Two conditions are necessary for the formation of ice: the presence of water and temperatures below freezing. Ice in the atmosphere and on the ground can assume various forms, depending on the conditions under which water is converted to its solid state. Ice that forms in the atmosphere can fall to the ground as snow, sleet, or hail. Snow is an assemblage of ice pellets. Hail consists of rounded or jagged lumps of ice, often in layers like the internal structure of an onion. Ice also forms directly on the ground or on bodies of water, it may not form until late winter because there must be several months of low temperatures to chill such large amounts of water.
On puddles and small ponds, ice first freezes in a thin layer with definite crystal structure that becomes less apparent as the ice thickens. On lakes large enough to have waves, such as the Great Lakes, the first ice to form is a thin surface layer of slush, sometimes called grease ice, which eventually grows into small floes may freeze together into a fairly solid sheet of pack ice. Pack ice may cover the entire lake or be restricted to areas near the shore.
Because water expands when it freezes, ice is less dense than liquid water and therefore floats rather than sinks in water. As ice floats on the surface of a lake, ocean, or river, it acts as an insulator and is thus important in maintaining the balance of the ecosystem. Without the insulating effect of floating ice sheets, surface water would lose heat more rapidly, and large bodies of water such as the Arctic Ocean and Hudson Bay might freeze up completely.
Questions:
1. What condition is necessary for water in the atmosphere to change to its solid state?
A. A solid cloud cover that absorbs the sun's heat.
B. A weather forecast for snow, sleet, or hail
C. A position directly above a large body of water
D. A temperature below water's freezing point
2. Ice that forms in the atmosphere in the form of layered lumps is known as
A. snow
B. pack ice
C. hail
D. grease ice
3. Why does ice form later on very large bodies of water?
A Most large bodies of water are located at low elevations or low latitudes.
B. It takes several months of cold temperatures to cool a large body of water.
C. Large bodies of water are fed by underground springs of warmer water.
D. The waves on large bodies of water prevent the water from freezing quickly.
4. The word it in paragraph 3 refers to
A. water
B. ice
C. surface
D. river
5. Which of the following is an effect of the density of ice?
A. Ice that forms on large lakes has a greasy consistency.
B. Each ice crystal is unique, but all are six-sided structures.
C. Pack ice is restricted to areas near the shore of a lake.
D. Floating ice sheets prevent bodies of water from losing heat.
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