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Icicle

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An icicle is a spike of ice formed when water falls from an object and freezes. These frozen structures are common in cold environments. They often appear when melting snow or ice drips from a surface. This process can happen even during bright, sunny weather. If the air temperature remains below freezing, the water refreezes as it drips. Icicles can grow into many different shapes. Their form depends on the surface they hang from. A smooth surface might create a straight icicle. An irregular surface might create a more complex shape.

Ice formations 2
Ice formations 2

The growth of an icicle is a specific physical process. It grows by forming an ice tube around a pendant drop of water. The wall of this ice tube is very thin. Because the wall is so thin, the interior of a growing icicle remains liquid water. The rate at which an icicle grows in length and width is a complicated function. It depends on air temperature, wind speed, and water flux. Water flux is the amount of water flowing into the icicle. In ideal conditions, the length can increase by more than 1 centimeter per minute.

There are several distinct ways that icicles form in nature. One way occurs during ice storms. In these storms, rain falls through air that is slightly below freezing. This rain accumulates as many small icicles on twigs, leaves, or wires. Another way is through water seeping from vertical surfaces. This often happens at road cuts or on cliffs. If the conditions are right, these can form frozen waterfalls. These large structures are often used by ice climbers.

Icicles can also be found in unusual environments. When they form inside caves, they are known as ice stalactites. They can even form in the ocean within salty water called brine. As brine sinks from sea ice, it can create structures called brinicles. These are sometimes called "ice fingers of death." BBC film crews observed these near Mount Erebus in Antarctica. They filmed this phenomenon for the show Frozen Planet in 2011. These brinicles are powerful enough to kill sea urchins and starfish.

While they are beautiful, icicles pose significant personal and structural dangers. Falling icicles can cause injury to people or damage objects below. They can also be very heavy. If many icicles form on a wire, beam, or pole, the weight is immense. This weight can damage the structural integrity of the object. It can even cause the object to break. On roofs, icicles are often linked to ice dams. These dams allow water to penetrate below the shingles of a building.

History and research have documented the dangers of these ice spikes. A story from 1776 recounts an English youth killed by a falling icicle. Modern science has also studied their impact on the human body. A study from 2022 showed that icicles can penetrate most of the human body. With enough depth, they can reach vital organs. The only major exception noted was the chest region. Large icicles on cliffs near highways can also damage moving motor vehicles.

Large-scale events show how dangerous icicles can be in populated areas. In 2010, Saint Petersburg, Russia, experienced a major incident. Five people were killed and 150 people were injured by icicles there. This happened after heavy snow caused apartment block roofs to collapse. The ice and snow also caused water damage to private homes. This damage even affected the National Library of Russia. These events show how ice can impact entire cities and important buildings.

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File:Ice formations 2.jpg
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