Grand Prismatic Spring, Yellowstone National Park.
Looking almost alien, and definitely cool, the image below is of a geothermal pool located in Yellowstone National Park, USA. Known as the Grand Prismatic Spring, it is the largest geothermal pool in the National Park; 110m wide, and 37m deep, and the third largest geothermal spring pool in the world. It was named “Grand Prismatic Spring” by geologists from the Hayden Geological Survey of 1871, as the colours reminded them of the way light is dispersed through a prism.
The vibrant colours occur as a result of pigmented bacteria, and microbial mats that grown around the spring. The bacteria present can be differing colours, ranging from green to red depending on the temperature of the water, and the ratio of chlorophyll to carotenoids present. The colours seen at the Spring vary throughout the seasons, and in the Summer vibrant reds and oranges are common, but in the Winter green is seen. The intense blue colour of water is down to three factors; the natural selective absorption of red light wavelengths by the water, the depth of the water and the purity of the water. The water in the center of the pool is sterile due to the high temperatures; the water has been recorded as reaching 70 degrees Celsius.