Black Sand Basin is one of Yellowstone National Parks small geothermal areas with colorful pools, hot springs and geysers. The name "Black Sand" comes from fragments of black Obsidian found across the basin. Obsidian is a natural form of volcanic glass which formed when lava cools rapidly.
Located 1 mile northwest of the popular Old Faithful geyser, it can be reached two ways, by driving straight to the basin or by walking the 1/2 trail from Daisy Geyser at Upper Geyser Basin. Getting around the Black Sand Basin is fairly easy. A short and easy 0.4 mile boardwalk starts at the parking area.
There are many large and small, prominent and unnamed geysers across the basin. These are some of the features that can be easily spotted from the boardwalk.
Rainbow Pool is one of the most colorful pools in the park. It is a large multicolored pool with blue center and colorful edges caused by cyanobacteria. This pool hasn't erupted in many years.
The Microbial Mats, also known as "Bacteria Mats", seen across all the basins are a result of microscopic organisms and algae that thrive on the hydrothermal features. The iron and mineral rich conditions, and temperatures in/around pools, geysers and hot springs are ideal for their survival. Flies and insects feed on these mats, which in turn are hunted down by predators like wolf spiders. Warmer ground temperatures also play a critical role in winter survival of Yellowstone's large mammals.
Cliff Geyser sits on the edge of Iron Spring Creek just before the footbridge. Its eruptions are highly unpredictable, it can erupt every few minutes or stay dormant for weeks or even years. You can tell it is about to erupt when its crater fills up with water.
This colorful pool is one of the main attractions at Black Sand Basin. The pool's center is emerald green color which it is named for, and has a yellow and orange outer ring. The outer colors are a result of yellow bacteria and algae growth.
This is another colorful and large hot spring. Its high temperatures cause steam clouds which often obscure the pool, making it difficult to see any activity. It has had eruptions of up to 30 feet in the past.
A small spouter named after the orange-red deposits around its vent. Cinnamon Spouter was erupting continuously when it was first discovered. Over the years it has decreased, and now has short to long intervals between spouts.
It is a shallow, large, hot, green-blue pool. Eruptions are very infrequent, and minor ones have been recorded over the years.
Spouter Geyser, once a continuous geyser, still erupts constantly shooting up to seven feet high, with only short intervals. The vent is surrounded by whitish-grey sinter.
It is a beautiful blue pool which used to be a boiling spring. Over the years the spring dried out and now holds water from the run-off of Spouter Geyser. Water overflow eventually killed lodgepole pines surrounding it, which now stand as skeletons partially covered in silica. Cooler temperatures allow for brown bacteria to grow around it.
White Sand Spring:
It is a small shallow spring with occasional eruptions.