Ice is solidified water and appears in a wide variety of forms in nature. Ice can be a nuisance, especially if we have to scrape it off the car windscreen before we can drive. But it can also look enchanting, especially when it appears in the form of ice flowers. The forms that ice can take are many and diverse, as are the benefits and potential hazards associated with it.
The different forms of ice include:
So, ice comes in many different forms and can transform easily from one into another. It can be short-lived, or it can last a long time.
In normal circumstances, the freezing point of water is zero degrees Celsius. But for ice crystals to form, ice nucleating particles are needed (e.g. dust particles). The more similar the surface structure of a material is to ice, the more suitable it is as a nucleating particle.
Highly purified water can be cooled to below -30 degrees in a laboratory before it freezes. When liquid water has a temperature of below zero degrees, this is known as “supercooled water”. The freezing point of water can be lowered by adding salt (or sugar), a fact that is exploited by the winter road maintenance services to prevent or delay ice formation on roads.
In summary, ice can form in the presence of sufficient moisture, ice nucleating particles and sub-zero temperatures. Because the density of ice is lower than that of liquid water (known as the water density anomaly), ice floats on the surface of water. Only about 10% of the ice volume protrudes from the water, leaving the remaining 90% of the ice volume below the water’s surface.
Below, the formation processes of the most common ice forms are briefly described.
Ice can serve a variety of purposes, such as freezing food, protecting plants against frost (in german) in agriculture, making winter sports possible, or facilitating transportation in winter.
But ice can also be a nuisance, or even hazardous:
Last but not least, ice can enchant us with delicate, sometimes fleeting phenomena such as hair ice and frost, or as man-made ice sculptures.