Why is my shoreline damaged?
Editor's note: The following is a Minnesota Department of Natural Resources (DNR) "Question of the Week."
Q: It's not uncommon for lakeshore property owners to return to their cabins in the spring to find damage to their shoreline, retaining walls, docks and boat lifts, and sometimes to the cabins themselves. What causes this?
A: This type of property damage is caused by "ice heaving" or "ice jacking." As ice freezes and thaws, cracks form because of the different contraction rates at the top and bottom of the ice sheet. This is especially true in years when there's a lack of insulating snow cover. When the water rises in the cracks and freezes, the ice sheet expands slightly. Rising air temperatures warms the ice, which causes the additional expansion to exert a tremendous thrust against the shore. This powerful natural force forms a feature along the shoreline known as an ice ridge. These ridges can sometimes reach as high as five feet or more. Additional warming and cooling of an ice sheet can cause additional pushing action that possesses enough power to nudge bridge masonry piers out of plumb and push houses off their foundations.
For more information about ice ridges, go to: http://files.dnr.state.mn.us/publications/waters/shoreline_alterations_i...
-- Jim Solstad, DNR hydrologist