What is hair ice? The mysterious weather phenomenon appearing on trees

Hundreds of individual strands of frozen water are held together in what looks like candy floss

Hundreds of individual strands of frozen water are held together in what looks like candy floss (EPA)

An unusual growth resembling candy floss has been forming on tree branches in Northern Irish woodland. 

The strange sight, spotted in the counties Fermanagh and Tyrone, is a rare phenomenon called hair ice, in which hundreds of individual strands of frozen water are held together in what looks like a soft white wig.

The formation occurs in the presence of a particular fungus in rotting wood, Exidiopsis effusa, but the conditions required are extremely specific.

Moist wood from a broadleaf tree is needed, as well as humid air and temperatures just below freezing.

The science behind the phenomena was disputed for a long time, but in 2015, Swiss and German researchers Diana Hofmann, Christian Mätzler and Gisela Preuß arrived at an answer. They found that the presence of the fungus allowed the thin ‘hairs’ of ice being pushed out of the wood to stabilise, keeping its wonderful form for several hours.

“The action of the fungus is to enable the ice to form thin hairs – with a diameter of about 0.01mm” said Mr Matzler.

When the fungus isn’t present, ice still forms, but in a “crust-like structure instead”, according to the Met Office.

So far in 2021, the natural sculptures - also known as frost flowers- have been spotted in Castle Archdale, Florence Court, Castle Coole, Cladgah Glend, Big Dog Forest, Omagh and Knockmany. 

Those who want to view them need to move quickly, because as soon as they are touched by human hands or sunny spells, they’ll be sure to melt away.