The Mink Lake Sill

A description with photographs of the Mink Lake Sill. This sill largely controlled the flow of glacial melt water down the Petawawa River Valley during the Wisconsin deglaciation.
The Mink Lake Sill between Mink Lake and Cauchon Lake in Algonquin Park

(photo by Diana: 2014-06-25 - map - explore

The Mink Lake Sill a little west of the portage from Cauchon Lake into Mink Lake.

O.K., now imagine the same scene with 10 metres of water flowing over that little cliff.

For several hundred years, the drainage of proglacial Lake Algonquin was over the Mink Lake sill and down the Petawawa River basin.

Over 10,000 years ago, the glaciers were retreating. As the glacier melted from what is now Algonquin Park, the ice front ran roughly east-west (but somewhat north of west and south of east) and was retreating somewhat east of north. To the west, Lake Algonquin, the forerunner of the modern upper Great Lakes had formed with water levels 50-100m higher than the present Great Lakes. At first, Lake Algonquin drained southward through the Mississippi River, but as the ice retreated a lower outlet was exposed and the drainage shifted to Lake Simcoe and the Trent River system. As the ice retreated farther north, an entrance into the Ottawa Bonnechere Graben was exposed. This provided an even lower outlet for Lake Algonquin, first down the Petawawa River system and then down the Mattawa River to the Ottawa River. Drainage down the Mattawa / Ottawa River system continued for about 5000 years until the crust rebounded from the weight of the glaciers sufficiently that the drainage switched to its modern configuration over Niagara Falls and out the St. Lawrence.

Lake Algonquin probably drained down the Petawawa River system for several hundred years although the exact chronology is uncertain. The details of the drainage varied as the retreating ice exposed more and more of the Petawawa basin.

The first drainage into the Petawawa system may have occurred in the vicinity of South River. The route would have been through Kawawawaymog Lake / Biggar Lake / Skuce Lake to the Nipissing River. However, it has been argued (Chapman and Putnam) that an esker crosses the Nipissing River south of Carl Wilson Lake and is cut through only by a narrow diagonal gap. They concluded that it is therefore doubtful that this ever served as an outlet channel as the esker would have been washed away ( 1 ). Further there does not seem to be any field evidence in support of the South River outlet.

In addition to the South River outlet, Harrison has proposed a series of openings into the Petawawa drainage system. These were:

  1. The Genesee Outlet. The controlling sill for this outlet is ill defined but there is evidence of significant flow south of the Genesee Moraine.
  2. The Fossmill Outlet. The controlling sill for this outlet is between Kilrush and Dog Lake at 1,140 ft.
  3. The Sobie-Guilmette Outlet. The controlling sill for this outlet is the eastern end of Guilmette Lake at 1,125 ft.
  4. The Mink Lake Outlet. The controlling sill is between Mink Lake and Cauchon Lake at 1,075 ft.

For all of theses outlets, the flow went over the Mink Lake sill, but it is only for the last outlet that it was controlling.

Downstream of the Mink Lake sill, the glacial melt water took different paths depending upon the position of the ice front. Ford and Geddes suggest that a series of three major drainage systems operated sequentially in the eastern part of the park to carry water discharged from Lake Algonquin to the Champlain Sea. These were:

  1. The Bonnechere River valley
  2. The Barron and Indian Rivers, fed sequentially by Carcajou Creek and then the Grand Lake system
  3. The lower Petawawa River valley

Ford and Geddes further argue (citing work by Dadswell) that the flow down the Bonnechere River was controlled by a sill south of White Partridge Lake at an elevation of about 380m (1,250 ft). Even after correcting for isostatic rebound, the elevation of this sill is higher than the Genesee and subsequent outlets. Consequently, those outlets must have still been blocked by ice or drowned when the White Partridge drainage was active. Further, there must have been an embayment of Lake Algonquin well into present day Algonquin Park. The embayment was bounded on the west by the western flank of the Ottawa Bonnechere Graben and to the north and east by the receding glacier. The White Partridge sill was the eastern limit of the embayment and would have controlled the Lake Algonquin drainage. The Fossmill and related outlets were active after the discharge shifted from down the Bonnechere River valley via the White Partridge sill to drainage down and Barron and Indian River systems via Carcajou Creek (and later Grand Lake).

As the glacier receded to the north-northeast, Clemow Lake and the northwest end of Grand Lake were uncovered. The flow switched to Grand Lake with a sill near Brawny. Flow finally switched to the lower Petawawa River once the glacier had fully cleared the Petawawa River valley beyond Lake Travers.

The sill at Mink Lake would then have been controlling once Grand Lake opened up and perhaps sooner. It would remain active until the glacial drainage switched to the Mattawa River and all Lake Algonquin drainage down the Petawawa basin stopped.

For more details and maps of these drainage paths and tentative ice margin positions, see Ford amd Geddes (pdf version available here).

Location of some of the key sills determining the glacial drainage of Algonquin Park.

Thus for hundreds of years, proglacial Lake Algonquing drained down the Petawawa River valley by various routes. For most, and perhaps all, of these routes the flow was over the Mink Lake sill. Although visually unimpressive, this sill played a key role in determining the current topography of eastern Algonquin Park. The present (quiet) state of the Mink Lake sill is shown below.

The Mink Lake Sill between Mink Lake and Cauchon Lake in Algonquin Park

(photo by Diana: 2014-06-25 - map - explore

The Cauchon Lake end of the portage into Mink Lake. The portage goes up and over the sill although it does not appear to actually go over the "saddle point" (the lowest point on the divide between the Amable du Fond River and the Petawawa River). The saddle point is a few tens of meters east of the portage and while lower, is not appreciably lower. Further, if — as Harrison suggests — 25 feet of water was flowing over this sill, the exact location of the absolute low point is of minor importance.

Mink Lake in Algonquin Park

(photo by Bob: 2014-06-25 - map - explore

Mink Lake at the end of the portage. All is tranquil now. When the sill was active, the view here would have been out over an arm of Lake Algonquin with very fast water in the foreground. It wouldn't have been possible to take a photograph from this location.

The Mink Lake Sill between Mink Lake and Cauchon Lake in Algonquin Park

(photo by Diana: 2014-06-25 - map - explore

The start of the portage from the Mink Lake end — small rocks and sand.

The Mink Lake Sill between Mink Lake and Cauchon Lake in Algonquin Park

(photo by Bob: 2014-06-25 - map - explore

Along the portage near the high point. Note the boulder pavement, consistent with a high current that washed away the smaller rocks.

The Mink Lake Sill between Mink Lake and Cauchon Lake in Algonquin Park

(photo by Diana: 2014-06-25 - map - explore

Near the Cauchon Lake end of the portage, it drops to lake level through a small gully. We presume, but don't know for sure, that this gully is natural and not man made.

The Mink Lake Sill between Mink Lake and Cauchon Lake in Algonquin Park

(photo by Bob: 2014-06-25 - map - explore

To our nonexpert eyes, the gully appears to be through fractured bedrock rather than piled waterborne rocks. Indeed, without a bedrock spine, one would expect that the sill would have been completely washed out. But weak portions of the bedrock might have been washed away.

Cauchon Lake in Algonquin Park

(photo by Bob: 2014-06-25 - map - explore

The high hills a the north shore of Cauchon Lake at its western end. High hills fairly tightly border the Petawawa drainage to the north all the way down to the vicinity of Montgomery Lake. Beyond Montgomery Lake, the river was able to expand to the north and create a delta in the Champlain Sea — the Petawawa sand plain.


  1. I am unable to unambiguously identify the location of this esker. Map P.2608 included in Ford and Geddes, show two eskers; one southeast by east of Carl Wilson Lake near the mouth of the river (and responsible for the lower two portages on the river) and one southwest of Carl Wilson Lake (near the campsite upstream of Perly dam). The former esker is cut by the river whereas the second seems to end at the river.

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L.J. Chapman and D.F. Putman (1973); The Physiography of Southern Ontario, Second Edition, University of Toronto Press.

M.J. Dadswell (1974); Distribution, Ecology, and Postglacial Dispersal of Certain Crustaceans and Fishes in Eastern North America, National Museum of Natural Sciences, Ottawa, Publications in Zoology, no. 11. (as quoted by Ford and Geddes)

Nick Eyles (2002); Ontario Rocks, Fitzhenry & Whiteside.

M.J. Ford and R.S. Geddes (1986); Quaternary Geology of the Algonquin Park Area, Ontario Geological Survey, Open File Report 5600. (online pdf)

Friends of Algonquin Park (undated); Barron Canyon Trail Guide.

J.E. Harrison (1972), Quarternary Geology of the North Bay — Mattawa Region, Geological Survey of Canada, paper 71-26.

Clyde C. Kennedy (1970), The Upper Ottawa Valley, a glimpse of history, The Renfrew County Council.

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