NABSQNO 16T-541282-5155686

NABSQNO 16T-541282-5155686.NABSQNO 16T-541282-5155686.
The Grand Portal, Alger County, Michigan
Photos by David Brown

NABSQNO 16T-541282-5155686. The Grand Portal is a sea natural arch eroded through a promontory of Munising Formation sandstone. It is located on Lake Superior along the coast of Michigan's Upper Peninsula and is one of the many attractions of Pictured Rocks National Lakeshore. Access is via commercial boat tours out of Munising, Michigan. It is listed in the Vreeland catalog as number 14-4. Vreeland reported a span of 30 feet and a height of 8 feet in 1975. Since then, wave action and gravity have enlarged the height of the opening significantly, but not the span.

Interestingly, the present arch is all that remains of a much larger and complex double arch. It was this larger arch that originally received the name "Grand Portal." The larger of the pair collapsed in 1900, leaving the smaller to continue a cycle of rapid enlargement and eventual demise so typical of this type of natural arch. Here is an historical account of the 1900 collapse.

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© 2003 by Jay H. Wilbur and David Brown, All Rights Reserved.