The Water Cycle - Water Science for Schools
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The Water Cycle: Sublimation![]() To an adult, this white cloud is just dry ice turning from a solid directly into a gas, but to young Isabelle, sublimation is like magic. Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. For those of us interested in the water cycle, sublimation is most often used to describe the process of snow and ice changing into water vapor in the air without first melting into water. The opposite of sublimation is "deposition", where water vapor changes directly into ice—such a snowflakes and frost. It is not easy to actually see sublimation occuring, at least not with ice. One way to see the results of sublimation is to hang a wet shirt outside on a below-freezing day. Eventually the ice in the shirt will disappear. Actually, the best way to visualize sublimation is to not use water at all, but to use carbon dioxide instead. If you don't know what I mean, then look at this picture of dry ice. "Dry ice" is actually solid, frozen carbon dioxide, which happens to sublimate, or turn to gas, at a chilly -78.5 °C (-109.3°F). The fog you see is actually a mixture of cold carbon dioxide gas and cold, humid air, created as the dry ice "melts" ... oops, I mean sublimates. Find out more about dry ice. From Mt. Everest to the Chinook winds![]() Mt. Everest, losing some snowcover due to a common windstorm. Snow is also constantly lost, invisibly, due to sublimation. Sublimation occurs more readily when certain weather conditions are present, such as low relative humidity and dry winds. Sublimation also occurs more at higher altitudes, where the air pressure is less than at lower altitudes. Energy, such as strong sunlight, is also needed. If I was to pick one place on Earth where sublimation happens a lot, I might choose the south face of Mt. Everest. Low temperatures, strong winds, intense sunlight, very low air pressure—just the recipe for sublimation to occur. Dave Thurlow of the Mount Washington Observatory offers a good explanation of sublimation in The Weather Notebook: "There's more than one way for Mother Nature to get rid of a fresh blanket of snow. The most common way, of course, is by melting-which gives everyone the pleasure of trudging through slush, mud, and water. But in the western U.S., there's a wind called the Chinook, or "snow eater," that vaporizes snow before it even has a chance to melt." "Chinook winds are westerlies from the Pacific whose moisture gets wrung out as it passes over the Rocky Mountains. Once these winds come down from the mountains onto the high plains, they can be quite mild and extremely dry-as warm as 60 or 70 degrees Fahrenheit -- over 15 Celsius -- with a relative humidity of 10% or less. The air is so dry that when it hits a snowpack, the frozen water evaporates, going directly from the ice to vapor and bypassing the liquid phase entirely. This is called sublimation, and it's a common way for snow to disappear in the arid West." Can't sublimate without the heat
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A - Storage in ice and snow B - Precipitation C - Snowmelt runoff to streams D - Infiltration E - Groundwater discharge F - Groundwater storage G - Water storage in oceans H - Evaporation |
I - Condensation J - Water storage in the atmosphere K - Evapotranspiration L - Surface runoff M - Streamflow N - Springs O - Freshwater storage P - Sublimation |
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