The Geologic Origin of Mima Mounds: A New Hypothesis

Naturalist John Muir (By Francis M. Fritz [Public domain], via Wikimedia Commons)
Mima mounds, geologic structures found at the southern termini of ancient continental glaciers in North America, represent the erosional remnants of frost polygons in ancient permafrost zones. As the Earth’s climate warmed and glacial ice sheets retreated at the start of the current interglacial period, the Holocene, the disappearance of the permafrost ice wedges defining the boundaries of frost polygons produced the drainage and subsequent erosional patterns that resulted in the geologic phenomena that are now termed “mima mounds.” That these structures in North America are specifically associated with the Puget Sound and Great Lakes basins, regions understood to have been areas of continental glacial maxima during the last glacial event, is major corroborative evidence of this hypothesis.

© 2013 by Paul Kennedy