A hot spring's color often indicates the presence of minerals. In a clear blue pool, the water is absorbing all colors of sunlight except one, blue, which is reflected back to our eyes. Here in Emerald Spring's pool, another factor joins with light refraction to give this spring its color. The 27-foot (8 meter) deep pool is lined with yellow sulfur deposits. The yellow color from the sulfur combines with the reflected blue light, making the hot spring appear a magnificent emerald green.
Hot spring water can dissolve and transport sulfur from underground. The mineral can deposit and crystallize at the earth's surface, sometimes in hot spring pools.
Did You Know?
Even though the animals of Yellowstone seem tame they are still wild. Feeding the animals is not permitted in any way, and all visitors must keep 100 yards away from wolves and bears, and 25 yards from other animals.