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.
3.4: Structural Features on the Precambrian Shield Southwest of Shamattawa
The photograph shows part of the poorly drained Precambrian Shield in northeastern Manitoba. In this area the bedrock is mapped as “felsic granulites and associated granitoid complexes with minor gabbro and anorthosite”[i] but organic surficial materials cover most of it. North Opuskiamishes Lake 1 at 137+ metres above sea level[ii] drains via North Opuskiamishes River 2 to Gods River (off the photograph). The course of the former river is structurally determined with a right-angled bend at 3. Other obvious structural lines can be seen at 4, 5, 6 and 7 with less clear examples at 8 and 9 and a complex of joints at 10. The pattern at 11 surrounding a small lake results from strings of vegetation separated by pools of water. The variable tones of the lakes on this photo result from variations in the lake surface/sun angle/camera lens relationship. However, the light tone at 12 in North Opuskiamishes Lake is caused by sediment washed in by a river.
This is the first photograph in a series (contract 711) and the specifications for the job are given in the top left-hand corner 13. The photographs were obtained from a height of 30,000 feet above sea level using a camera with a focal length of 6 inches with a Wratten no. 12 filter. Flight lines were from north to south (photo numbers 1 to 36), south to north (photo numbers 37 to 66), etc. Using the information provided it is possible to calculate the scale of the photograph using the equation f/h=i/o where f=focal length of the camera; h=height of the camera above ground level; i=image distance, that is, the distance between two objects on the photograph; and o=object distance, the distance between the same two objects on the ground. In effect i/o is the scale of the photograph. When doing the calculation, f and h must be expressed in the same units. So in this case
f=6 inches or 0.5 feet
h=30,000-449 (the height above sea level of North Opuskiamishes Lake on the 1:250,000 topographic map, 53 N Gods River).
So the scale is 0.5/29,551 or 1/59,102
The scale is 1:59,000 approximately—allowing for height variations within the area covered by the photograph.
Figure 3.4: Structural Features on the Precambrian Shield Southwest of Shamattawa
Vertical air photograph: A14215-1
Flight height: 30,000 feet a.s.l.; lens focal length 6 inches
Date: July 7, 1954
Scale: 1:39,000 (approx.)
Location: Township 76, Ranges 9 and 10 EI
Map sheet: 1:250,000 53N Gods River
1:50,000 53N/10 East Niska Lake
[i] Geological Survey of Canada. Geological Highway Map of Manitoba 1994. Winnipeg: Geological Survey of Canada, Manitoba Minerals Division, 1994.
[ii] From NTS 1:250,000 map, 53N Gods River, 1987.