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A Journey to a New Land

Multimedia Library

Dr. John Clague

Department of Earth Sciences, Simon Fraser University


These are sort of sinuous ridges, sort of snake-like ridges of gravel and if you live on the Canadian Shield or in the Prairies you have probably come across these ridges that extend for sometimes tens of kilometers across the landscape. They are in-fillings of tunnels that develop beneath an ice sheet. As an ice sheet melts, there are channels that develop in the base of the ice, so you get a tunnel that carries water, sort of a conduit for water that is flowing off the ice sheet, but at the base of the ice sheet. And those streams at the base of the ice are carrying a lot of sand and gravel and the sand gets deposited in these conduits and essentially plugs them up. When the ice finally disappears, you no longer have the physical evidence of the ice, but you have an inverted channel that forms this ridge.