Tourists from all over the world flock to Yellowstone’s geothermal pools, like Morning Glory (seen above), to witness their brilliant hues. But according to a new study, those same visitors completely changed the pools’ appearance.
The study, by researchers from Montana State University, used a mathematical model to analyze measurements taken at geothermal pools across Yellowstone to reconstruct what the pools might have looked like before humans first set foot in the area.
What they found at Morning Glory was stunning: Before Yellowstone opened its doors to millions as a national park in 1872, the pool was actually a clear, brilliant blue, Phys.org reports.
So what did tourists do that caused the shift in color? It all starts with the science.
Water in the pools — heated by vents that tap into the Earth’s superheated mantle — reaches temperatures in excess of 180 degrees Fahrenheit, a perfect environment for heat-loving bacteria known as thermophiles that coalesce on rocks based on water temperatures to form distinct coloring patterns.
Simply put: Different colors represent different groups of thermophiles attracted to a given spot by different water temperatures.
Over the last 140-years-plus, tourists visiting the site tossed coins and other debris into the pools, blocking off vents into the earth below. Those blockages lowered the temperature in the pools, particularly Morning Glory, changing what type of thermophiles could thrive in the water.
The study’s model projected just what color the shallow depths of the pool would’ve looked like before that temperature change, when Morning Glory was much warmer, compared to what the pool looks like now.
The deepest parts of the pools remain a dark blue because of the way light interacts with water, the study’s authors said.
“The pool center — though presumably covered by the yellow mat — appears deep blue, indicating that the pool is deep enough that backward-scattered sunlight from the water is the dominant component of upwelling light,” the study said in part.
As the Los Angeles Times details, the study certainly changes the context of the words in the first survey conducted in the area in 1871, which said of the springs: “nothing ever conceived by human art could equal the peculiar vividness and delicacy of color of these remarkable prismatic springs.”
A color that, no doubt, was a peculiar, vivid, delicate blue.
MORE ON WEATHER.COM: The Many Colors of Yellowstone’s Geothermal Pools