The weird phenomenon of red snow!
Recently, videos and photos of red or orange colored slopes have been seen on social, TV and newspapers. What is this all about and, mostly, is it a dangerous phenomenon for winter activity?
Recently, videos and photos of red or orange colored slopes have been seen on social, TV and newspapers, often with quite strange and chromatically varied and interesting effects.
What is this all about and, mostly, is it a dangerous phenomenon for winter activity?
First, let's start by saying that this is an absolutely normal phenomenon that can happen even several times within the same winter especially in certain, more exposed areas.
Sand dust deposited on the snowpack at different altitudes and exposures at the Petit St. Bernard Pass, between La Thuile (Italy) and La Rosière (France) (April 14, 2024).
It is due to the transport of desert sand with southerly winds that pick up the micro grains of sand, lift them into the atmosphere, and deposit them on the ground when the wind speed decreases just enough to not keep them suspended in the air.
This is usually a phenomenon that can be observed on the snows of the foothills closest to Africa and therefore most easily reached by the currents: Apennines, Italian and French Maritime Alps or Pyrenees; but under particular wind conditions, due to strength and duration, sand crystals can also reach the Alps especially on the southern slopes.
For this reason, the last major phenomenon that occurred in late winter 2024 was also noticed in Livigno and all over Alpine valleys.
But what is the effect of this sand deposit on the snowpack, besides the aesthetic aspect?
First of all, it causes a warming of the snow surface because the reddish orange color greatly decreases the ability to reflect light radiation upward (albedo) accelerating the melting process.
Simply put, white reflects heat better, which thus is not retained by the snowpack, which is better preserved; on the contrary, "dirty" snows tend to retain heat and melt faster.
For this reason, lift operators daily check for grass patches on the slopes, and if there are, they are immediately covered to prevent faster snow melting in that area.
But the biggest problem caused by these sand dusts deposited on the surface of the snowpack is when they are covered by new snowfall and thus go to form a weak layer within the snowpack.
The new layer is unlikely to be bonded to the one below, thus generating an excellent flow plane for potential avalanches.
Observation during the outing once again becomes of crucial importance for our safety: natural profiles highlighting within the snowpack a reddish layer of snow should make us think about the slopes we want to travel on the choice of the best trail.
Natural snowpack profiles on a wall and the roof of a house, with a darker layer of snow on the inside: elevation, exposure and thickness of the layer above are pointers that need to be committed to memory, for later recall during the outing.
For those who would like to explore the topic in more detail from a scientific perspective, below is a link to an interesting article by Mauro Valt and Maria Cristina Prola that appeared in the AINEVA journal Snow and Avalanches:
Try the Bluerando app!
With Bluerando, you can save and share your snow activities with friends, check out reports sent by other users, and use the routes in the shared library.
Above all, you can share your location with your travel companions and record your Snow & Avalanche Observations and contribute to everyone's safety.
Ernesto Bassetti
Ernesto is one of the leading snow and avalanche experts in Italy and beyond.
By passion and by profession, he has been involved in mountain safety for over 40 years, with particular attention to the avalanche issue.
He is co-founder, and until 2020 Vice President, of MND Group; important international player in the field of mountain infrastructure and world leader in controlled avalanche release systems.
He is a ski instructor, National Ski Mountaineering Instructor, former director of the Mario Righini Ski Mountaineering School.
He was promoter, co-founder and soul of the "Servizio Valanghe Italiano" (Italian Avalanche Service), of which he held the Presidency for 18 years.
