Our directory of things of interest

After the tourists

  • Written by  Tom Hart
  • Published in Water
A geothermal pool within Yellowstone National Park A geothermal pool within Yellowstone National Park Shutterstock
21 Feb
Yellowstone National Park is home to some astounding geothermal pools. These colourful natural phenomena occur due to interaction between underwater hot vents and bacteria that grow in lawns across the pools

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

Related items

Geographical Week

Get the best of Geographical delivered straight to your inbox every Friday.

Subscribe Today

Adventure Canada


Aberystwyth University University of Greenwich The University of Winchester




Travel the Unknown


Like longer reads? Try our in-depth dossiers that provide a comprehensive view of each topic

  • National Clean Air Day
    For National Clean Air Day, Geographical brings together stories about air pollution and the kind of solutions needed to tackle it ...
    The Air That We Breathe
    Cities the world over are struggling to improve air quality as scandals surrounding diesel car emissions come to light and the huge health costs of po...
    Diabetes: The World at Risk
    Diabetes is often thought of as a ‘western’ problem, one linked to the developed world’s overindulgence in fatty foods and chronic lack of physi...
    The Nuclear Power Struggle
    The UK appears to be embracing nuclear, a huge U-turn on government policy from just two years ago. Yet this seems to be going against the grain globa...
    The true cost of meat
    As one of the world’s biggest methane emitters, the meat industry has a lot more to concern itself with than merely dietary issues ...


NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in PLACES...


Public transport in India could be on the verge of…


To retrace the route of the fur voyageurs on the waterways…


IPCC Cities and Climate Change Conference: Alberta host dresses non-renewable…


Increased carbon dioxide is affecting freshwater ecosystems


The latest laser scanning technology reveals new insights into the…


Deforestation is having an unexpected effect in the Amazon: fewer…


The iconic Douglas fir tree, familiar to fans of the…


Rocky Mountain forests are not regenerating after wildfires


Cape Town is edging closer to ‘Day Zero’, the long-feared…


Ongoing restoration projects are breathing new life into Florida’s Everglades


Despite protests, an experimental pedestrianisation system is proving to be…


National Archives map historian, Rose Mitchell, highlights some of the…


An expedition into the Jordanian desert is helping teachers and…


Trivia fans take note, Mount Hope in the British Antarctic…


An enormous hydropower development in Ethiopia is expected to put…


From nuclear warnings to whether your favourite band will ‘make…


New maps of global reptile distribution reveal significant gaps in…


Indigenous conservation schemes in Peru can be more effective than…


How are the EU member nations faring in the fight…


Violence against women violates human rights, and the lack of…