Mary Blickenderfer, University of Minnesota Extension, 888-241-0885

Answer: Due to lack of snow cover, we anticipate a “bumper crop” of both this year!

It’s still winter 2007, but shoreland professionals are already anticipating a flood of phone calls this spring from shoreland property owners wanting to know what to do about the mountainous soil ridges (“ice ridges”) along their shoreline and the dense mat of “weeds” floating on their lake. Let’s take a closer look at both…

Ice ridges form when a moving ice sheet pushes up soil along a shoreline – much like a bulldozer. This can happen during a single, spring “ice-out” event or less noticeably as an ice sheet freezes and gradually expands throughout the winter. Anyone who has experienced frozen water pipes understands that water expands as it changes from a liquid to a solid. Similar forces may arise as our lakes freeze. In addition, a rise in air temperature during a typical winter day (or an approaching warm air mass) will cause the ice sheet to expand slightly, exerting a force outward. Then, as the air temperature cools at night (or with an approaching cold air mass) ice will contract, but it lacks the internal (tensile) strength to shrink back to its original size. Instead it cracks under tension, often producing a gap along the length of the crack into which lake water will seep. As this water freezes it expands, exerting an additional force outward. Under these forces, ice will sometimes buckle in the middle of the lake, but most often the force of the expanding ice is transmitted to the surrounding shores.

During a typical Minnesota winter, deep snow insulates the underlying ice sheet from temperature fluctuations and the ice sheet expands very little. However, during winters of little or no snow cover, ice exposed to daily and other periodic air temperature fluctuations will expand, exerting 8 tons per square foot of force on our shorelines. What happens to our shorelines as a result of this force depends upon many factors; several are related to the level of shoreline development. Undeveloped shorelines often have small, natural ice ridges, but incur relatively little ice damage compared to that of developed shorelines where it is common to see overturned rip rap, retaining walls thrust into the air, whole slabs of lake sediment deposited onto lawns, and ice ridges two feet high (see the Ice Damage Photo Contest announcement in this issue). For information and resources on how to deal with ice ridges, see “It’s Rough to Have Ridges – Living with Ice Ridges on Your Shoreline” in the From Shore to Shore March-April 2006 issue (http://shorelandmanagement.org/downloads/mar_apr06.pdf).

Curlyleaf pondweed is an aquatic invasive plant species that was introduced to the U.S. in the 1800s and has since spread to many bodies of water. It has a unique life cycle. Sprouting in autumn from dormant buds, called turions, which lie on the lake bottom, the young plants remain alive under the ice during the winter, giving them a jumpstart on the native plants that remain dormant until spring. Their competitive advantage over native aquatic plants tends to be even greater in years of little or no snow cover because their growth is more vigorous due to the additional light they receive through the ice. If you suspect curlyleaf pondweed is growing in your lake, you should consult with your local or regional Minnesota Department of Natural Resources fisheries office.

Posted in Plants, Care of Shoreland Property, Lakes |