Grand Prismatic Spring Reflections Poster

"Grand Prismatic Spring Reflections, Yellowstone National Park, Wyoming" by Catherine Sherman. The sun appearing from behind clouds is reflected in the runoff waters of the Grand Prismatic Spring in Yellowstone National Park. The Grand Prismatic Spring, in the Midway Geyser Basin, is the largest hot spring in the United States, and the third largest in the world. The beautiful colors in the spring itself weren't visible on the day we visited because steam obscured the pool, but we could see the colorful bacterial mats surrounding the spring. The vivid colors in the spring are the result of microbial mats around the edges of the mineral-rich water. The mats produce colors ranging from green to red; the amount of color 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; in the winter the mats are usually dark green. The center of the pool is sterile due to extreme heat. The deep blue color of the water in the center of the pool results from the intrinsic blue color of water.