MB GeoTour 27 – Spruce Woods Provincial Park, Spirit Sands 2012

The Spirit Sands are located in the Bald Head Hills, within Spruce Woods Provincial Park east of PTH 5 (13-8-14W1, NTS 62G11NW, NAD 83, Zone 14U, 479095E, 5501281N).

Summary

The Spirit Sands of Spruce Woods Provincial Park are a rare, but excellent example of wind-blown geological phenomena that is presently occurring on the upper surface of the Agassiz delta in south-central Manitoba. The ancient delta was deposited by the ancestral Assiniboine River in glacial Lake Agassiz at the end of the last ice age. The desert-like sand dunes are slowly being stabilized by plants thanks to sufficient precipitation and groundwater combined with relatively mild temperatures. More information on the Spirit Sands can be found at: https://www.gov.mb.ca/conservation/pa....

This video shows the Bald Head Hills, or Carberry Sandhills, that are found along the Spirit Sands self-guiding trail within Spruce Woods Provincial Park in south-central Manitoba. An informative interpretative centre at the trail head, describing the features of the Spirit Sands; and numerous plaques describing aspects along the trail have been constructed by Parks Branch of Manitoba Conservation. A detailed map for Spruce Woods Provincial Park can be found at: https://www.gov.mb.ca/conservation/pa....

The Recent hills developed as large windblown, or aeolian, dunes on an ancient delta that formed in glacial Lake Agassiz at the end of the Pleistocene (or end of the last ice age). The 6500 km2 Agassiz delta formed at the mouth of the former glacial Assiniboine River from sediment carried by the river as the continental ice sheet melted from North America. The sediment was derived from numerous tributaries that fed the glacial Assiniboine River, from as far west as the Rocky Mountains and as far north as Nunavut and Northwest Territories. The sediment that dropped out to form the delta in glacial Lake Agassiz was mainly fine to coarse sand and silt. Coarser rock particles, such as boulders and cobbles, were mainly deposited much further upstream, nearer to the Manitoba-Saskatchewan boundary, and even still farther to the west and north.

As the ice receded from North America, newly exposed outlets from glacial Lake Agassiz allowed drainage from the lake to change from southward into the Mississippi River, to eastward into Lake Superior, and finally northward into the Hayes and Nelson rivers. Accompanying this change in flow direction was a reduction of water levels in the lake, marked by a series of steps forming a succession of beach ridges that developed on the upper surface of the delta. Gradually, the delta became high and dry enough to allow the prevailing winds to move the sand and silt into large migrating sand dunes that form the Spirit Sands.

Over the past 200 years the climate has moderated from the previous Little Ice Age, with increasing moisture (averaging 300-400 mm) and relatively mild temperatures. This has allowed vegetation (aspen, oak and white spruce (the arboreal emblem of Manitoba) to gradually become more and more established, stabilizing much of the delta surface from wind-blown erosion. Now, only small portions of the original unstabilized (desert-like) surface of the delta remain, which can be seen in the Bald Head Hills, and at a few other localities.

The result of the relatively continuous movement of sand and silt particles can be seen in the video, where the trunks of fully developed trees have been buried by the migrating dunes. Also shown, is an example of the relentless wind that can catch the unwary by surprise, demonstrating that the “Spirits are at always at work”, when you least expect them.

Reference:
Huck, B. and Whiteway, D. 2015: In search of Canada’s Heartland; Heartland Associates Ltd.,
Winnipeg, 320 p.