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| Sunday, 16 January 2005 |
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Junior Observer |  |
| News Business Features Editorial
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White as snow When we hear the word 'winter', the first thing that comes to mind is snow. Sri Lanka does not experience the fall of snow, except for very rare occasions of slight frost in Nuwara Eliya. However, thousands of people gathering in Colombo last month to experience an artificial snowfall is the best example that we all like to be a part of this wonderful experience.
In simple words, snow is frozen water vapour in the atmosphere that falls in light white flakes. The seasonal snow cover, the largest component of the cryosphere (area covered with snow), covers up to 33 per cent of the Earth's total land surface. About 98 per cent of the total seasonal snow cover is seen in the Northern Hemisphere. Although snowdrifts and avalanches (a mass of snow and ice falling rapidly down a mountainside) often pose hazards to humans, snow also provides much of the world's water. Snow is a very versatile material. Sometimes it can be very hard, but it can also be very gentle. Temperature has a great effect on the properties of snow. When temperature is over zero degrees Celsius, snow is very wet and heavy, but it has excellent adhesive force. When temperature is below zero degrees, snow is very light and fine, all moisture has frozen and the snow is almost lighter than air. It is also very dry and it's impossible to form any constructions out of such snow with traditional methods. Freshly fallen snow maybe the finest material in the world, but it easily becomes hard and thick. If pressure is directed on snow, it becomes excellent building material. Compressed snow can be compared to light concrete, while ice can be compared to concrete. Snow is still weaker than ice, but snow has better workability and insulates heat better. Have you ever wondered why snow is white? Visible sunlight is white and most natural materials absorb some sunlight which gives them their colour. Snow, however, reflects most of the sunlight. The complex structure of snow crystals results in countless tiny surfaces from which visible light is efficiently reflected. What little sunlight is absorbed by snow is absorbed uniformly over the wavelengths of visible light, thus giving snow its white appearance. Most heavy snowfalls occur with relatively warm air temperatures near the ground - typically 15 degrees Fahrenheit or warmer, since air can hold more water vapour at warmer temperatures. But, it can snow even at incredibly cold temperatures as long as there is some source of moisture and some way to lift or cool the air. The water content of snow is more variable than most people realize. While most snow that fall at temperatures close to 32 degrees Fahrenheit, and snow accompanied by strong winds contain approximately one inch of water per ten inches of snowfall, the ratio is not always accurate. Ten inches of fresh snow can contain as little as 0.10 inches or upto four inches of water, depending on the crystal structure, wind speed, temperature, and other factors. The majority of snow which falls in the U.S. has a water-to-snow ratio of between 0.04 and 0.10 inches. And did you know that clean snow is edible? Snow in urban areas may contain pollutants that one should not eat, but they would probably be in such low concentrations that it will not matter. Still, eating snow should be restricted to "wilderness" areas. Sometimes snow contains algae which gives it a red colour. This snow can be eaten and some say it actually tastes good. Although it is believed that snow is colder in deeper spots, studies have proved that this is not correct. The temperature at the surface of the snow is controlled by the 'air temperature'. The colder the air above, the colder the snow layers near the surface (within the top 12 to 18 inches). The snow near the ground remains deeper. Snowcap however is warmer as it is closer to the warm ground. The ground is warm because the heat stored in the ground over the summer is slow to leave the ground since snow is a good "insulator", just like the insulation in the ceiling of your house. It slows the flow of heat from the warm ground to the cold air above. Ice crystals have six points. One snowflake can consist of multiple crystals. There are gaps between the points of a crystal that are empty, except for air. When snow falls to the ground, air is trapped inside that layer of snow. If you have had a chance to step on snow, you would have probably noticed that it gets compressed. The air gets pushed out of the snow. This process also makes a sound created by the breaking of ice crystals. Try it with ice cubes. They make a crunching sound when broken. *** Glaciers
A body of ice that covers a large area of land and flows outward in all directions is called an ice cap or ice sheet. Ice caps form in high mountain summits and plateau regions. Two ice sheets exist on Earth now, one in Greenland and one in Antarctica. All continents except Australia bear ice in the form of mountain glaciers, ice sheets, or ice caps. Today, glaciers and ice sheets store about 75 per cent of the world's freshwater. |
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Glaciers and ice sheets cover about 10 per cent of the Earth's land
area. Glaciers, which are large, thickened masses of ice, accumulate from
snowfalls over long periods of time. When these ice masses reach a
critical thickness, they begin to move, or flow.
