THIN ICE
Yellowstone Lake starts freezing later

YELLOWSTONE NATIONAL PARK (AP) - For the second winter in a row, Yellowstone Lake had thin ice and open water this year when it historically should have been frozen solid.

"It's phenomenal. We just don't know the reason why," Dan Reinhart, Yellowstone National Park's lake resource manager said.

Log books from the lake's ranger station show the lake usually freezes over in late December and remains covered with a solid layer of ice until May, Reinhart said.

But the last two years have been different.

"Usually you could drive a truck across the ice this time of year, but now no one wants to ski out there and cut a hole in the ice to check the thickness," said John Lounsbury, Yellowstone Lake district ranger.

During the winter of 1997-98 the lake froze over Dec. 26 but thawed a week later, leaving open water in the lake's northern body for another month, Reinhart said. The lake refroze Feb. 10.

"When I first heard them I thought they were hallucinating and thought maybe it was an optical illusion or a cloud shadow," Lounsbury said.

Still, he decided this winter to send rangers to an overlook to map the ice.

They discovered Yellowstone Lake had open water until Jan. 26, roughly a month later than usual, Reinhart said. The lake's surface is now frozen.

Lounsbury said discussions with retired rangers and winter caretakers lead him to believe similar open water has been seen only twice in the last 45 years.

Park officials have not determined the cause, but Jim Ruzycki, a park fisheries biologist, said there will be monitoring. Park biologists plan to double the number of thermometers in Yellowstone Lake as part of a fisheries study, and also hope to get an understanding of the lake's freezing patterns.

"It's probably due to global warming. It really doesn't take much of an increase, only a degree or two, to push back the freezing date by a month," Ruzycki said.