Ice may look safe for a game of pick-up hockey on the lake, but as a new study out of York University found, looks can be deceiving. Warming winters are not only affecting ice thickness and timing - when a lake freezes and thaws - but also quality, making it potentially unstable and unsafe. When lakes and rivers freeze, there are two predominant layers of ice, what's called white ice and black ice. White ice is generally opaque, like snow, and filled with more air bubbles and smaller ice crystals, diminishing its strength and stability, while black ice is clear and dense with few air pockets and larger ice crystals making it a lot stronger. "Ice quality is important because of its direct implications for load bearing capacity for human safety and also how much light will transmit under ice for life under frozen lakes," says York Professor Sapna Sharma. The problem, says lead author and York Postdoctoral Fellow Joshua Culpepper, is that the unpredictable and warmer winter weather is creating thinner layers of black ice and sometimes a corresponding thicker layer of white ice, the unstable kind. The two combined can make for treacherous conditions for skaters, hockey players, snowmobilers, ice anglers and ice truckers. "We know that in general, lake ice is forming later in the season and breaking up earlier, which implies an overall shorter duration of ice cover, but our study looked at what the ice is doing. How is it changing? You might get periods of time when people are on the ice and they think it's safe, but it really isn't. It's not sufficiently thick enough given the changes in the quality," says Culpepper. The paper, "Lake ice quality in a warming world," was published today in the journal Nature Reviews Earth and Environment. Thickness alone is no longer a good predictor of safe ice. If there is too much white ice and not enough black ice, the ice may not be strong enough to hold a person's weight. It's what the... |