With the recent extended warm spell, safety on frozen lakes and sloughs should become a concern. While some look at melting ice as a sign of spring and warmer weather, for winter outdoor enthusiasts, it is a sign that our season is winding down. As Winter ends, the need for safety becomes even more important for those trying to enjoy it as long as they can.
Ice Formation & Color
To understand how ice melts, it helps to know how it formed in the first place. When ice forms, it does so in layered segments called candling. Thawing is the process of ice decay. During thawing ice does not shrink, it hollows out. The process of hollowing out is referred to as “Honey Comb”. As the ice hollows out, the honey combs either fill with water and refreezes or not, or they remain hollow. The process of hollowing out and filling or not helps to create the appearance of grey or black ice.
Ice color can be a clue in helping to decide on the safety of ice; it cannot, however, be the sole indicator.
- Oily to Opaque: Crystals are formed into clumps – Low strength, Stay off.
- Light Grey to Dark Blue: Melting Ice – Density can’t support load, Stay Off.
- White to Opaque: Water-saturated snow freezes on top of ice, Poor to fair.
- Blue to Clear: Freezing water formed over a long period. High density, very strong. Safest using thickness suggestions for various modes of use.
Thickness, Strength, & Thawing
Ice thickness and ice strength are not one and the same. The conditions that formed the ice have a bearing on the strength of the ice.
Ice formed early in the season is stronger than ice formed later in the season. The ice that formed late in the season is often referred to as “rotten ice” and is weak. Because it has structurally been changed through the melting process, formed by melting snow, refrozen, or made by water bubbling up through cracks and freezing, this ice is considered weak no matter how thick it becomes. Slush weakens ice and indicates that it is no longer freezing from below.
Thawing of Ice occurs in four ways:
- Top surface melting. This melting is strongly driven by wind.
- Internal melting. Driven by sunlight and results in relatively slow loss but can dramatically weaken ice.
- Under ice melting. Caused by turbulent currents in the water underneath. In shallow water, this can be increased as the sun heats the water underneath.
- Wind driven rafting. When the wind is strong enough to push the ice over itself.
When going out on ice that is in its later stages there are some safety precautions to follow:
- Check with locals about the ice conditions.
- Take a “spud bar” or ice chipper and check conditions as you go. Cold ice comes out in thin, conchoidal chips. Warm ice comes out in little chunks in small grain ice and bigger ones for large grain ice.
- Use a drill. Drill a hole in the ice to about three inches from the bottom and remove the shavings. See how fast the hole you created fills with water. If the hole fills in less than 10 seconds, the ice is in the later stages of thaw. You may also notice in later stages of thaw the ice comes off as chunks when drilling rather than shavings.
- Many of the safety precautions for early season ice apply to late season ice also. Carrying ice picks and wearing a personal flotation device (when on foot) are things that may be able to help you in case of an issue.
Source: South Dakota State University