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Wild Side: Strange but familiar forms of water

Sastrugi — snow dunes and holes shaped by the wind on our prairie. (Photo by Dan Wilcox)

H2O is a quirky molecule. Among its unique characteristics are multiple phases; solid, liquid, gas with rapid phase changes during minor changes in temperature and pressure. Under certain conditions, water vapor condenses and freezes into hexagonal snowflakes with delicate fractal patterns. Water has lower density when frozen than when liquid. It releases heat when freezing and has multiple forms of ice.

It’s a wonderful thing that water expands a bit before it freezes. We’re really lucky that ice floats or lakes and oceans would freeze from the bottom up and the world would be a harsh place.

Many houses around here are festooned with icicles from the Feb. 20 storm. Icicles form when liquid water drips down and freezes. Water flowing over the surface of an icicle freezes and some drips down from the tip. The tips of icicles aren’t pointed but have a small downward-facing cup shape. Water freezing on icicles releases heat, warming the air surrounding the icicle resulting in a wider base and a narrow tip where it is colder. Physicists are having fun investigating the processes of icicle formation.

University of Toronto physicists Antony Szu-Han Chen and Stephen Morris grew icicles in their laboratory. The surface of icicles formed in still air with pure water tend to be smooth and the icicles tend to branch with multiple tips. They found that adding impurities like salt to the water results in concentric rings around icicles.

Kazuto Ueno of the University of Quebec in Chicoutimi found that the ring-like ripples on the surface of icicles are about a centimeter apart, regardless of water flow, temperature and air flow. In Morris’s experiments, these ripples appear to crawl up the icicle as new ice is added. The physicists aren’t only having fun growing icicles. They are looking for ways to reduce damage to structures and power lines that occurs during ice storms.

The new snow from the Feb. 20 storm was blown around by the strong wind on Feb. 21, forming fantastically-shaped drifts and dunes in open country. The scene up on the hill at our place looked like the Arctic with wind-blown snow piled in patterns reminiscent of waves on the ocean. These patterned snow dunes and holes are called sastrugi, after old Russian words meaning to plane or shave down wood.

Wind erodes snow from the upwind side of an obstacle. The snow particles dance over the surface like sand on dunes or in rivers in a process called saltation. The snow deposits in the lee of the obstacle, forming the wave-like patterns.

We are starting to feel like sastrugi, blasted and planed down by blowing snow. Our faces are red from being outside; not so much from being tanned by the sun. This winter we’ve experienced temperatures well below average, ice particles blowing in the wind and forming rainbow parahelia around the sun. Now that the meteorological winter is over and the sun is giving us more heat, we can expect that the winter will relent sometime soon. Enough of this polar vortex!

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--by Dan Wilcox, outdoor columnist