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This article is about water ice. Unsourced material may be challenged and removed. Frozen water in the form of an ordinary household ice cube. The white zone in the center is the result of tiny air bubbles.
An unusual property of ice frozen at atmospheric pressure is that the solid is approximately 8. Liquid water is densest, essentially 1. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. Density of ice increases slightly with decreasing temperature and has a value of 0. It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes.
This creates a sheltered environment for bacterial and algal colonies. Compared with water, this absorption is shifted toward slightly lower energies. Thus, ice appears blue, with a slightly greener tint than liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice. Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. Ice was originally thought to be slippery due to the pressure of an object coming into contact with the ice, melting a thin layer of the ice and allowing the object to glide across the surface.
For example, the blade of an ice skate, upon exerting pressure on the ice, would melt a thin layer, providing lubrication between the ice and the blade. This explanation, called “pressure melting”, originated in the 19th century. C, which is often skated upon. These molecules remain in a semi-liquid state, providing lubrication regardless of pressure against the ice exerted by any object. In the 20th century, a further explanation, called “friction heating”, was proposed, whereby friction of the material is the cause of the ice layer melting. However, this theory does not sufficiently explain why ice is slippery when standing still even at below-zero temperatures. More recently, a comprehensive theory of ice friction, which takes into account all the above-mentioned friction mechanisms, has been presented.
This model allows quantitative estimation of the friction coefficient of ice against various materials as a function of temperature and sliding speed. In typical conditions related to winter sports and tires of a vehicle on ice, melting of a thin ice layer due to the frictional heating is the primary reason for the slipperiness. Ice is an important component of the global climate, particularly in regard to the water cycle. Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle.
The result is a stratified ice deposit, often several meters thick. Ice which forms on moving water tends to be less uniform and stable than ice which forms on calm water. Ice jams can cause flooding, damage structures in or near the river, and damage vessels on the river. Heavy ice flows in rivers can also damage vessels and require the use of an icebreaker to keep navigation possible. Ice forms on calm water from the shores, a thin layer spreading across the surface, and then downward. Ice on lakes is generally four types: Primary, secondary, superimposed and agglomerate. Secondary ice forms below the primary ice in a direction parallel to the direction of the heat flow.
Superimposed ice forms on top of the ice surface from rain or water which seeps up through cracks in the ice which often settles when loaded with snow. Rime is a type of ice formed on cold objects when drops of water crystallize on them. Ice pellets are usually smaller than hailstones. This causes the partial or complete melting of any snowflakes falling through the warm layer.
As they fall back into the sub-freezing layer closer to the surface, they re-freeze into ice pellets. However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze, and freezing rain will be the result at the surface. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. GR is used to indicate larger hail, of a diameter of at least 6. The hailstone then may undergo ‘wet growth’, where the liquid outer shell collects other smaller hailstones. The hailstone gains an ice layer and grows increasingly larger with each ascent.
Once a hailstone becomes too heavy to be supported by the storm’s updraft, it falls from the cloud. Hail-producing clouds are often identifiable by their green coloration. Hail in the tropics occurs mainly at higher elevations. The droplet then grows by condensation of water vapor onto the ice surfaces.
The ordering of the molecules in the solid breaks down to a less ordered state and the solid melts to become a liquid. The velocity of the melting process depends on the efficiency of the energy exchange process. In salty ambient conditions, dissolution rather than melting often causes the ablation of ice. Arctic Ocean is generally below the melting point of ablating sea ice.