Laurentian River

1899 estimate of the course of the Laurentian River.

The Laurentian River was an ancient river that flowed east in what is now the Province of Ontario and State of Michigan. It flowed, on the surface, prior to the most recent series of glaciation, of which the Laurentide glaciation is the most recent.

The glaciers buried the river valley in sand, gravel, and other glacial till. But groundwater still slowly flows through the valley.

In 2003 when engineers bored a test hole, in Toronto's High Park, they tapped into the underwater flow, and found high pressure water spurted from the test hole, like a geyser.