Sawyer County, Wisconsin
Numerous reports of large ice heaves on many lakes in Sawyer County.
Riders- use extreme caution when lake riding as these ice heaves can be difficult to see, and they can pop up anywhere at any time.
Stay on the marked snowmobile trail – even then, be watchful as new heaves can occur anytime.
NO ICE IS EVER CONSIDERED SAFE- Riders, YOU ARE RESPONSIBLE for your safety on any frozen lake! Adjust your speed during low-light or low-visibility conditions – so you can easily avoid dangerous obstacles or areas.
REPORT: Within the last week or so, our Alliance has gotten several reports of substantial ice heaves on many of our lakes. In a normal winter, we might hear of an occasional ice heave- usually on the larger lakes of Round and Lac Courte Oreilles, but this year they are all over!
How do these ice heaves or pressure ridges form? I found a lot of articles about ice heaving, but the most useful information came from the Minnesota DNR website. Below I’ll summarize what I found:
Ice heaves are a natural occurrence due to ice constantly expanding and contracting from fluctuating temperatures- there are other causes, such as wind, where springs are, lake depth and currents, but temperature fluctuation seems to cause the most action. On some lakes, ice heaves can occur in the same area each year- almost like there is an earthquake ‘fault line’ in the lake.
Dropping temperatures force the ice to contract, creating cracks in the ice sheet, which fill in with lake water and eventually refreeze.
The warmer days or periods with rapidly fluctuating temperatures cause the ice to expand. If the ice sheet is well anchored to the shoreline, it has nowhere to go but up- creating the classic ice heave. Sometimes the sheet will expand towards the shoreline and take out whatever is in its path, including buildings, docks and trees. Powerful shifting ice is known to create berms along shorelines that remain after the ice is gone – commonly seen on some of Lac Courte Oreilles’ shorelines.
During expansion, tremendous pressure breaks the ice sheet in two and both sides move upwards, gnashing against each other as if they are each fighting. One ridge may end up higher and over the other ridge, and oftentimes lake water escapes from the lower ridge side.
Some websites offered complicated scientific formulas to estimate ice movement during expansion. I was looking for just a simple example though and found the same one across a few websites: an ice sheet on a lake that is a mile across needs to expand about 3 feet.
Why are we seeing so many this year? Just about every article I read mentioned that ice-heaving is more prevalent when there is no snow covering the ice sheet- sounds like our winter so far! Snow keeps the ice insulated and the temperatures consistent, minimizing ice heaving. Bare ice soaks up warmth from the sunlight and wind- perfect conditions for expansion and heaving.
Are these ridges dangerous? They are if you hit one! Pedestrians and slower-moving vehicles should be able to easily avoid ice-heaves, but those on faster vehicles, like snowmobilers, may not see an ice heave until they are right up to it- which is too late. Snowmobilers should stay on the staked lake trails but still need to be cautious as ice ridges can form anywhere, and suddenly.
The Wisconsin DNR reminds everyone that frozen lakes are never considered safe-always check with local sources on ice depth and conditions before you venture out onto a frozen lake.
There is a report from Kevin at Revelles on Nelson Lake, of a substantial ice heave out from Hard Rock Circle. See the Alliance post below.
https://www.facebook.com/share/p/19pHyjV3k4
This one on Nelson Lake extends pretty far out toward the snowmobile trail in the center of the lake, but so far, is not yet affecting the path marked for snowmobile travel- if riders venture off trail though, they may run into this heave.
Riders- just use caution on the lakes and watch for ice heaves, and other dangers, such as plowed paths on the lake- both of these can be difficult to see until right on them- and both are quite dangerous if you hit them.
The picture is from Kevin at Revelles- I zoomed in to show details of the ice heave.
