A team of Swiss and German scientists have discovered that hair ice, a phenomenon in which oddly-textured ice is formed on rotten tree branches and dead wood, is caused by a species of fungus known as Exidiopsis effusa.

In a study featured in the European Geosciences Union's open-access journal Biogeosciences, researchers from Switzerland's University of Bern and Germany's Wiedtal-Gymnasium found that the fungus was present in all of the wood they observed that exhibited hair ice.

Christian Mätzler, a researcher at Bern's Institute of Applied Physics, said that they took their inspiration in studying Exidiopsis effuse after seeing hair ice during a walk in the forest. He explained that they began their research by conducting simple experiments on the crystalline specimen, such as observing the hair ice melt in their hands completely.

Discovery of Hair Ice

The hair ice phenomenon was first observed in 1918 by Alfred Wegene, the scientists who provided the original study on plate tectonics. Wegene discovered hair ice on a piece of wood that contained fungus mycelium.

Mätzler and his colleagues Diana Hofmann and Gisela Preuß believe that this strange phenomenon could be linked to ice and the growth of the fungus on the dead wood.

Retired Swiss educator Gerhart Wagner provided further research on hair ice some 90 years later after Wegene's findings. He found that when the wood with hair ice is treated with fungicide, the chemical is able to suppress the development of the strange crystalline substance.

Wagner's findings led the researchers to examine various species of fungi in samples of wood gathered from forests in the West German town of Brachbach during the winters of 2012, 2013 and 2014. They also studied specimens of hair ice taken from a forest near Moosseedorf in Switzerland.

How the Hair Ice are Formed

In their subsequent tests, Mätzler and his team discovered that the water present in the wood froze, producing an ice front that trapped the liquid between the film of ice and the pores of the wood. Repelling intermolecular forces then created suction that pushed the water into the pores, where it eventually froze and added onto the existing ice. The development of the ice is dependent on the wood rays on the mouth of the ice formations.

While ice can still form even without the presence of fungal activity, the findings showed that the resulting ice formations appear more similar to ice crusts rather than the hair-like structures seen when the Exidiopsis effusa is present.

The fungus helps produce the characteristic ice hairs, with an average diameter of around 0.01 millimeters for each strand. It also allows them to maintain their frozen form for hours at zero-degree temperatures. Mätzler said that they believe the hair ice is stabilized by an inhibitor present in the fungus, allowing it to re-crystallize.

The researchers also found evidence of the organic compounds tannin and lignin, both of which are known to be the metabolic products of activity in fungi.

Study co-author Hofmann said that these two factors could be the ones that prevent the formation of larger crystalline structures on the surface of the wood.

The findings of the University of Bern-led study are published in the journal Biogeosciences.