We walked past the first branch covered in pure white snow with barely a glance. After a few moments, a voice inside my head gave me a nudge, remarking ‘but it hasn’t actually snowed.’ When we passed a few more branches looking like they were doing auditions for the cover of Christmas cards, we decided they required closer inspection. It turned out the white, crisp substance layered on top of each branch wasn’t snow at all, but a rare phenomenon called hair ice.
The Met Office describes hair ice as being ‘a rare type of ice formation where the presence of a particular fungus in rotting wood produces thin strands of ice that resemble hair or candy floss.’
From a distance it easily passes as snow. It’s only when you get up close you can see the thin strands, like a snow queen’s vermicelli. It is quite beautiful, a result of nature waking up and thinking, you know what, I’m feeling artistic today. The reason it is considered rare is that hair ice can only occur in certain conditions within a limited geographical band (between 45° and 55°N latitudes, which takes in England and a part of Scotland), when the air is moist, and temperatures are only just below 0°C. It also requires a quite specific host, the rotting branches from broadleaf trees such as ash, oak, or silver birch infected with the fungus exidiopsis effusa. This set of circumstances can result in ice forming in thin strands, like frosted hairs. Although sightings were recorded a hundred years ago, it was only officially identified by scientists in 2015.
As well as being rare, hair ice is a transient treat, lasting only a few hours. We felt privileged to have seen five or six exquisite examples of this beautiful anomaly during a walk around Clatworthy Reservoir in Somerset in December, especially as snow did fall the following day. Even if some branches with hair ice survived, they would be invisible, totally camouflaged.