Nastapoka arc

Circular arc along the Hudson Bay coastline

The Nastapoka arc is a curved segment of the southeastern shore of Hudson Bay in Quebec, Canada, that extends from the most northerly of the Hopewell Islands to Long Island near the junction with James Bay. It is a prominent, near-perfect circular arc, covering more than 160° of a 450-km-diameter circle. While the circular shape has led to suggestions that it represents an impact crater, there is no evidence for this hypothesis, and it is thought to have been formed as a result of lithospheric flexure during the Trans-Hudson orogeny.

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