The term “rotten ice” refers to ice that has lost its structural integrity through deterioration and is profoundly weakened, posing a severe danger to anyone attempting to walk or travel across it. Unlike solid, newly formed ice, rotten ice can fail suddenly, often without warning, even if it appears thick.
The Structure and Formation of Rotten Ice
Rotten ice develops when the tightly packed crystalline structure of solid ice begins to break down due to cycles of melting and refreezing, which is a process known as candling or rotting. This deterioration preferentially occurs along the vertical boundaries of the ice crystals, which contain impurities like trapped air, salt, or contaminants. As the ice warms, melting begins at these boundaries, creating vertical channels that fill with water.
This process forms what is commonly called a “honeycomb structure,” where the ice is composed of numerous vertical columns resembling candles clustered together. Because the structural weakness is vertical, the ice loses its horizontal load-bearing capacity. This means even several feet of thickness may not support a person’s weight.
The rotting can occur from the top, often driven by the absorption of solar radiation, or from the bottom, caused by warmer water currents or heat transfer from the underlying water body. Runoff from upstream melting, especially if it contains road salt or other contaminants, can also create “hot spots” that weaken the ice locally. The presence of an insulating layer of snow can also contribute to weakness by inhibiting the ice from thickening and insulating the surface from colder air temperatures.
Visual and Auditory Indicators of Unsafe Ice
Solid, strong ice is typically clear or blue-black in appearance, a sign of its density and purity. In contrast, rotten ice often appears dark, gray, or splotchy, sometimes taking on an opaque white or mottled look due to the presence of numerous air pockets and water-filled channels. If the ice is saturated with water, it may look transparent, deceptively resembling new black ice, but a spongy or wet texture on the surface is a visual indication of internal decay. Another telltale sign is the presence of “candle ice,” where the vertical columns become visible, sometimes making a clinking sound if they break apart and float in the water. Ice that has cracked or developed fissures has lost a substantial portion of its strength along those lines.
Auditorily, solid ice makes a loud, distinct “ping,” “groan,” or “talk” sound when stressed, providing a warning before a major failure. Rotten ice, however, will often fail without a clear sound, or it may produce a dull, muffled thud or a slushy sound underfoot. Before venturing out, it is wise to test the ice near the shore using an ice spud or a stick, paying particular attention to areas near docks, rocks, or flowing water.
Immediate Actions When Confronting Rotten Ice
If you are walking on ice and notice a sudden change in appearance, color, or sound, or if the ice cracks, you should immediately distribute your weight as widely as possible by lying flat. This action minimizes the pressure on the weakened ice, and you should then crawl or roll back along the path you used to get there, as that ice has already supported your weight. Do not attempt to stand up until you have reached a safe, solid area near the shore.
If you fall through the ice, the first response must be to control the initial cold shock, which can cause hyperventilation. To perform a self-rescue, immediately turn toward the direction you came from, keep your arms on the unbroken ice shelf, and use a strong flutter kick to propel your body horizontally onto the ice. If you have ice picks, use them to gain purchase on the slippery ice, continuously kicking your legs to keep your body as horizontal as possible. Once partially out, you must roll or army crawl away from the hole, spreading your weight evenly, until you are certain you have reached ice thick enough to stand on. If you witness someone else fall through, immediately call for help and use the “Reach, Throw, Go” approach, prioritizing reaching with a long object or throwing a rope before attempting to go onto the ice.