Algae blooms, also known as “the blood of glaciers” or “watermelon snow”, are present everywhere in mountains and polar circles, but remain poorly understood. A new study reveals that their development depends on the speed of snowmelt.

Algae blooms are caused by the proliferation of a micro-organism, Sanguina nivaloides. In the Alps, these massive blooms generally occur in late spring, at high altitudes, particularly on old snow, but the factors influencing this dynamic remained unknown.

By analyzing satellite images, this new study reveals that prolonged snowmelt favors the development of these algae in this mountain range. What do we know about the occurrence of these blooms, and how can we explain these results? Answers from Léon Roussel, PhD student at the Centre d’Etudes de la Neige in Grenoble, at the Centre National de Recherche Météorologique attached to the CNRS and Météo France. He is the first author of this study, published in PNAS.