said Tuesday of the large ice disk he witnessed Saturday. "You
looked at it and you thought, how did it do that?"
engineering background kicked in. He calculated the disk's
diameter to be about 55 feet, took photos and videos of it and
then turned to the Internet for more information about what he,
his brother-in-law and nephew had seen.
"It's not an unknown phenomenon, but it is relatively rare,"
said Loegering, who lives in rural Casselton, about 20 miles
west of Fargo.
Allen Schlag, a National Weather Service hydrologist in
Bismarck, and Greg Gust, a weather service meteorologist in
Grand Forks, said a combination of cold, dense air last weekend
and an eddy in the river likely caused the disk.
"It's actually quite beautiful," Schlag said.
The cold, dense air — the air pressure Saturday in nearby
Fargo was a record high for the city for the month of November,
according to Gust — turned the river water into ice, but since
the water was relatively warm it didn't happen all at once.
Floating bits of ice got caught in the eddy and started to spin
in a circle.
"It's not a continuous sheet of ice," Schlag said. "If you
were to throw a grapefruit-size rock on it, it would go through.
It's not a solid piece of ice — it's a collection of ice cubes."