Contrast between a mudboil-covered till surface and degrading frost polygons
image is a closer view of the background of the left side of image 0072,
which has an explanation of the scene. Note the large number of active mudboils,
which in this region indicate the presence of red clayey till (see image
0091) or marine, fine-grained, offshore sediments.
Fine-grained marine sediments (from the post-glacial Tyrrell Sea) undoubtedly
underlie, at depth, the lower areas characterized by frost
cracks, but the organic peat that develops in these poorly drained sites
thaws to less than 50 cm, causing the rigid, perennially frozen, underlying
sediments to retain their cracks, which enlarge seasonally. The frost cracks
in this image are “degrading” during this particularly hot summer,
and the water from the melting ice wedges
is pooled over the cracks. Note, also, the strongly developed solifluction
stripes that are best developed on areas of active mudboils in this region.
The dark part of the stripes is characterized by low, brushy vegetation
(dwarf willow, dwarf birch, Dryas integrefolia, etc.) that
grows preferentially on the wet depressions between lobes. See detailed
discussion for image 0240.
Photo by Dr. A. N. Boydell
Updated 05/06/2010 AW