Tag Archives: hair-ice

Scientists learn more about hair ice, after 100 years

You may have seen it in forests, and may have dismissed it as an eerie curiosity – a type of ice that looks like white silky hairs, a bit like candy floss. It only grows on rotten branches of trees under very specific conditions, during humid winter nights when the temperature drops just below 0 degrees Celsius. Scientists have believed it is caused by a fungus for over 100 years, but it wasn’t until now that this theory was actually proven.

Hair ice discovered on the forest floor near Brachbach, Germany. Credit: Gisela Preuß.

Alfred Wegener, the famous geophysicist who first proposed the theory of tectonic plates, first discovered white ice in 1918; he and his assistant identified it as a mycelium (the thin threads of mushroom growth), and for almost a century, no one paid any scientific interest to hair ice.

Some 90 years later, retired Swiss professor Gerhart Wagner showed that treating wood with fungicide prevents hair ice from growing, therefore confirming the idea. Now, another Swiss researcher wanted to find out more – and they did.

“When we saw hair ice for the first time on a forest walk, we were surprised by its beauty,” describes study co-author Christian Mätzler, who is from the Institute of Applied Physics at the University of Bern in Switzerland. “Sparked by curiosity, we started investigating this phenomenon, at first using simple tests, such as letting hair ice melt in our hands until it melted completely.”

Screenshot via Youtube.

Mätzler, a physicist, teamed up with a chemist (Diana Hofmann) and a biologist (Gisela Preuß) in Germany. Inspired by earlier work, and by photographs of hair ice sent in from various countries, they performed several tests on the ice to see how it grows and how its structure develops. Preuß studied samples of hair-ice-bearing wood collected in the winters of 2012, 2013 and 2014 in forests near Brachbach in western Germany and found several different fungus species.

“One of them, Exidiopsis effusa, colonised all of our hair-ice-producing wood, and in more than half of the samples, it was the only species present,” she says.

Hair ice in forest near Moosseedorf, Switzerland. Credit: Christian Mätzler.

Mätzler’s contribution was understanding the physics of the ice. His work confirmed guesses made by previous researchers, showing that the mechanism that creates the ice filaments at the wood surface is ice segregation.

“The process of Ice Segregation takes place in a porous medium when supercooled water moves to the presence of ice and adds to the ice through freezing. In this case the ice grows away from the ice/water interface,” writes Dr. James R. Carter a professor at the Illinois State University who was not involved in the study.

Interestingly, the fungus formation doesn’t affect the quantity of ice in any way – only its structure.

“The same amount of ice is produced on wood with or without fungal activity, but without this activity the ice forms a crust-like structure. The action of the fungus is to enable the ice to form thin hairs – with a diameter of about 0.01 mm – and to keep this shape over many hours at temperatures close to 0°C. Our hypothesis includes that the hairs are stabilised by a recrystallisation inhibitor that is provided by the fungus.”

Image via Btween Blinks

Hoffman then studied the hair ice itself, chemically. She found that the ice contained fragments of complex organic molecules – lignin and tannin – involved in fungus metabolism, further confirming the fungal effect.

It took over 100 years to confirm Wegener’s theories about hair ice, a fairly common phenomenon; this can makes me wonder, how many other common things are still waiting to be understood in our forests.

Journal Reference.


Nature’s toupee: fungus weaves astonishing hair-ice

For over a century since it was described, a peculiar type of ice known as hair-ice or ice wool has been puzzling scientists. Now, the mystery seems to have been solved. The uncanny fine hairs of ice, which are only 0.02 mm thick and can grow to 20 cm in length, are actually caused by a fungus.


Image: Christian Mätzler

If this is the first time you’ve heard of hair-ice, you’re not alone. It’s quite a rare event. It only grows in latitudes between 45 and 55 degrees N in the forests where there are particular conditions for humidity. Typically, you’ll find these growing during the chilly mornings right before the sun rises and melts them, and only on  the surface of the unfrozen wood body of certain moist and rotten branches of broad-leaf trees.


In 1918, a German scientists called Alfred Wegener  first proposed that these amazing hair-ice crystals which follow a surprisingly orderly structure are caused by a fungus. Wegener and his assistants noticed a whitish cobwebby coating on the surface of the hair-ice bearing rotten wood. Upon closer examination, the coating was found to be a mycelium  – a mass from which fungus grows.

Many years later, retired Swiss professor Gerhart Wagner proved there’s a relation between the fungus and the beautiful cotton-ice that grows trees. Him and colleagues treated samples of hair-ice bearing wood with fungicides or dunked them in hot water and found the ice crystal formation in thin hairs was suppressed. After carefully analyzing the wood samples with microscopic techniques, Wagner and colleagues discovered eleven different species of fungus. Only one fungus was found present in all samples, a species called  Exidiopsis effusa

hair-ice fungus

Image: Gisela Preuß

Christian Mätzler from the Institute of Applied Physics at the University of Bern in Switzerland, a close collaborator of Wagner, found the ice is formed by a process known as ice segregation.

“Liquid water near the branch surface freezes in contact with the cold air, creating an ice front and sandwiching a thin water film between this ice and the wood pores. Suction resulting from repelling intermolecular forces acting at this wood–water–ice sandwich then gets the water inside the wood pores to move towards the ice front, where it freezes and adds to the existing ice,” Mätzler explains.

So, basically the shape of the ice is determined by the tiny pores found in the rotten wood. It’s like the ice gets extruded, much like a 3D-printer jets plastic through its nozzle. But where does the fungus come in all this? Chemical analysis suggests the samples contain  lignin and tannin, which are metabolic products of fungal activity. It may be very well that these components prevent large ice crystals from forming, retaining the clear and beautiful hair-like appearance. The findings appeared in the journal Biogeosciences.