Decades ago, the Morning Glory pool at Yellowstone National Park was a gorgeous deep blue. But because tourists have thrown coins, rocks, and trash into it for years, the spring has now turned into a sickly yellowish green. Now, a new optics study is shedding light on the pool's unfortunate change of color.

\Interestingly, the new study by researchers at Montana State University and Germany's Brandenburg University of Applied Sciences was never intended to be a project on the chemistry and biology of thermal pools. Instead, the researchers were studying optical phenomena and imaging as it pertains to the diversity of colors in these hot springs. Though it has been known for years that garbage is causing the spring to change color, the new work shows that microbiologists and optical scientists can work together to learn more about the process.

Advertisement

Using a fairly simple optical model, the team was able to recreate the colors and optical characteristics of the springs. They did so by accounting for the pool's spectral reflections caused by microbial mats — complex communities of microbes organized into visible layers — along with other variables such as water depth and temperature, optical absorption, the scattering of water, and the incident solar and diffuse skylight conditions.

By using the new data and previous work done on the physical dimensions of the pool, the team was able to develop a model to recreate the conditions both now and in the past to produce renderings that were similar to actual photographs.

Here's a rendering of what the hot spring looked like decades ago:

And an actual photo of Morning Glory taken in 1966:

Image: William Keller/National Park Service

Here's a rendering of what it looks like today:

An OSA release explains more:

In the case of Morning Glory Pool, they were...able to simulate what the pool once looked like between the 1880's and 1940's, when its temperatures were significantly higher. During this time, its waters appeared a uniform deep blue. An accumulation of coins, trash and rocks over the intervening decades has partially obscured the underwater vent, lowering the pool's overall temperature and shifting its appearance to a terrace of orange-yellow-green. This change from blue was demonstrated to result from the change in composition of the microbial mats, as a result of the lower water temperature.

A general relationship between shallow water temperature (hence microbial mat composition) and observed colors was confirmed in this study. However, color patterns observed in deeper segments of the pool are caused more by absorption and scattering of light in the water. These characteristics – mats having greater effect on color in shallow water, and absorption and scattering winning out in the deeper areas – are consistent across all the measured pools.

Microbiologists are now looking for ways to monitor changes in the biology of these pools and to learn more about why these changes are causing such a dramatic alteration in pool color.

Advertisement

As for returning this pool to its, uh, former glory, that's a different question. Since 2009, a sign has been placed near the pool to suggest that vandalism has caused the springs to become a "Faded Glory." Attempts to clear the pool of debris has been met with mixed results.

Check out the entire scientific study here.

Top image: Joseph Shaw/Montana State University. Other images: Nugent et al./Applied Optics