Emerald Spring

Emerald Spring, a hot spring in Yellowstone National Park’s Norris Geyser Basin, is known for its clear green color, created when sunlight makes blue light appear against yellow sulfur around the pool. Philetus Norris, park superintendent from 1877 to 1882, originally named it Emerald Geyser, and the U.S. Geological Survey renamed it Emerald Spring in 1930. In 1892, physicist Robert W. Wood startled onlookers by secretly adding fluorescein to the water. About 27 feet deep and around 83.3 °C, it is usually calm, but it can turn turbid and erupt, most notably in 1931 when bursts reached 60 to 75 feet.

Wyoming · United States