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The measuring points are located along the lake’s “sail line,” the route navigated by the towboats.
The men are looking for two types of ice. Blue, or black ice, is compressed and solid and harder to break through. White ice results from thawing and freezing cycles and as a result, holds air bubbles that make it softer.
“This is all blue ice,” VanGuilder said. “We won’t be seeing any white ice until later.”
The Corps does not have an ice-breaking ship for the Mississippi — being heavy craft, it would be difficult to navigate the ship through the 9-foot-deep channel used by the towboats.
Typically, shippers like to see ice less than 20 inches thick before trying to break through to St. Paul, though the first towboat last year smashed through a barrier 22 inches thick. The ice is broken by using an empty barge followed by a string of loaded barges to give it the extra oomph to plow through.
On this bitterly cold February morning, as VanGuilder pulls the measuring rod from the hole, a seasonal ritual he will repeat many times in coming weeks, he is asked half-jokingly if he can detect any sign of spring from beneath the ice shelf.
“Definitely not,” he replied, wryly.
Jim Anderson • 651-925-5039 Twitter; @StribJAnderson