Imaggeo on Mondays: Green river

Water dyed green runs down a thermokarst during a scientific experiment, by Simon Gascoin, distributed by EGU under a Creative Commons licence.

Thermokarsts occur when solid permafrost melts and soil gives way forming pitted, irregular lands surfaces. They are common in the Arctic, as well as the Himalayas and Swiss Alps. To study them, scientists trace the water using fluorescence dyes, temporarily creating water flows of exotic colours, like the bright green one in this Imaggeo photo.

This photo was taken by Simon Gascoin, a researcher at the Centre d’Etudes Spatiales de la Biosphère. “I took this picture during a field experiment near the Tapado glacier in the Andes of north-central Chile. All of the meltwater flowing from the glacier snout infiltrates in a thermokarst underground network and reappears in a proglacial spring located about 2km further downhill. The objective here was to determine the time of transfer between the infiltration hole and the spring, however, this particular experiment failed as we never observed the dye at the outlet! The hydrological dynamics in the Tapado watershed are currently being investigated by the CEAZA institute in Chile and Hydrosciences Montpellier,” he recollects.

In the context of environmental change, thermokarsts serve as effective geo-indicators of current and historic warming temperatures. However, they may also be directly formed by human activities, such as drilling and road construction.

See more of Simon Gascoin’s photography at

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

Bárbara Ferreira was the Media and Communications Manager of the European Geosciences Union from 2011 to 2019. Bárbara has also worked as a science writer specialising in astrophysics and space sciences, producing articles for the European Space Agency and others on a freelance basis. She has a PhD in astrophysics from the University of Cambridge.

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