Rare Pancake ice phenomenon on reservoir near Loch Lomond

Advertiser reader Charlie McGinn noticed the unusual formations on the Finlas Water reservoir in the hills above Luss. 

Charlie shared them with other members of the Helensburgh Advertiser Camera Club group on Facebook.

He said: "Apparently this is a rare phenomenon in Scotland. It's the first time I’ve managed to see it."

Pancake ice on the Finlas Water reservoir, by Charlie McGinn (Image: Charlie McGinn)

Pancake ice normally forms in rough seas around the Arctic and Antarctic, but can form in some lakes and rivers.

The formations are not often seen in Scotland, but have been reported in the past on the River Helmsdale in the Highlands, the Bladnoch River in Galloway and even, a couple of years ago, on the Water of Leith in Edinburgh.

What causes 'pancake ice'?

Tiny needle-like crystals called 'frazil crystals' rise to the surface and accumulate together.

In calm water these typically form a greasy film that freezes into a flat surface ice.

However, in rough or choppy water, these crystals congeal together into slushy, circular discs.

As these discs bump into each other and are buffeted by the water, they develop ridges and raised edges, giving them a distinctive dinner plate appearance.

Pancake ice on the Finlas Water reservoir, by Charlie McGinn (Image: Charlie McGinn)

In the polar seas these can sometime have a thickness of up to 3.9 inches and diameter of between 12 inches to nine feet.

Eventually the plates fuse together to form consolidated sea ice that can have ridges that are up to 60 feet thick.

Judging by Charlie's photos, the 'fusing' process may have happened rather sooner on the Finlas Water - and we have our doubts that these discs will ever quite reach those dimensions - though the 'pancake' formations can be clearly seen.

Temperatures in the area are expected to remain close to, or even below, freezing point for the next few days, with weather warnings in place for snow and ice in the area at various points until Thursday - meaning it may be a while yet before the ice melts on this particular surface.