I wasn't expecting to even find snow when I climbed Ben Nevis in mid-July, let alone watermelon snow! As we approached the plateau at the summit, a big bank of snow began to come into view through the fog. As we got closer, the faint but distinct red accents of red snow algae became visible and I had my second ever encounter with watermelon snow! As we continued our hike to the summit, further snow patches came into view, also boasting watermelon snow.
Watermelon snow is a red coating on snow, caused by a red-coloured algae that favours the cold and harsh growing environments. The algae grows on the snow and lays dormant during the winter, buried under a thick layer of winter snow, but appears during the summer, normally on alpine and arctic snows where it blooms in the warmer temperatures and meltwater. The algae is very interesting in that it helps to melt the snow by lowering the albedo (by darkening the snow's surface) causing the snow to melt quicker in the places where the algae is, allowing the algae to access the liquid water that it needs to survive. The red colouring may be useful to the algae as solar protection, as it lives in such hostile, often high altitude environments where there's less shade or atmospheric protection from the sun.
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