Sapping Along the Banks of the Assiniboine River in Canadian Forces Base (CFB) Shilo
Vertical air photo: A23692-29
Flight height: 13,700 feet a.s.l.; lens focal length: 153.22 mm
Date: May 12, 1974
Scale: 1:25,000 (approx.)
Location: Townships 7 and 8; Range 15 WI
Map sheets: 1:250,000 62G Brandon
1:50,000 62G/11 Glenboro
[i] For details see Kerr, Rounds, and Welsted, op. cit. 1978, 408-414.