Published April 30, 2010, 12:00 AM

Apostle Islands rock arch collapses

The Apostle Islands National Lakeshore has lost one of its scenic landmarks. The Hole-in-the-Wall rock arch on the northeast corner of Oak Island collapsed sometime over the winter.

By: Steve Kuchera, Duluth News Tribune

The Apostle Islands National Lakeshore has lost one of its scenic landmarks. The Hole-in-the-Wall rock arch on the northeast corner of Oak Island collapsed sometime over the winter.

“Weathering and erosion are part of the story of the Apostle Islands,” said Neil J. Howk, the national lakeshore’s assistant chief of interpretation and education. “The fact that the shorelines are constantly changing is one of the things that makes the place pretty interesting to start with. This is a real dramatic example of the types of changes we can see here.”

A park worker found last week that the arch had collapsed over the winter. The arch was composed of an isolated rock precariously seated between two joint cracks. It was located within the Chequamegon Sandstone formation.

“It’s a little bit different than the Devil’s Island sandstone that forms the really extensive sea caves,” Howk said. “Most of the caves and arches are found in the Devil’s Island formation. That is one of the things that made Hole-in-the-Wall somewhat unique — it was one of the few big arches we had in the Chequamegon Sandstone.”

Lakeshore officials never have counted how many arches are found in the Apostle Islands.

Water erosion from wave action forms sea caves and arches. And while Lake Superior has been at its current level for 2,500 to 3,000 years, the Hole-in-the-Wall perhaps existed for no more than 100 years.

“Before that, it was a wall,” Howk said. “We see old postcard views and, unless it says, we have no idea which island it was taken of because the shorelines have changed so much in 100 years.”

The Hole-in-the-Wall is not the first arch to collapse within historic times. Near the north end of Hermit Island is a pile of rocks used by roosting gulls and cormorants.

“One hundred years ago that was an arch,” Howk said.

Howk reminds visitors to use caution when hiking or boating near the park’s eroding shorelines.

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