Ottawa-Bonnechere Graben

The Ottawa-Bonnechere Graben is a broad rift valley in eastern Canada, extending from near Montréal through Ottawa toward Lake Nipissing as part of the Saint Lawrence rift system. Formed when a block of crust dropped between the Mattawa and Petawawa faults, it is interpreted as a failed arm of the ancient Iapetus Ocean, later reactivated during the breakup of Pangaea. Erosion removed much of its volcanic record, but volcanic pipes, batholiths, dikes, and related features remain. The graben also shaped major travel routes: after the last ice age it became a spillway and later a natural corridor for rivers, voyageurs, railways, and the Trans-Canada Highway.

Ontario · Canada