Morning Glory Spring, Yellowstone National Park, United States

The distinct color of the pool is due to bacteria which inhabit the water. On a few rare occasions the Morning Glory Pool has erupted as a geyser, usually following an earthquake or other nearby seismic activity.
Vandalism
Several entryways have been clogged due to objects being thrown in by tourists, reducing the hot water supply, and in turn altering the overall appearance of the pool. Several attempts by park officials to artificially induce eruptions to clear the pool of debris and clear blocked entryways have been met with mixed results. An interpretive sign, placed near the pool by the park service, discusses the damage caused by ignorance and vandalism and suggests that Morning Glory is becoming a "Faded Glory."