Hair ice is a rare type of ice formation where the presence of a particular fungus in rotting wood produces thin strands of ice which resemble hair or candy floss.
One of the first records of the phenomenon was made by Alfred Wegener (the discoverer of continental drift) in 1918. He observed a strange ice forming only on wet dead wood and proposed a theory that a specific fungi must be the catalyst for the smooth, silky hairs of ice.
How does hair ice form?
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.
In 2015 the scientists Hofmann, Mätzler and Preuß determined the exact cause of the hair ice phenomenon, linking its formation to the presence of a specific fungus called Exidiopsis effusa.
They discovered that the presence of the fungus led to a process called 'ice segregation'. When water present in the wood freezes it creates a barrier that traps liquid between the ice and the pores of the wood. This creates 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.
It is believed that an inhibitor present in the fungus allows the strands of ice to stabilise allowing the formation of the beautiful phenomena and allows the hair ice to keep its shape often for several hours.
Video: Hair ice formation timelapse
The video below shows the formation of hair ice recorded by timelapse photography: