The striking limestone terraces of Yellowstone National Park in northwestern USA have long been a source of wonder and intrigue, and were central to its inscription as the world’s first national park in 1872. Now computer models have shed light on exactly how the varied pattern of pools is achieved.

In a paper published in Nature Physics, physicists John Veysey and Nigel Goldenfeld of the University of Illinois at Urbana Champaign, suggest that the irregular pattern of pools is formed by the variable water flow from geothermal springs and the subsequent accumulation of calcium carbonate along terrace boundaries, rather than by the microbial or mineral makeup of the spring water,
as had been widely assumed.

‘The ponds and terrace steps are bigger near the vent and get smaller far away,’ said the physicists. ‘Our research has shown that the landscape evolves by a process called inundation, whereby a fast-growing downstream pond floods its upstream neighbour.’ It’s this drowning, said the researchers, that governs the size and shape of the terraces.

Working at Mammoth Hot Springs, the team observed what was happening and then developed a computer model to predict the distribution and appearance of the calcium carbonate terraces. Over a subsequent two-year period, these predictions were verified using time-lapse photography of the area.