The Great Lakes are kettle lakes; they were left over from the Pleistocene glaciers. As the glaciers were retreating, the Great Lakes underwent a change. Once the weight of the glacier ice decreased, and the pressure decreased, the land at the bottom of the lakes rose. In some places it rose by as much as one hundred feet. [Kettle lakes get their name from their resemblance to a kettle or pot-shaped depression in the ground.] #toefl_vocabulary