Black Sand Basin is an isolated group of the Upper Geyser Basin located along the Firehole River about one mile from Old Faithful in Yellowstone National Park. The name derived from the black fragments of obsidian sand that covers the basin of small geysers and colorful hot springs. The most famous of the hot springs is the Emerald Pool. Due to a lower temperature change yellow bacteria and algae grew on the lining of the pool. As the clear water reflects the blues and absorbs the other hues the combination of blue and yellow produced this wonderful emerald green pool. Due to further decrease in the pools temperature there was a change of the bacteria and algae growth so the edge of the pool is now orange and brown. If the temperature continues to decrease the pool could loose its emerald color. | 
