The Grand Prismatic Spring in Yellowstone National Park, Wyoming is the largest hot spring in the United States, and the third largest in the world. It is located in the Midway Geyser Basin.
The bright, vivid colours in the spring are the result of microbial mats around the edges of the mineral-rich water. The mats produce colours ranging from green to red; the amount of colour in the microbial mats depends on the ratio of chlorophyll to carotenoids and on the temperature gradient in the runoff. In the summer, the mats tend to be orange and red, whereas in the winter the mats are usually dark green. The centre of the pool is sterile due to extreme heat. The deep blue colour of the water in the centre of the pool results from the intrinsic blue colour of water. The effect is strongest in the centre of the spring, because of its sterility and depth.
Location: Yellowstone National Park, Wyoming
Photographer: brian swales
