Ice wedge reactivated by recent aggradation of windblown sand

This is a photo of an ice wedge that underlies a surface crack on the delta (image 0210) described in the explanation of image 0064. The top of the main body of the ice body is flat, reflecting the average depth of the permafrost table in this fine sand and silt, about 1.5 m, during most of the existence of the ice wedge. The top of the small ice vein protruding upward from that flat surface represents the present depth of the permafrost table, which has been rising to conform to the rise in the surface caused by accumulation of windblown sand on top of the section. The aggradation was caused when the nearby lake’s level dropped by a few meters in the recent past, causing renewed downcutting by the stream and reactivated slumping processes that exposed the sandy deltaic sediments to renewed wind erosion. Apparently, once formed, ice wedges can grow in multiple stages at the same location in response to artificial (anthropogenic) or natural aggradation or degradation with attendant upward or downward adjustment of the frost table.

Updated 04/05/2010 AW