Jeremy Ashcroft

Trail’s mountaineering editor is also author of Britain’s

Highest Mountain Walks, pb Collins. He knows the UK hills better than his own reflection.

Cornices are formed when wind-driven snow is blown over sharp edges and deposited on the lee (downwind) side by the swirling air that the change in angle creates. These snow ledges are common above cliffs and steep slopes on summits, plateau edges and along the side of ridges. They can also be found in other areas of angle change, such as hanging over ghylls or burns. Their size can vary greatly and can be very difficult to determine, both from above and below. The overhanging nature of cornices makes them unstable, and although they are at their deadliest when freshly formed or during a thaw they should always be treated with caution. When cornices collapse the breakoff point is generally not in line with the slope below. Often the fracture is angled well back, and can drag snow from ground that you may consider to be safe and away from the edge. From above, particularly in poor visibility, cornices can be hard to spot as their lip often appears to merge with the whiteness of the slopes below, and unless there is a strong shadow they become invisible. It is important when passing known or suspected cornices that you give them a very wide berth, and don’t head onto them even if you think you know where the ground edge is.

How can I spot a cornice? Graham Byrne, Sutton Coldfield