University of Tübingen: The inner beauty of the hailstone

Hailstorms recently sparked memories of the devastating storm of 2013. At that time, damage amounting to billions was caused, the damage from the most recent storms is still being recorded. Despite all the annoyance that hailstones mean for people, they also have a previously unknown “inner beauty”: The Tübingen geoscientists Professor Paul Bons and Dr. Catherine Bauer made their crystal structure visible for the first time in a study. They collected grains from the Tübingen storm from 2013 and analyzed them in the laboratory using the most modern methods. In addition to aesthetically pleasing images that have never been created in this way, this also provides information on the structure and possible damage potential of hailstones. The results were recently published in the Journal of Glaciology released.

Paul Bons and Catherine Bauer are both researching on the subject of “ice”, for example in Greenland. In the Tübingen hailstorm in 2013, they reacted immediately and collected hailstones. “We stored these at minus 32 degrees,” explains Bons. “Ice samples should always be stored below minus 28 degrees, otherwise the internal structure can change within weeks.”

For the study he worked with the glaciologist Dr. Maurine Montagnat from the University of Grenoble, France. Her team sectioned the Tübingen hailstones together with others from southwest France and made their inner crystal structure – the texture – visible with an “Automated Ice Texture Analyzer”.

The resulting images show the structure of the crystals in the hailstones in different colors and reveal fascinating patterns and a beauty that is normally hidden from the eye. Each hailstone has an individual structure.

Hailstones arise from raindrops that are transported by updrafts in thunderclouds to great heights of 12,000 meters and more and freeze there. If they fall down, they continue to grow – depending on the temperature and humidity – by freezing new layers of crystals. This procedure can be repeated several times: updrafts carry the grains of ice up into the colder layers, their weight causes them to fall down again. The more violent the thunderstorm, the higher the likelihood that large hailstones will end up on the earth.

Only modern methods made it possible to study the growth stages and complex growth mechanisms of hailstones in much more detail, says Bons. “In this way we can better understand the formation of hailstones and perhaps also better predict the damage they can cause.”

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