Last week's cold snap helped form a lot more ice on Lake Superior — but access to the well-known mainland ice caves at Wisconsin's Apostle Islands National Lakeshore remains closed.

In 2014 and 2015, the spectacle drew tens of thousands of visitors who walked a mile or more on frozen Lake Superior to reach the ice formations. But they haven't been open to foot access since then because of warm winters and poor ice conditions.

Julie Van Stappen, chief of resource management at Apostle Islands National Lakeshore, said the ice that has formed so far this winter is jumbled and jagged, pushed by wind and waves; the park staff call it "shark fin" ice. Walk-in access to the caves is not open to the public until the park officially deems it safe.

Jumbled ice along the shore of Lake Superior near the Apostle Islands mainland ice caves, east of Cornucopia, Wis., as seen on Feb. 1, 2019. Photo:  Courtesy of Apostle Islands National Lakeshore

"Oftentimes that first ice that comes in is really not real good ice, and it's certainly not very easy to walk through," she said. "Then sometimes the best conditions are if that totally blows out, and you get new ice. And what you need for really good ice formation is cold but very calm conditions."

And there needs to be a lot of ice. Van Stappen said there needs to be ice from the South Shore all the way to Minnesota's North Shore, locking in the ice pack — otherwise wind and waves can continue to chip away.

"We have seen 3 feet of ice blow out overnight," she said.

Along with the many ice caves come giant icicles that dot the shoreline of the Apostle Islands National Lakeshore on Feb. 4, 2014 near Cornucopia, Wis. Photo: Derek Montgomery for MPR News 2014

Specially trained park rangers will be monitoring the ice conditions in the coming weeks to see if they'll improve enough to allow safe access. Updates are posted on the park website and Facebook page.

To read more of this story, hear an audio report and see related stories, follow this link to the MPR website.  https://www.mprnews.org/story/2019/02/03/apostle-islands-ice-caves-update