Relict Thermal-contraction-crack Polygons and Past Permafrost South of the Late Wisconsinan Glacial Limit in the Mid-Atlantic Coastal Plain, USA

The paucity of reports on relict thermal contraction crack polygons in the mid-Atlantic Coastal Plain and many other areas in eastern North America has hampered our understanding of the extent and nature of past permafrost south of the Late Wisconsinan glacial limit. Examination of Google Earth imagery revealed orthogonal to hexagonal polygons, mostly 10-30 m in diameter, at more than 160 sites in sand and gravel deposits in southern New Jersey and the Delmarva Peninsula. The polygons are interpreted to indicate that continuous permafrost extended to 38.5 degrees N in a zone more than 250 km wide to the south of the glacial limit under a mean annual air temperature of -6 degrees C probably during the Late Wisconsinan. Copyright (c) 2014 John Wiley & Sons, Ltd.