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Manitoba from the Air
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Description
String Fens and Peat Plateaus East of Kettle Rapids

This is a good example “of string, net, and anastomosing fens as well as pancake-shaped, wooded peat plateaus with collapse scars. The area is situated in the northern part of the discontinuous (permafrost) zone where the mean annual temperature is -5°C and widespread permafrost is 25 metres thick. Permafrost is absent beneath both the flarks and strings at this location. The two dominant tones are related to the native vegetation: the dark tones are dominantly black spruce [Picea marina] and acid-tolerant shrubs, and the light tones are mainly tamarack [Larix laricina] and sedge with some sphagnum. Most of the peat plateaus have central depressions due to thawing of the permafrost and consequent settling of the ground. The sedge meadows in these collapse scars produce light tones. Peat thickness is predominantly 2 to 6 m. Stratified clayey silt and silty sand of glaciomarine origin underlie peat and overlie varved glaciolacustrine clay, which in turn rests on silty ablation till. Ground water running through these highly calcareous mineral sediments feeds nutrients to the fens.[i]

Fen ridges that are oriented parallel to the topographic contours are best observed along a line (1 to 2 to 3). Here the individual strings are mostly serpentine and sub-parallel, but at a few places they appear either closely interwoven or merged. They are spread apart at 4, and at 5 they are bunched together. This alternation of open and closed patterns suggests slight differences in gradient. On flatter areas the strings tend to form netlike patterns, whereas on gentle to moderate slopes they produce string patterns of variable spacing. Similar pattern variations are noticeable further west 6. Light-toned collapsed peat plateaus can be seen at several locations 7.

Notes

[i] Mollard and Janes op. cit, 1984,133.

Figure 5.28

String Fens and Peat Plateaus East of Kettle Rapids