I was following the boarder of the US and Canada on Google Maps, because, and found these interesting circular patterns of islands near the Northwest Angle. I have heard of geologic folding but I have never heard of Swirls or Circles. What is the cause of this?

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Swirl of islands on Google maps

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    $\begingroup$ Imagine a fold. Then tilt it so that it's axis is no longer horizontal. Then cut a horizontal slice through it. That would be my guess as to what is happening here. $\endgroup$
    – bon
    Commented Jun 4, 2017 at 18:48
  • $\begingroup$ I have edited your question to include a screenshot. Your second link was an extremely zoomed-in version of the first location on which no swirls were visible; I have removed that. $\endgroup$
    – Jan Doggen
    Commented Jun 30, 2017 at 15:34

1 Answer 1


Near the Lake of the Woods, the island swirl or vortex is due to structures in bedrock beneath the lake. The rocks in this area are old and have been folded by tectonic action. The area has either been folded into a dome or a basin, exposing different layers of bedrock. Glacial activity afterwards has 'flattened'the area, and differential erosion within the folded area formed valleys that flooded where the rock eroded faster.

Geologic history of The Lake of the Woods.


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