DULUTH – Ice coverage on Lake Superior is well below average so far this season, which likely means another year with no ice cave access along Wisconsin's South Shore.

"We're always hoping — it's a beautiful event we want people to be able to experience," said Justin Olson at the Apostle Islands National Lakeshore.

The last time the ice caves were accessible by foot was in 2015. Heading into the weekend, Olson said, "We have a lot of open water here."

On Friday less than 5% of Lake Superior was covered by ice; typically about a quarter of the lake is covered by the end of January.

Since 1973, when the National Oceanic and Atmospheric Administration first started tracking ice on the Great Lakes, only one winter had lower coverage on Jan. 31. That was in 2006, which had peak ice coverage of about 16% on Lake Superior — and no ice caves.

Ice is tracked for business as well as pleasure. The movement of cargo on the Great Lakes is so important that delays in icebreaking cost businesses $1 billion in lost revenue in the 2018 shipping season, according to the Lake Carriers' Association.

A group of U.S. senators, including both of Minnesota's, recently sent a letter to the Trump administration asking for a new icebreaker for the Coast Guard.

A University of Michigan study last year also said tracking ice on the Great Lakes is "an ideal case study" for climate research. The study's authors said that climate change's impact on the Great Lakes would be a "future punctuated by high variability."

Ice surrounding the Bayfield Peninsula, where the ice caves form, was more consistent before 1997, according to the research.

"For years, in the 1970s, 1980s and early 1990s, it was simply understood that, at some point in the season, the ice cover around the shoreline was going to form and was going to be consistent year to year," Andrew Gronewold, an associate professor and one of the study's authors, said in a statement. "In the late 1990s, all of a sudden we saw years in which there was no safe ice cover."

Ice coverage on Lake Superior typically peaks in February or March, though data show most winters with this level of ice on Jan. 31 do not accumulate much more. It has happened, however.

In December the federal Great Lakes Environmental Research Laboratory predicted Lake Superior would peak at 54% ice coverage.

Little ice is expected to build in the next week along the Apostle Islands National Lakeshore, which is celebrating its 50th anniversary this year.

"If it gets really cold and we don't get a lot of wind, who knows what can happen," Olson said.

Even when ice does coat the majority of the lake, as it did last year, the quality of the ice needs to support the hundreds of thousands of visitors the ice caves draw.

For updates on the ice caves, call 1-715-779-3397, ext. 3, or visit the Apostle Islands National Lakeshore on Facebook.

Brooks Johnson • 218-491-6496