Seventy years ago the geothermal pools of Yellowstone tended to have a uniformly deep blue colour. Temperatures were higher because there were fewer tourists at the site. Over the years, coins, trash and rocks tossed into the pool have covered the natural vents. This has lowered temperatures in the pool and caused them to turn to an orange-yellow-green colour.
‘When we started studying [the pools], it was clear we were just doing it for fun,’ says Michael Vollmer from Montana State University. The initial research may have been light-hearted, but the team soon discovered there was very little existing scientific literature on the subject.
Vollmer worked with his colleague, Joseph Shaw, at the university’s ‘Optical Technology Center’ to work out a mathematical model showing how chemical and physical variables in the pool created the stunning effects.
The research used digital SLR, long-wave thermal imaging cameras and handheld spectrometers, and the work let the researchers reproduce the colours and characteristics of the hot springs right back to a time before tourists had polluted the pools. The next step for the team is to collaborate with experts on pool biology to better understand how changes in microbial life lead to the changes in colour.
Shallow water temperature tends to change the colours in the pools, but patterns in deeper segments are caused by more absorption and scattering of light in the water. ‘What we were able to show is that you really don’t have to get terribly complex – you can explain some very beautiful things with relatively simple models,’ says Shaw.
This story was published in the February 2015 edition of Geographical Magazine