Strudel and rib-and-trough features in a tundra lake 2
This photo shows the juxtaposition of strudel and rib-and-trough features in a lake west of Hudson Bay, in southwestern Nunavut, Canada. The date of the photo is unknown but it was probably taken in the late 1970s. These crater-like features, described by the author and Walter Dean (Shilts and Dean, 1975) and by Reimnitz, Rodeick, and Wolf (1974), are formed by jets of water forced through holes in lake ice as it rises abruptly in the spring, when the force of its buoyancy exceeds the strength of the freezing bond to the bottom. Where the bottom is soft, as in this example, the vortices resulting from water jetting through holes in the ice excavate sediment, which settles immediately around the resulting depression, forming a natural levee-like rim (see images 0203 and 0124 for close-up views). Where probed by divers, frozen sediment marking the permafrost table was found to underlie the bottoms of the holes at depths of 30-40 cm, which probably limits the depths to which the holes can be excavated. See also images 0047, 0071, 0119, 0123, 0126, 0204, and 0206.
Updated 04/08/2010 AW