Grand Prismatic Spring

Grand Prismatic Spring glows with rainbow colors in Yellowstone National Park, Wyoming, USA. Measuring about 112 meters across and 49 meters deep, it is the largest hot spring in the United States. Water heated by the Yellowstone volcanic system rises through cracks, dissolving minerals and creating a deep blue center surrounded by orange, yellow, and green microbial mats. Boardwalks and overlooks let visitors see the vivid rings while staying safe from scalding water and fragile crust.

The spring’s colors come from thermophiles—heat-loving bacteria and archaea—that thrive at different temperatures. Near the center, where water reaches nearly 70 °C, only blue light scatters off the clear water, creating a deep turquoise hue. Along the cooler edges, microbes produce pigments like carotenoids that color the runoff channels. Scientists analyze these organisms to understand how life survives extreme heat and acidity, informing studies about early Earth and potential life on other planets.

Grand Prismatic Spring sits in the Midway Geyser Basin, home to other hydrothermal features such as Excelsior Geyser Crater and Turquoise Pool. Ranger programs explain how rainwater and snowmelt seep underground, heat up near magma, and rise back to the surface laden with silica and minerals. Siliceous sinter forms delicate terraces around the pools, so visitors must remain on boardwalks to prevent damage and avoid falling through thin crust.

Researchers monitor the spring using thermal cameras, drones, and water chemistry tests. They track flow rates, microbial diversity, and seasonal changes in color caused by shifting temperatures or sunlight. Airborne lidar surveys map subtle changes in the ground, helping geologists see how hydrothermal systems connect beneath the basin. Weather stations provide data on wind patterns that can blow steam clouds across the boardwalks.

The National Park Service balances tourism with preservation by limiting off-boardwalk access, cleaning litter, and posting multilingual safety signs. Education campaigns remind people not to throw coins or objects into the spring, as debris can block vents and alter water flow. Grand Prismatic Spring’s combination of science, art-like colors, and geothermal power makes it one of Yellowstone’s signature features.