2011-02-12 / Columnists

Nature Notes

Water: Think About How Much We All Depend On Its Various Forms
By Patricia Martin

Well, folks, it’s winter. The boats have stopped running, snow has fallen, and the ice has “made” (meaning that the ice bridge to St. Ignace has formed so we can cross). It got me thinking about water, and how much we depend on it in its various forms. Think about it, humans, in fact all living things, are largely made up of this simple molecule. An intake of water is necessary for all life, for respiration, transpiration, and for countless chemical reactions. Water is used for washing and cleaning, drinking, and cooling, and on Mackinac, water is used for transportation. Whether it’s crossing the Straits in a ferry, sailboat, or motorboat, crossing the ice on snowmobile, foot, skis, or bike (yes, people bike across the ice bridge), or simply getting around the Island in the winter on freshly-fallen snow using snowmobiles or cross-country skis, we use some form of water to get from here to there.

This winter again there has been a shortage of snow, along with a shortfall of rain last summer, in the Eastern Upper Peninsula. While other parts of the country were getting dumped on, most of the storms have gone north or south of Mackinac. We do have some snow, but not as much as we would like to make getting across the ice easier on our machines, or on the trails and roads for our skis.

Water, if it’s pure, has no taste, no color, and no odor. It freezes at 0 degrees Celsius (32 degrees Fahrenheit) and boils at 100 degrees Celsius (212 degrees Fahrenheit). These values are abnormally high for a compound with such a low molecular weight. As most of you know, water is composed of two hydrogen molecules and one oxygen molecule, in other words, H2O. Its maximum density occurs at 4 degrees Celsius, so that when water freezes at 0 degrees Celsius, it expands and is less dense than the water at 4 degrees Celsius. This allows ice to float and make an ice bridge, and why water pipes may burst when they freeze.

The crystalline structure of ice and snow. The crystalline structure of ice and snow. Water (H2O) forms what are called covalent bonds between the two hydrogen molecules and the oxygen molecule. These chemical bonds are formed by the sharing of electrons between the molecules, but in the case of water, the electrons are not shared equally. The electrons are pulled closer to the nucleus of the oxygen molecule and further away from the hydrogen nucleus, causing the hydrogen to become partly positive, and the overall molecule of water to become polarized, that is having areas that are positively charged and negatively charged in the same molecule. This quality allows what is known as hydrogen bonding to occur. Weak bonds form between one hydrogen of one water molecule and the oxygen of others. This attraction results in a molecular association, which accounts for water’s abnormal properties such as the high boiling point and high melting point, high heat of vaporization and fusion, high surface tension, and the density maximum being as 4 degrees C.

Stellar Dendrite Snowflake Stellar Dendrite Snowflake This hydrogen bonding also accounts for the crystalline structure of ice and snow.

One of my favorite things when I was a child was to go out in the first snowstorm of the year and try to catch snowflakes. I was told that no two snowflakes are exactly alike, and I kept trying to see if it was true. Even with the millions of snowflakes swirling around every winter, it turns out that the old adage is true. These beautiful bits of frozen lace are made unique by the constantly changing conditions of the atmosphere. The rate of growth of the flakes is impacted by the temperature. They begin with just a particle of dust that gathers water. As the water freezes, it forms intricate crystalline structures. Even though each flake is different, they usually take one of seven basic forms.

Rimed Crystal Snowflake Rimed Crystal Snowflake The first is the stellar dendrite, which branches off a basic sixpointed crystal. The branching form occurs in bitter cold conditions. If there is very low humidity, little branching will occur.

Long, thin crystals form with high humidity and warmer temperatures and fall from the sky like needles.

Spatial dendrites are disoriented jumbles of ice. These form when the air is warm and full of water vapor.

Hollow columns or partially hollow columns are commonly seen when the temperature is just below freezing. Bullet rosettes are a number of columns that attach at a single point and often form at high altitudes.

Capped columns resemble squat barbells. These form when the atmospheric conditions are causing a transition from column to plate.

Flat Sectored Plate Snowflake Flat Sectored Plate Snowflake Some snowflakes fall as flat, sectored plates, which form in higher humidity, giving a flat or plate-like appearance.

Crystals specked with rime (frozen water droplets) are another form of snowflake. These form when a stellar dendrite falls through tiny frozen water droplets, which attach to its surface.

Often snowflakes may transition between these different forms, forming “hybrid” flakes, if you will. The type of flake often tells its history, that is, the different atmospheric conditions that it encountered as it fell to earth.

If you get a chance during the next snowfall, take time to look at a few flakes, if you can, with a magnifying glass and see if you can identify some of the forms. You’ve got to do it quickly, because like many beautiful things, they don’t last long.

Trish Martin is a year-around

resident of Mackinac Island, has earned a master’s degree in botany from Central Michigan University, and owns Bogan Lane Inn.

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