Okay, so snow came a little early this year and hopefully it won’t stick around until spring, but it’ll be here to stay, sooner or later, so let’s get to know snow.
Believe it or not, snow is a good thing in the garden. Under the winter’s collection of fallen snow, there is a secret world where small animals and insects spend the long, cold months dozing and foraging for food. This is the pukak layer, where it is always around zero degrees. Here, the heat of the earth has risen to the surface to melt and crystallize the snow, leaving gaps that can be turned into underground highways for the denizens of the pukak, which is the name for this layer.
Voles and mice and beetles use this highway, building air vents to the surface every so often to allow carbon dioxide to escape. Sadly, this also signals their presence to predators that lurk near the vents waiting for dinner.
They say every snowflake is different, but while that may very well be true for larger, more complex snowflakes, it is doubtful when it comes to the microscopic simple crystals which form in the coldest weather.
Snowflakes are really condensed water vapour which freezes directly into ice crystals. The simplest snowflake is a hexagonal prism, with a top and a bottom (basal facets) and six sides (prism facets). Snowflakes also form as hexagonal lattice crystals. As the snow crystal moves through the air, it tends to collide with objects, which causes a bump to form, usually at the corners first. These bumps then pick up new water molecules causing the bump to “grow” into branches. The branches pick up bumps and grow into side branches and so on. The final shape and how the branches form depends on temperature and humidity.
Do you love that sound of snow under your feet on a cold winter morning? If the temperature of snow is warmer than -10 degrees C, it will not squeak when you walk on it. This is because the pressure of your footstep partially melts the snow, allowing water to flow under your footfall. When the snow is colder than -10 C, the pressure from your weight crushes the ice crystals beneath your boot making that squeaking, or creaking, sound.
There are many types of snow. Sometimes snow falls in little balls known as a graupel or a snow grain or, most commonly, as sleet. Rime ice, that white stuff that coats tree limbs, consists of balls of white ice that form when fog droplets freeze at -2 to -8 degrees C. Rime ice, similar to hoar frost, builds up on tree branches. Hard rime is difficult to shake off surfaces. Soft rime is feathery or spiky.
Rime ice on aircraft wings is dangerous because it disrupts air flow, decreasing lift and increasing drag. But aircraft can actually trigger snow when they punch holes in low clouds. Propellers cool air up to 30 degrees which can cause ice crystals to form. Wings on high speed jets can cool the air above the wings by 20 degrees, producing a stream of ice crystals behind the wings.
If you have noticed the silence after a fresh snowfall, is is because freshly fallen snow, has the power to absorb sound. The trapped air between the snowflakes reduces vibration, arresting the sound waves.
Light fluffy snow weighs in about five to seven pounds per cubic foot and contains about 2.83 litres of water or five-eighths to three-quarters of a gallon. The ratio of snow to water is about 12 to one.
Snow is a wonderful partner for the sun when it comes to reflecting heat and ultraviolet rays. Sun reflected on snow can scald the bark of thin-barked and young trees by heating and reactivating tree cells which then refreeze when the sun is gone causing the bark to split. This is why it is important to put up a shield against the March sun when you plant new trees, especially fruit trees which have thin bark.
Dorothy Dobbie is the publisher of Manitoba Gardner magazine, which is celebrating its 20th anniversary of continuous publication in 2018. If you would like to subscribe, call 204-940-2700 and Shelley will take you order. Or you can go to localgardner.net and subscribe on line.