Hair Ice and Fungi's Involvement
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Hair Ice was first observed by continental drift discoverer, Alfred Wegener in 1918. A rare type of ice formation, Hair Ice grows exclusively on dead wood and he theorised it was due to some sort of fungal growth. Almost 100 years later, science has the answers.
Wegner theorised it was due to a fungi but it wasn't until 2015 where German and Swiss scientists Hofmann, Mätzler and Preuß found the cause of hair ice, linking its formation to the presence of a specific fungus called Exidiopsis effusa.
Exidiopsis effusa is part of the Auriculariaceae family which contain 7 genera and over 100 species which usually live on dead, fallen or rotting woods.
In the study, Preuß examined samples of dead wood that had previously grown hair ice from the winters of 2012, 2013 and 2014 in forests near Brachbach in western Germany. Preuß placed these under a microscope and found 11 different species of fungi. When the Hair Ice was investigated microscopically Preuß found Exidiopsis effusa on every hair ice sample examined by her and she was able to disable the fungus with fungicide and prevent hair ice forming.
The presence of the Exidiopsis effusa led to a process called 'ice segregation'. Which is where water in the wood begins to freeze and it creates a barrier that traps liquid between the ice and the pores of the wood.
This created a suction force which pushes water out of the pores to the edge of the ice surface where it freezes and extends outwards. As this repeats it pushes a thin 'hair' of ice out of the wood which is around 0.01 mm in diameter, an inhibitor similar to antifreeze proteins present in the fungus allows the strands of ice to stabilise over several hours sometimes days.
The researchers also found that the root of the hair ice, called a crystallization nucleus, is likely composed of lignin and tannin. Lignin is found in vascular plants like mosses and conifers and help give wood its hardness and resistance to rotting. Tannin also occurs widely in vascular plants and protects plants from herbivores who dislike its bitter taste.
According to The Met Office, "The conditions required for the formation of hair ice are extremely specific, hence the relative scarcity of sightings. To form, moist rotting wood from a broadleaf tree is required with the presence of moist air and a temperature slightly below 0 °C. It is generally confined to latitudes between 45°N and 55°N."
"The same amount of ice is produced on wood with or without fungal activity, but without this activity, the ice forms a crustlike structure," Christian Mätzler.
It's worth noting if you go out looking for it in the right conditions that Hair Ice is very rare and it will grow mostly at night and melt in the morning sun. It grows only at the mouth of wood rays and never on the bark and their thickness is similar to the diameter of the wood ray channels. A piece of wood that produces hair ice once may continue to produce it over several years so if you do see some it's worth revisiting it the next year.
For those interested in some hardcore science Biogeoscience have the original publication by the scientists on: Evidence for biological shaping of hair ice