Along the Great Lakes shoreline there is evidence of how dangerous these vast inland seas could become in a storm.
Shipwreck on North Manitou Island
Even with the guiding lights along the shoreline, many ships were lost. The Manitou Passage between the Manitou Islands and the shoreline of Michigan's Lower Peninsula was especially treacherous.
Portion of shipwreck in water near North Manitou Island
One clue that a ship (specifically, a steamer that burned coal) has gone down is the presence of coal washing up on land. Along the NW corner of North Manitou Island, I came across handfuls of coal mixed in with zebra mussel shells.
This wreck was recently exposed near Sleeping Bear Dune