Why is it possible for the surface of a pond to freeze even though the water underneath is fluid?

Answer 1

Because water is not the same as other liquids. Water starts to expand as it approaches freezing so it floats when ice forms. Other liquids don't do this strange trick.

Answer 2

Ice floats.

Water at the deepest part of the pond will be the coldest. As it freezes, it becomes less dense and rises to the surface as ice crystals. After the entire depth is cold enough as to not warm the rising ice crystals to the melting point during thier ascent, they will rest on the surface. Once ice crystals are established at the surface, below freezing air temperatures will allow the ice crystals to grow into a sheet of ice.

The thickness of the ice will depend on the enviroment. The longer the freeze lasts, and colder the temperature, will determine how thick the ice can get. (Water currents also come into effect). If it is cold enough, long enough, a pond can freeze solid through it's entire depth.

Answer 3

When the air is very cold and the water is losing heat through radiation and a little convection at the surface, the surface water becomes cooler and since the water at 0 C is lighter than the water at 4C, ice can form at the surface and water can remain below.

Answer 4

the actual answer is a little more complicated. the more pressure water is under, the lower the freezing point becomes. the deeper the water, the colder the temp. has to be to freeze the bottom. therefore, the top frezes first, with normal pressure. thats why you dont walk on a pond at 30 degrees...you wait till its like 10 degrees for a week before walking on ice.

this is also why ocean water can be in liquid form but measured at below 32 degrees.

Answer 5

because the water below is insulated from the cold air above it. The ground experiences the same thing, where only a foot or so freezes.

Answer 6

Because it is directly exposed to the below freezing air, and loses enough of it's own heat to, in turn, freeze.

The following is an excerpt from Wikipedia. It doesn't have much to do with the freezing of water, but contains a range of facts about water on Earth. I just found it interesting, and thought I'd share...

Water on Earth
The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.

Earth's approximate water volume (the total water supply of the world) is 1 360 000 000 km3 (326 000 000 mi3). Of this volume:

1 320 000 000 km3 (316 900 000 mi3 or 97.2%) is in the oceans.
25 000 000 km3 (6 000 000 mi3 or 1.8%) is in glaciers, ice caps and ice sheets.
13 000 000 km3 (3,000,000 mi3 or 0.9%) is groundwater.
250 000 km3 (60,000 mi3 or 0.02%) is fresh water in lakes, inland seas, and rivers.
13 000 km3 (3,100 mi3 or 0.001%) is atmospheric water vapor at any given time.
Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is sea water. Water is also present in the atmosphere in solid, liquid, and vapor phases. It also exists as groundwater in aquifers.

The boiling point of water is directly related to the barometric pressure. For example, on the top of Mt. Everest water boils at about 68 degrees Celsius, compared to 100 degrees at sea level. Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.

Answer 7

Yesss

Answer 8

the air is colder than the eath, the ice also forms an insulation layer (as strange as it sounds) between the air and the water. reducing how much heat escapes from under the ice.