Page last updated at 00:20 GMT, Wednesday, 30 December 2009

Avalanche risk in Scotland raised by crystals

Hoar surface. Image courtesy of SAIS
Hoar surface photographed by a SAIS team member in Lochaber

Unusually calm and extremely cold weather has raised the risk of avalanches in Scotland's mountains.

Members of the Sportscotland Avalanche Information Service (SAIS) have been monitoring surface hoar, a phenomenon rarely seen in Scotland.

The snow crystals form a slippery layer when buried under snow and are the cause of many avalanches in the Alps and North America, according to SAIS.

Mark Diggins of SAIS said the Northern Cairngorms was one affected area.

He said hoar surface had formed over about 10 days of calm and extremely cold weather.

'Soap flakes'

Normally the crystals, which are created by vapour rising up from layers of deposited snow and then freezing on the surface, are destroyed in a thaw or by high winds.

Mr Diggins said: "What we have got is an unusual climate because of this prolonged cold spell. This has been throwing up some unusual things, one of them being hoar surface.

"The crystals can be quite dangerous if buried by further falls of snow as they form a very, very weak layer.

"The crystals are a bit like soap flakes and create a very slippery layer."

SAIS teams have been checking for hoar surface during routine assessments of avalanche risks in Northern Cairngorms, Southern Cairngorms, Lochaber, Creag Meagaidh and Glencoe.

SAIS provides avalanche forecasts for the five areas which are popular with climbers and skiers online and via mobile phone text messages.

An image of the crystals found in Lochaber has been uploaded onto the service's website.

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