How is it that snowflakes are different

Why every snowflake is unique

How is snow made?

It starts with small, supercooled drops of water that freeze to ice crystals in the clouds. Water vapor is deposited on it and the crystals begin to grow. Snow crystals can look like stars or needles under the microscope, but they always have a hexagonal, i.e. hexagonal, crystal structure. When ice crystals come into contact, they combine. That means "sintering".

How big is an ice crystal?

An average small crystal is so tiny that it can hardly be seen with the naked eye. On average, however, it already contains a trillion water molecules (a 1 with 18 zeros). Each crystal grows differently depending on the humidity and temperature and is therefore unique. Snowflakes are created from several crystals. An ice crystal ball with a diameter of one millimeter weighs an average of four milligrams.

How heavy is snow

One cubic meter of fresh snow weighs around 100 kilograms. "New snow consists of 90 percent air," says physicist Henning Löwe from the Swiss Institute for Snow and Avalanche Research (SLF) in Davos. For comparison: one cubic meter of water weighs ten times as much. "At the end of the season, one cubic meter of snow can weigh 400 to 500 kilograms, on the slopes or in an avalanche deposit even 600 kilograms."

What happens in a pile of snow?

The flakes have a complex shape. When they collapse, they don't condense immediately. That only happens over time. In a blanket of snow, some crystals absorb water vapor, others give it off. The flakes and the ice crystals grow together. A porous structure is created, similar to a sponge that is compressed over time.

Why is snow white?

The individual flakes in the snow scatter the incident light on their surfaces like tens of tiny mirrors standing in different directions. The resulting superimposition of all colors radiated by the sun perceives the eye as white. This effect of millions of light refraction is also effective in the bubble bath. According to the SLF Institute, no natural surface reflects more visible light than freshly fallen snow. "If you peel off a bit of a pure, transparent ice cube, it will also appear in white color," says Löwe. Older snow appears darker. On the one hand, this is due to dust and other deposits. But when the ice crystals grow together and get bigger, the light inside is also refracted differently.

Why is there silence in a snow-covered landscape?

Because 90 percent of fresh snow consists of air, which fills its labyrinthine pore space. “It's a good sound absorber, it suppresses ambient noise,” says Löwe. The reason that the snow crunches underfoot is because the ice crystals break.

How is artificial snow made?

Snow cannons blow small water droplets into the cold air, which ideally freeze on the way to the ground. But natural snowflakes are created from water vapor. The snow crystal in artificial snow has the shape of a drop of water or a fragment of it. The proportion of air in the fallen snow is much smaller than in real snow made from water vapor.

Can you also create real snow artificially?

Yes, with a large snow machine in the laboratory, but that is very time-consuming.

How is the snow researched in the laboratory?

The snow comes into a snow breeder, a kind of large can that has different temperatures above and below. In a computer tomograph, the scientists then use X-ray light to observe how the snow crystals inside are changing. Computer simulations for predictions about changes in the snow cover are developed from the findings. This is interesting, for example, for determining the amount of snow, according to Löwe. So far, a satellite can only determine how large the snow-covered area on earth is. Microwave, radar or emission measurements from satellites could record more reliably how much snow there is globally if the microstructure of snow is better researched.

red, science.ORF.at/Agenturen

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