Column: Natural Resource News: By Jody Derks
With ice forming on Minnesota lakes, outdoor enthusiasts may be tempted to get out before ice is thick enough to support foot traffic. The Department of Natural Resources offers a message — stay off the ice until at least 4 inches of new, clear ice is present. Ice thickness may vary greatly across a body of water, making it important to check the ice conditions before heading out.
Before heading out on the ice:
• Contact a local bait shop or lakeside resort to ask about ice conditions.
• Check ice thickness once you get there.
Temperature, snow cover, currents, springs and fish all affect the relative safety of ice. Ice is seldom the same thickness over a single body of water; it can be many inches thick in one place and an inch thick a few yards away.
The DNR offers the following guidelines for new clear ice:
• 4 inches for ice fishing or other activities on foot.
• 5 inches for snowmobile or ATV.
• 8-12 inches for a car or small pickup.
• 12-15 inches for a medium truck.
Many factors other than thickness can cause ice to be unsafe.
White ice or “snow ice” is only about half as strong as new clear ice. Double the above thickness guidelines when traveling on white ice. In addition to checking conditions be prepared with an ice safety kit. An ice safety kit should include:
• Ice picks
• Ice chisel
• Tape measure
Last, tell someone where you are going and when you expect to return.
Did you know?
New ice is usually stronger than old ice. Four inches of clear, newly formed ice may support one person on foot, while a foot or more of old, partially thawed ice may not.
Ice seldom freezes uniformly. It may be a foot thick in one location and only an inch or two just a few feet away.
Ice formed over flowing water and currents is often dangerous. This is especially true near streams, bridges and culverts. Also, the ice on outside river bends is usually weaker due to the undermining effects of the faster current.
The insulating effect of snow slows down the freezing process. The extra weight also reduces how much weight the ice sheet can support. Also, ice near shore can be weaker than ice that is farther out.
Booming and cracking ice isn’t necessarily dangerous. It only means that the ice is expanding and contracting as the temperature changes.
Schools of fish or flocks of waterfowl can also adversely affect the relative safety of ice. The movement of fish can bring warm water up from the bottom of the lake. In the past, this has opened holes in the ice causing snowmobiles and cars to break through.
The DNR ice thickness guidelines and more resources are available at www.mndnr.gov/icesafety.
Jody Derks a Fisheries Specialist for the Minnesota Department of Natural Resources.