Environment

Unusual weather shows at high altitude

The strange phenomenon of colored snow: it's not sand but it's micropowders, the videos

The micro-dust arrives from the Sahara brought by the southern winds and dyes the snow the color of the desert

04/01/2024

It is a rare event but not as rare as it seems: between the end of winter and the beginning of spring it can happen that the snow turns yellow or orange. The cause is not the actual sand of the Sahara but the micro-dust that compose it, whose microscopic particles are prey to the winds that blow, from south to north, from the deserts of Africa and are easily transported to great heights where it forms the snow that then falls on the Alps.

The pink snow

The pink or red colour, which can sometimes color the snow, is instead due to microorganisms, algae in particular, which proliferate in the snow, of which the most common species is Chlamydomonas

nivalis.

The coloring is caused by various carotenoids, including astaxanthin. These carotenoids are produced in unfavorable environmental conditions by the algae for protection, for example in the event of the emanation of strong UVA rays which occur at high altitudes or due to the effect of the strong light produced by the luminous reflection of the snow.

Layers of this snow are deposited on top of the previous snow and are then covered by new snowfalls, leaving very precise traces in the stratification of the snow cover. Darker than normal snow tends to melt faster because it absorbs more UV rays from the Sun.