The last 2 million years has seen Canada and the Northern USA locked in an Ice Age with glaciers continually advancing and retreating over the landscape. The Wisconsinan glaciation was the last major ice advance which covered most of Canada and parts of northern US. In some parts of Ontario, the ice was over 2 km thick!
13,000 years ago, as the glaciers began to retreat, and melting progressed, the ice over Southern Ontario divided into 2 lobes, forming a distinct crack that ran along the future ridgeline of the Oak Ridges Moraine. Torrential flood channels developed beneath the melting ice, carrying sediments and dumping them into the crack. These formed the initial core of the Moraine.
9,000 years ago, after the ice sheets and giant glacial lakes seeped away from Southern Ontario, the Oak Ridges Moraine remained: up to 200 metres thick and rising to over 300 metres above Lake Ontario.
You can watch 12,000 years of geological history in our Moraine Formation learning object! Note that this object requires the Macromedia Flash player and may run slowly on a dial-up connection.