Black Sand Basin is an isolated group of the Upper Geyser Basin located along the Firehole River about one mile from Old Faithful in Yellowstone National Park. The name derived from the black fragments of obsidian sand that covers the basin of small geysers and colorful hot springs. The Rainbow Pool, 27 feet deep, displays the colors of a rainbow along its edges. Algae and cyanobacteria cause the varied colors. In 1948 the pool erupted and reached a height of 25 feet. The last eruption was in 1973. |
