Hair ice

Hair ice, also known as ice wool or frost beard, is a type of ice that forms on dead wood and takes the shape of fine, silky hair.^[1] It is somewhat uncommon, and has been reported mostly at latitudes between 45 and 55 °N in broadleaf forests.^[1]^[2] The meteorologist (and discoverer of continental drift) Alfred Wegener described hair ice on wet dead wood in 1918,^[3] assuming some specific fungi as the catalyst, a theory mostly confirmed by Gerhart Wagner and Christian Mätzler in 2005.^[4]^[5]^[6] In 2015, the fungus Exidiopsis effusa was identified as key to the formation of hair ice.^[1]

Formation

Hair ice forms on moist, rotting wood from broadleaf trees when temperatures are slightly under 0 °C (32 °F) and the air is humid.^[1] The hairs appear to root at the mouth of wood rays (never on the bark), and their thickness is similar to the diameter of the wood ray channels.^[1] A piece of wood that produces hair ice once may continue to produce it over several years.^[1]

Each of the smooth, silky hairs has a diameter of about 0.02 mm (0.0008 in) and a length of up to 20 cm (8 in).^[1] The hairs are brittle, but take the shape of curls and waves.^[1] They can maintain their shape for hours and sometimes days.^[1] This long lifetime indicates that something is preventing the small ice crystals from recrystallizing into larger ones, since recrystallization normally occurs very quickly at temperatures near 0 °C (32 °F).^[1]

In 2015, German and Swiss scientists identified the fungus Exidiopsis effusa as key to the formation of hair ice.^[1] The fungus was found on every hair ice sample examined by the researchers, and disabling the fungus with fungicide or hot water prevented hair ice formation.^[1] The fungus shapes the ice into fine hairs through an uncertain mechanism and likely stabilizes it by providing a recrystallization inhibitor similar to antifreeze proteins.^[1]^[2]

References

^ a b c d e f g h i j k l m Hofmann D, Preuss G, Mätzler C (2015). "Evidence for biological shaping of hair ice" (PDF). Biogeosciences. 12 (14): 4261–4273. Bibcode:2015BGeo...12.4261H. doi:10.5194/bg-12-4261-2015.
^ a b European Geosciences Union (22 July 2015). "Press Release: Fungus shapes hair ice – Researchers identify fungus responsible for peculiar ice filaments that grow on dead wood". Retrieved 24 July 2015.
^ Alfred Wegener: Haareis auf morschem Holz. Die Naturwissenschaften 6/1, 1918. S. 598–601.
^ Gerhart Wagner: Haareis – eine seltene winterliche Naturerscheinung. Was haben Pilze damit zu tun? SZP/BSM 2005.
^ Gerhart Wagner, Christian Mätzler: Haareis auf morschem Laubholz als biophysikalisches Phänomen. Archived 2016-03-04 at the Wayback Machine Forschungsbericht Nr. 2008-05-MW. Universität Bern. 2008. (PDF-Download Archived 2016-03-04 at the Wayback Machine)
^ Gerhart Wagner, Christian Mätzler: Haareis - Ein seltenes biophysikalisches Phänomen im Winter. Naturwissenschaftliche Rundschau 62(3), S. 117–123 (2009), ISSN 0028-1050