Sand dunes are a familiar sight in deserts and along beaches. Established theory describes how wind direction affects the dunes’ formation, and their size and shape reveal clues about the surrounding environment. Such properties are much less documented for dunes made of snow. “It is difficult to be certain, but there are no more than 10 or 20 papers on snow dunes in the whole scientific literature,” says Ghislain Picard at Grenoble Alpes University in France. The lack of understanding makes it difficult to predict how snow dunes affect accumulation and erosion processes in places like Antarctica.
Picard became interested in snow dunes while working on an unrelated project in Antarctica. He was dragging an instrument along the ground, taking meter-scale measurements of snow height, when he noticed 30-m-long oscillations in the data. Despite the ground looking flat to his eye, the instrument had detected short dunes. Now Picard, Marine Poizat, and their colleagues have analyzed satellite imagery and found that about 90% of Antarctica is covered by snow dunes.
Obtained from the Landsat 8, Sentinel-2, and Pléiades satellites, the images reveal that most Antarctic dunes are longitudinal dunes, meaning that they are elongated in the direction of the prevailing wind. The dunes are usually less than a meter high, and they can be up to 5 m wide and multiple kilometers long. Their limited height makes them difficult to see from the ground. Picard and Poizat worked with sand dune theorist Clément Narteau, whose group developed a model to predict the orientation of dunes using a function of the wind.
Longitudinal snow dunes form when snow carried along the ground by the wind creates small ridges. More snow is pushed up along the ridge, and it comes to rest when it loses momentum on the leeward side. Because of slight variations in wind direction, snow builds up on both sides of the ridge. As their sand counterparts do, snow dunes stretch in the same direction as the mean dominant wind. The prevalence of dunes formed via elongation suggests that there’s not a lot of snow that is available for dune creation. For both sand and snow dunes, greater amounts of mobile particles tend to form taller dunes that are oriented perpendicular to the prevailing wind direction.
Picard says he wasn’t surprised by the potential scarcity of mobile snow in the continent’s interior, where the air is dry and snowfall averages less than 10 cm per year. He found it unexpected, however, that the same dune formation occurs in the coastal regions, which are more humid and see at least a meter of snowfall annually. The snow that falls appears to bond quickly to other ice crystals and thus becomes unavailable for movement. That is a phenomenon not seen in sand dunes and that Poizat says needs to be better understood before snow dunes can be used to inform models of surface processes. (M. Poizat et al., Nat. Geosci., 2024, doi:10.1038/s41561-024-01506-1.)
