| Summary: | Field observations in the Mackenzie Delta area largely substantiate Lachenbruch's theoretical considerations of thermal contraction crack development. Frost crack patterns, representing the incipient stage of tundra polygons, were observed on both bare and vegetated surfaces of low alluvial flats and sandspits of three islands. Individual polygons, where developed, ranged in size from 20 to 30 metres diameter on bare surfaces to 2 to 3 metres on sedge-covered areas, and 80% of the angular intersections measured were of orthogonal type. Most cracks exhibited random orientations, except in close proximity to water bodies where tendencies toward normal and subparallel orientations occurred.
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