A Vast Lake Trapped Under Ice Sheet Drained Into The Sea, Bringing Down Temperatures Paris: Canadian geologists say they can shed light on how a vast lake, trapped under the ice sheet that once smothered much of North America, drained into the sea, an event that cooled Earth's climate for hundreds of years. During the last ice age, the Laurentide Ice Sheet once covered most of Canada and parts of the northern United States with a frozen crust that in some places was three kilometres thick. As the temperature gradually rose some 10,000 years ago, the ice receded, gouging out the hollows that would be called the Great Lakes. Beneath the ice's thinning surface, an extraordinary mass of water built up
