The whole walk to the source of the Severn was in fog, but it wasn't until about 400 metres above sea level that some of the plants began to have a coating of rime ice. By 600 metres, everything was rime-coated, including the path markers, peat hummocks and the source of the Severn itself. The largest trail of rime ice I measured was around 25mm thick, and supported by only a very thin piece of grass.
Rime ice is deposited by freezing fog, and grows into the direction of the wind. If left to grow, rime ice can grow to great lengths, sometimes more than 50 cm on mountains etc. This directional effect means that the objects that the ice grows on can shelter other objects, or the downwind side of the plant for example. In all of these photos you can see which direction the wind was blowing, with the rime spikes pointing into the wind, and in lots of them you can see this sheltering effect.
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