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.
3.96: The Bald Head Hills South of Carberry
The main requirement for sand dunes to form is a plentiful supply of sand which can be transported and subsequently deposited by the wind. In southern Manitoba
this requirement is met principally where sediments were deposited into glacial lakes, particularly lakes Agassiz
and Hind, which retreated or dried out leaving deposits open to wind action. Dunes are also found on some glacial outwash deposits and along the shores of some major lakes.
The largest area of dunes in Manitoba is located on sands which are part of the Assiniboine Delta deposited into the west side of Lake Agassiz: “The main area of contiguous uninterrupted dunes (both stabilized and active) is estimated at 960 km2.” It is fourth largest such region in Canada.[i] Sand deposits are up to 70 metres thick. “As the lake drained, the sediments were exposed and reworked by wind into landforms ranging from low mounds and hills to true dunes. The most common type is the parabolic dune, often quite elongated. These may be grouped into large complexes, appearing as a series of “waves” or “chains.”[ii]
The photograph shows a group of active dunes known as the Bald Head Hills. Bare sand is almost white on the photograph. The dune waves have a gentle upwind side (to the northwest) and a steep lee face (to the southeast). Tracing the dunes from the southeast, at least seven faces 1 can be seen with steep slopes at the angle of repose of the component sands (about 35°). On the gentle windward slopes, ripple marks can be identified especially on the first three dunes, counting from the southeast 2; and at the back of each slope, vegetation (grasses and trees) is growing in the lowland between dunes 3. The dunes are moving slowly to the southeast in response to the prevailing northwest winds, in some cases burying trees in the process.
Another dune complex can be seen further north 4. Here there is less bare sand, although some is seen near the southeastern edge 5. The area is mainly grass-covered, but all this area was active in 1928. Also recent photographs and personal observation reveal there is much less bare sand in the southern dune complex than there was at the time of the photo.[iii] In addition to the two dune complexes, there are two dune ridges 6 both of which are now stabilized by grass and trees.
This area lies in a region where three major North American vegetation formations overlap: the Grassland (or “prairie”), the Boreal (northern coniferous) Forest, and the Temperate (eastern) Deciduous Forest. On the photograph grassland can be seen in the southwest. It has a light grey tone and smooth texture 7. It surrounds patches of deciduous trees; mainly aspen (Populus tremuloides) that have almost the same tone, but a mottled texture 8. West of both dune complexes are stands of dark-toned coniferous trees mainly white spruce (Picea glauca) 9. Isolated coniferous trees, identified on the basis of their dark tone and triangular shadow shape, can be seen on the plain behind the dune complexes 10. It is noticeable that on the dune ridges, trees—mainly coniferous—cover the north facing slopes 11, whereas the south-facing slopes are bare or grass covered 12, a reflection of a drier microclimate on the south-facing slopes.
The white line in the east 13 is a path that was probably originally a fireguard but is now used for visitor access. The Bald Head Hills are now part of the Spruce Woods Provincial Park. They attract numerous visitors to the “Manitoba Desert”.[iv]
Figure 3.96: The Bald Head Hills South of Carberry
Vertical air photograph: A16405-16
Flight height: 10,500 feet a.s.l.; lens focal length: 152.63 mm
Date: October 19, 1958
Scale: 1:18,600 (approx.)
Location: Township 8; Range 14 WI
Map sheets: 1:250,000 62G Brandon
1:50,000 62G/11 Glenboro
[i] Rogosin, op. cit., 1996, 56.
[ii] Rogosin, op. cit., 1996, 56.
[iii] “Of the original 6,500 square kilometers of deltaic sand, only 4 square kilometers remain open” Guide to Spruce Woods Provincial Park. Winnipeg: Manitoba Natural Resources, 1998.
[iv] The area of open sands is also referred to as The Spirit Sands or the Manitoba Desert.