Monday, 16 March 2009

ICE: accidents waiting to happen

On a sad note: Muskoka's Carolyn Bray, and her daughter, have gone through the ice on Lake Rosseau and drowned. See, The Globe & Mail, CP24, 680news, Toronto Star, and, for more info.

Stay off the water and ice. OPP have warned us all. Pressure cracks are unseen and unpredictable. With extreme night and day temperatures we don't know what is happening under the ice. The ice crack, water pools on top, fissures form as the water drains down the cracks, and the moving water melts the ice, whose flow is unstable and unpredictable.

And still, today, I saw people on ATVs and snowmobiles. I wish they could watch the video in with the mother mourns her son. It is a grief we should not have to bear. The recent drownings have been a lesson.

When the ice melts into puddles snowmobilers like to splash through them. The problem is they do not know how deep the ice is at this point. Look for darkened layers as the ice becomes waterlogged, turns into crystal shards, and begins to sink. It shatters in the dark cracks. I remember in 2006, just before my mother died, I wrote in my journal: one day puddles formed, slowly the ice just sunk below the surface. One day it was there, that afternoon simply sank. A portent of doom. One day here, the next you are gone. The joy and anticipation of spring was marred by mom's cancer as she wasted away and fought the tumours. Cancer framed our lives for 4 years that she fought it. Death and grief change us forever.

During the warm days the water on the surface melts. It pools in lower areas. Overnight it refreezes and it is hard to spot as being weaker. A snowmobile can drive over it quickly, inertia keeps it moving, but something like a truck or ATV goes more slowly and is prone to sinking.
In places between islands the water flow is faster meaning the ice layer is thinner. At the shoreline meltwater seeps into the lake and causes breaks that heave and crack. Many people skirt the edges of the lake where the ice had thawed more quickly than in the middle.

Popular Mechanics writes
about ice bridges. When the truck moves over tfhe ice, it weighs it down and the water is displaced. This creates waves under the water that reach shore, and roll back. Speed is limited to 24 km/h to reduced this danger on ice roads.

You can spot places where there are cracks in the ice. In subzero night the ice shrinks, as it refreezes, and cracks. Layers of ice act like the land during an earthquake. One can be forced up on another. Once the ice begins to crack - which can be unseen while speeding over it, the ice is fragile. The wind continually pushes on the ice, forcing the water to heave, ebb and flow underneath causing further cracks. The underwater currents continue to flow. The water is a constant 4˚ C. all winter, unlike the land that stays at 0˚ C., at the surface under the snow.

In the photo of the ice beside the shore, you can see the darker parts. These parts melted, the chunks broke off, and we had some ice floes. At the edge of the ice, the leading edge begin to sink as they warm. You can see the ice in the header photo, with chunks floating.

At the shoreline I find that the small openings a puddles form small ice rinds over night. Each night the rinds are thinner and thinner. Lately, it's only been about 1 1/2", what with -2 ˚ C. temperatures. This thinner layer of ice melts again in the day time. It looks solid, but is very fragile. See this article on ice thickness. They suggest that 4" is required for 200 lb. (a person & gear), 5" for an 800 lb. snowmobile, 8" for a car. Unless you go out and test the ice, walk it and survey it you cannot be sure how thick it is.

  • Lakes and ponds do not freeze, or thaw, at the same rate and speed.
  • If something is sticking up from the ice, it will retain heat and melt a hole weakening the ice.
  • Travel slowly, as the speed of your vehicle can crack the ice and cause under water currents.
  • Single, unbroken pressure cracks are safer than smaller spider cracks. Walk slowly and carefully if you must be on the ice. The darker the ice, the more water content.


Judy said...

A lot of information! I knew the trucks on the ice roads had to travel at a prescribed rate, but I did not know why. I tend to be over-cautious of ice in general, and I dislike snowmobiles because they are noisy, so I am safe, but a lot of people are not, to the sorrow of those they leave behind.

Junosmom said...

That is very sad.