Red Hot 

The Grand Prismatic Springs is the largest hot spring in the continental United States at 300 feet in diameter and 160 feet deep. It lies within the Midway Geyser Basin of Yellowstone National Park in Wyoming and with only an average temperature of 160 degrees it is not the hottest in Yellowstone National Park.

Beings At Grand Prismatic Spring That honor is reserved for the geysers in the Norris Geyser Basin of Yellowstone where temperatures can be as high as 250 degrees. Though documented by white fur traders exploring as early as 1839, the Grand Prismatic Spring was not officially surveyed until the Hayden Geological Survey of 1871. Early fur traders called the Yellowstone area "where Hell bubbled-up through". Named for its rainbow like dispersion of colors similar to an optical prism with colors of red, orange, yellow, green and blue, the vivid colors are for the most part due to pigmented bacteria that grows around the edges of the mineral-rich water. The center of the pool is sterile and consistently deep rich blue. Colors on the edges change by season depending on which bacteria will thrive in certain temperature ranges. This photo was taken at sunset around the extreme edges of the springs at least 300 feet from the pool center located on the other side of the walkway beyond in this photo. The silhouettes of the onlookers on the floating wooden walkway was too good to pass up in this photo shot with a 35mm lens, shutter at 1/125th at f/13, with an ISO 500 due to the low light conditions and with flash to highlight the earthen crust microbial mats in the foreground. These mats are very thin in places and puncture easily by mere footsteps.

There have been an estimated 26 deaths since 1890 in Yellowstone directly related to geo-thermal areas, many more for other reasons. One of the saddest is the story of a 24 year-old California man who in 1981 dove head-first into the Celestine Pool's 202 degree water to rescue a friend's dog who became trapped in the pool of boiling water after falling off the adjacent wooden walkway. The man managed to swim back to the pool edge with the dog and when helped out by bystanders he was blind with third degree burns over his entire body as was the dog. The dog did not survive. He said to onlookers when he was helped out: "That was a very stupid thing I did but I had to try to help the dog." He died the next day in a Salt Lake City hospital.