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Table of Contents
Foreword
Preface
Glossary

Chapter 3: Geologic Structure and Landforms

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

Figure 3.96: The Bald Head Hills South of Carberry

Figure 3.96

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

Notes

[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.