The Black Sand Basin is home to several hot springs and geysers. The most popular of these is the Emerald Pool. The pool gets its color from yellow and orange bacteria that grow on the lining of the pool. The yellow color combines with the deep blue of the clear water to produce the green color for which the spring is named.
Rainbow Pool is another hot spring that is located on the Black Sand Basin. Algae and bacteria growing along the edge of the pool produce a variety of colors and are responsible for the name of this hot spring.
Next door to the Rainbow Pool is Sunset Lake. Don't be fooled by the name. Sunset Lake is a shallow pool with yellow and orange algae and bacteria growing on the edges, making it appear the colors of a sunset. This pool has occasionally erupted over the past 60 years. The eruptions bring up hot water which kills the bacteria and algae, but as the pool cools after the eruption the colors return.
There are also a couple of geysers in the Black Sand Basin. Spouter Geyser is supposed to be the most regular erupting geyser on the Black Sand Basin. However while we were there Spouter was a spoiler and was very quiet.
The run off from the Spouter Geyser has created the neighboring Opalescent Pool. This shallow pool was once a boiling spring, but by the 1950s it had all but dried up. Then the Spouter Geyser began to erupt giving new life to the Opalescent pool.
Even though the Spouter Geyser was quiet while we were at the Black Sand Basin we did get to see the Cliff Geyser erupt. The cliff geyser has a much more irregular eruption schedule with eruptions occurring usually only a couple of time a day, although it also been known to go dormant for weeks at a time.