Which Way to the (Ancient) Beach? The Shoreline of Glacial Lake Iroquois

1914

Lake Iroquois

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Looking south from the elevation of Hillcrest Park, it's easy to see the 2 km dip into the lake; not Lake Ontario, however, but a large, ancient reservoir.

1914 Bathurst Street looking north to Davenport Rd., 1914, Courtesy City of Toronto Archives, Fonds 1231, Item 237.

The parts of Toronto south of Davenport Road were once submerged in a large glacial lake known as Lake Iroquois. That ancient lake’s water levels were roughly 30 m above those of present Lake Ontario. The former east-west shoreline of Lake Iroquois, which shrank dramatically 12,000 years ago, left behind a 15 m high bluff just above Davenport Road — the ridge that Casa Loma sits on.

In essence, Lake Iroquois was a larger version of Lake Ontario, with a winding shoreline that followed the similarly meandering Davenport Road. For approximately 80,000 years, the Laurentian Ice Sheet covered much of Ontario and when the ice sheet began to retreat 12,500 years ago, the melting water filled up the basin, becoming Lake Iroquois. This ancient lake drained via the Mohawk Valley near Rome, New York, as it couldn't use its current outlet, the St. Lawrence River, which was still blocked by ice. Once the ice melted and the St. Lawrence opened up, Lake Iroquois drained through it, and water levels plummeted, leaving the imposing bluff on which Hillcrest Park stands.

By Claire van Nierop

1914 Bathurst Street looking north to Davenport Rd., 1914, Courtesy City of Toronto Archives, Fonds 1231, Item 237. View the image gallery