Fall is marked with a change in colors. The leaves start to change, grasses and plant life withers away, and the days get shorter. It’s all a sign that winter is coming, like it or not. While those color changes are all very well known, the changes that take place in the hot springs of Yellowstone National Park are a bit more obscure.
Yellowstone’s hot springs are full of microscopic organisms called thermophiles, thriving in the extreme heat while creating vibrantly colored communities. Some survive in pools of water as acidic as the fluids in your car battery, some form layers of what looks like molten wax on steaming alkaline pools, and others live in rotten-egg smelling sulfuric caldrons.
Many of these thermophiles change color for a multitude of reasons, but temperature changes appear to be the most influential. In waters with temperatures as high as 167°F, for example, some cyanobacteria might appear a yellow-green. When that water cools, those microbes turn towards orange, rust, or brown.
Some of Yellowstone’s microbes change with the seasons, too. In the winter, darker colors allow for more light absorption. Those darker colors are visible in the first picture below. However in the summer, when sunlight is more abundant, those same microbes tend to be quite a bit paler. The second picture, with a crowd on the boardwalk, shows those lighter colors quite clearly.
