Hair? Ice? Fungus?

Photographs and words Nick Sidle

Photograph – Battan Forest, Glen Convinth, Inverness-shire, Highland Scotland

The answer is actually all three. This rare phenomenon is called hair ice and is made up of tiny filaments of ice crystals formed on and exuding from dead wood when the conditions are right, it is the infrequent occurrence of the perfect conditions that means it is so rarely seen. It arises from the pores in the wood structure where the bark has been lost.

Photograph – Hair Ice, Battan Forest, Glen Convinth, Inverness-shire, Highland Scotland

What is required is a very cold temperature below freezing, for the dead wood to be saturated with water and very wet and for the right humidity in the surrounding air which must be high. After that, this particular type of frost can form as hairs about 0.01mm in diameter so it is no surprise that if you touch it, it melts. Now comes the fungal bit. For hair ice to form, what is also required is the presence of a fungus, Exidiopsis effusa, in the wood – an association reported by a team of scientists from Switzerland and Germany and reported in the journal Biogeosciences.

Evidence for biological shaping of hair ice:

https://www.biogeosciences.net/12/4261/2015

Photograph – Hair Ice, Battan Forest, Glen Convinth, Inverness-shire, Highland Scotland

Hair ice was first recognised and studied in 1918 by Alfred Wegener, perhaps better known for his work on the slightly larger in scale question of tectonic plates. He suggested an association with fungus but it is only the recent work that has finally revealed what that is. In the absence of the fungus, ice forms on the surface of the wood as an encrusting layer, only if the fungus is present then the hairs form and, subject to the temperature staying below freezing, grow. The researchers hypothesis is that the hair ice structures are stabilised by a recrystallization inhibitor that comes from the Exidiopsis effusa. The team showed the presence of complex organic compounds, lignin and tannin, in the ice and identify these as the substances preventing the formation of larger ice crystals on the surface of the wood. Lignin and tannin are metabolic products of fungal activity and Exidiopsis effusa appears to have been the organism to provide all the right conditions.

Photograph – Hair Ice, Battan Forest, Glen Convinth, Inverness-shire, Highland Scotland

For someone thinking as a scientist, this sort of discovery makes a beautiful natural phenomenon, even more a wonder of the forests. If for you complex organic compounds get in the way of appreciating a fleeting, unusual and exquisite event in the wild, then there is still the alternative name of ‘Snow Fairy’.