Recent weather patterns of small amounts of snow, rain, freezing rain, ice and “wintery mix” have made going outside less enjoyable and downright treacherous. Rather than cursing the conditions, it is interesting to explore the science behind what creates the “glaciers” in our driveways.
True glaciers are fascinating and are responsible for much of our local topography. The landscape of New England is scattered with lasting “gifts” from the glaciers that covered this part of the world over 10,000 years ago. As the climate warmed and the ice sheets melted and retreated to the north, rocks of varying sizes and sediment that had been trapped in the ice were left behind. One example is giant boulders or “glacial erratics” that can be found throughout New England (Madison Boulder and Pawtuckaway State Park provide fabulous specimens). Imagine the force required to move rocks the size of cars, or even houses!
The weight and movement of mile-high glaciers also carved out basins, creating lakes as meltwater and precipitation filled the depressions. New Hampshire’s largest body of water, Lake Winnipesaukee and our deepest one Newfound Lake were both formed by glacial activity. Smaller bodies of water were formed when huge blocks of ice broke off from glaciers and were buried under sand and gravel deposits. As the ice melted, the sand and gravel settled beneath the melting water forming “kettle ponds.” Lake Chocorua in Tamworth is classic example of a kettle pond.
Other remnants of the glaciers include striations on the tops of mountains. These scratches on peaks such as Mt. Kearsarge in Warner, Mt. Monadnock in Jaffrey and Blue Job in Rochester, were formed by the grit in the receding glaciers scoring the underlying rocks.
Alpine glaciers are also famous for creating U-shaped valleys as great layers of ice carve into mountains. These contrast with V-shaped valleys that are formed by the eroding waters of flowing rivers. I first saw an example of this at Mt. Rainer in Washington state where we stood at the base of a valley and looked toward the glacier near the mountain top. The valley sides were curved and … U-shaped, just like I’d learned about in geology class. Closer to home, Franconia Notch in the White Mountains is an example of a glacially carved, U-shaped valley.
What does all of this have to do with the ice in our yards? Before the rain came, I noticed that some of the snow that was in our driveway was transforming into ice. How does that happen? On a gigantic level, glaciers are formed by the weight of snow compacting itself. When snow is compressed, individual flakes become smaller, rounder and thicker, changing to granular snow and eventually into ice crystals as air spaces are reduced. On the micro level, our cars compress the snow (it was not deep enough to plow or snow blow, so we just drove over it) and do the same thing, creating ice. Obviously, the ice that formed in our driveway is not at the scale that reshapes terrain, but the basic process is the same.
When ice forms in places where we don’t want it, there are options for eliminating it. Salting our roads and driveways is a common practice. Adding salt reduces the freezing point of water by causing a chemical reaction that blocks the formation of the molecular bonds that transform liquid water into solid ice.
However, salt can cause damage to plants, infrastructure and water quality so may not be ideal in all situations. Another option is to wait for weather to warm and melt the ice. That may not be practical since winter temperatures often stay below freezing for extended periods. Yet ice and snow can be reduced by sublimation. That is the process when a solid becomes a gas without going through the liquid stage. This happens more frequently when humidity is low and/or it is windy this process has helped reduce the ice in my yard.
Of course, warm weather will eventually come, and the snow and ice will disappear from our driveways and walkways. In the meantime, take it slow on the ice and appreciate the science that creates it and the processes that make it go away.