KEEWATIN POTHOLES & GLACIAL STRIATIONS

GPS Co-ordinates: N5512671, E387579 located 1 block south of Highway 17 at 6th St. in Keewatin, Ontario

These round, cylindrical holes in the outcrop appear to be man-made but they were formed by the action of running water during glaciation. Though the sign says they are "rockholes", the proper geological term is potholes. These holes are thought to have formed from water-spun rock fragments that have slowly eroded holes in the bedrock. Potholes occur throughout the Kenora-Keewatin area and may be as large as 2 or 3 m deep and 2 m in diameter.

A small outcrop at the entrance to the boardwalk displays glacial striations. The rocks in this outcrop have been polished and scratched by the movement of a glacier. The long grooves and scratches on the outcrop surface are glacial striations. These were formed by fragments of rock, embedded in the ice at the base of the glacier, which scratched and gouged the outcrop surface as the ice moved over the land.

About 18000 years ago, an extensive sheet of thick continental glacial ice, referred to as the Laurentide Ice Sheet, covered 90 percent of Canada including Lake of the Woods.  The erosive action of glacial ice and meltwater carved and sculpted the bedrock surface of the land and deposited surface materials such as sand and gravel.  The Keewatin rockholes are an example of water sculpted erosional forms left behind by the glacier.

The rockholes are round rimmed shafts, deeper than they are wide with internal spiral grooves.  The rockholes were sculpted into the hard bedrock surface by the action of swift jet-like streams of swirling glacial meltwater that carried a considerable amount of gravel and fine sedement.  The high velocity, sediment-laden water eroded circular depressions into the rock by abrasion and grinding.  The four holes in the rock range in diameter from 30 inches to several feet with a depth range from four to seven feet.

The Keewatin rockholes provide evidence for glaciation in the Lake of the Woods area and demonstrate that sediment-laden, high-velocity water can perform major and unusual feats of erosion.