The tremendous power of lake ice
Ice is a marvelous form of our most precious resource. We depend on it for winter fun, and our lakes depend on it for their natural seasonal cycles. Despite the joy we get from frozen lakes in the winter, the ice can also wreak havoc on lakeshore by pushing up the sand and soil into large ridges.
Today I will talk about the tremendous power of lake ice, and the phenomenon called “ice heaving” or “ice-jacking”. There are some positives and some negatives to this phenomenon, depending on your perspective. It can be extremely damaging to personal property on the lakeshore, but it can also be beneficial to the lake’s health and its ecosystem.
First of all, why do these ice ridges form? Ice is not stagnant in the winter once it forms. It is continually changing, expanding and contracting as the temperatures rise and fall. When the temperature drops the lake ice contracts, producing cracks which refill with more water and freeze. Then, when t he temperature rises the ice expands, but there is no where for the ice to go in the lake so it pushes up against the shore. As ice continues to expand and contract throughout the winter, it produces a ratcheting effect. Each subsequent and cumulative push exerts tremendous pressure upon the shore.
For example, for a lake that is one mile across, when the ice’s temperature rises from 14 to 32 degrees Fahrenheit, the ice sheet will expand laterally a total of approximately 32 inches, almost 3 feet! This can occur in a matter of hours when there is no snow cover on the ice sheet.
Ice jacking is more severe in years where the temperatures fluctuate greatly and where there is little snow cover to insulate the ice and keep the ice temperature constant. This year, we have had a relatively thick snow cover all winter, so in theory, the ice heaving should be less dramatic.
There really isn’t much you can do on shore to keep the ice at bay. The ice so pow erful that it is impractical, from an economic standpoint, for the average individual to construct retaining walls or a foundation of sufficient strength to resist it. Rip-rap is of little value unless laid on a properly placed gravel foundation and on an extremely flat slope.
The safest course for lakeshore property owners is to follow setbacks and be sure that the buildings are located as high above the lake level, and as far removed from the shore as practical. Setback regulations of 100 feet from the shoreline are not only important for aesthetics and to prevent runoff into the lake in the summer, they also protect lakeshore property owners in the winter from ice damage. There have been years where ice can rip cabins near shore off their foundations.
What can property owners do in the spring when they’re left with large ridges of sand and soil? Usually, a DNR Public Waters Work Permit is required for altering shoreline below the ordinary high-water level. There are some conditions where you can grade and remove an ice ridge without a permit. Check with the DNR to be sure: 1-888-646-6367 or http://www.dnr.state.mn.us/permits/water/needpermit.html.
So what are the benefits to ice heaves and ice jacking? Ice heaving has been a natural process occurring on Minnesota lakes for thousands of years. The ridges form a natural barrier to runoff and traps nutrients from flowing into the lake. These nutrients then become fertilizer to plants that grow to form a buffer on the lakeshore. The shade and habitat offered by near-shore plants benefit organisms along the shore and in the lake, thus supporting nesting and spawning fish. If you have undeveloped natural shoreline, leave the ice ridges in place and watch in future years how they develop into great habitat.
Winter in Minnesota comes with its pluses and minuses, but for most of us that spend the winters here, the positives of winter fun on the lake ice out weigh the negatives of the ice’s power. To learn more about lake ice visit http://www.dnr.state.mn.us/waters/watermgmt_section/pwpermits/ice_ridges.html
Until next week, enjoy the lakes!
(Moriya Rufer is the Lakes Monitoring Program Coordinator for RMB Environmental Laboratories in Detroit Lakes, 218-846-1465, firstname.lastname@example.org.)