Potholes at George Lake

Beaver in George Lake
A pothole complex, consisting of a series of partial potholes and a complete pothole, occurs in the side of a quartzite cliff at the western end of George Lake, in Killarney Provincial Park, Ontario. The complete pothole is located at the site of the small maple tree at the centre of the photo, immediately behind the swimming beaver. The pothole is about 2 m in diameter and of unknown depth, and contains some large rounded boulders. A series of partial potholes extends above and to the left of the pothole, to the top of the cliff. The pothole complex occurs on the lee side of a quartzite knob that was swept by currents flowing towards the southwest, which is towards the left in the photo.

Partial pothole in the upper section of the cliff
The upper section of the cliff contains a large partial pothole.

Partial pothole in the cliff
The photo shows a smaller partial pothole, about halfway up the cliff.

Detail of rock surface in the partial pothole
Detail of the rock surface near the base of the partial pothole shown in the previous photo, showing crescentic and circular marks in the rock surface. The crescentic marks are common in the quartzite rock along the northern shore of the lake. It is suggested they are relics of the disintegration process that caused the potholes during former catastrophic conditions. The crescentic marks represent "interrupted" pebbles and boulders that were in the process of being produced as the rock disintegrated.

Detail of the surface of quartzite
The photo above shows details of the surface texture of the quartzite at the site of the potholes. The rock surface was apparently in the process of disintegration, forming pebbles, resulting in potholes containing sand, boulders and pebbles, and the process was arrested. The erosion of the lake basin was easily accomplished by fast currents which removed the products of the disintegration. Loaded with this debris, the currents streamlined the exposed rock surfaces they impacted, and pebbles and boulders striated and grooved the streamlined rocks as they were swep away.

Pothole with George Lake in the background
The complete pothole and maple tree are at the lower right, below the climber. The rock in the foreground is quartzite. In the background is George Lake, which occupies a rock basin that was eroded by catastrophic currents flowing from the northeast to the southwest. Granite forms the opposite shore of the lake. The pothole complex is located on the lee side of the rock outcrop that was swept by the fast currents that eroded the lake basin. Pressure release during the excavation of the rock basin by the currents initiated in situ disintegration, causing the potholes. Disintegration also aided the erosion of the rock basin of George Lake, along with other similar lake basins in the region. Disintegrated material including pebbles and boulders was removed by the rapid currents. The currents were generated by uplift of parts of the Canadian Shield, when it was submerged.

Streamlined granite with striations
Streamlined rocks occur along the shores of George Lake, along with striations and grooves caused by the pebbles and boulders swept along as the lake basin was excavated by fast currents that flowed towards the southwest.  This photo shows a streamlined granite surface with striations, at the eastern end of George Lake. Striations probably obscured crescent shaped markings caused by rock disintegration in many areas.

Striations on a streamlined surface - another view
Another view at the same location as the previous photo, showing striations on the upstream side of the streamlined rock. Current flow was from northeast to southwest (towards the viewer).


Kor, P.S.G., Shaw, J., and Sharpe, D.R., 1991. Erosion of bedrock by subglacial meltwater, Georgian Bay, Ontario: a regional view. Canadian Journal of Earth Sciences, 28: 623-642.


Mystery of Pothole Origins
On the Interpretation of Potholes

Peculiar Potholes at Lion's Head
Streamlined Rocks
A Human Figure in Quartzite

Copyright © 2003 by Douglas Cox

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