A deep blue eye ringed with yellow, orange and rust-red: Grand Prismatic Spring in Yellowstone National Park looks more like a painting than a pool of water. It is the largest hot spring in Yellowstone, the world's first national park, and one of its signature sights.
Grand Prismatic Spring in numbers
The spring lies in Yellowstone's Midway Geyser Basin, in Wyoming. The National Park Service gives its diameter as 200 to 330 feet (about 60 to 100 metres) and its depth as more than 121 feet (37 metres). It is often ranked as the third-largest hot spring in the world, after Frying Pan Lake in New Zealand and Boiling Lake in Dominica.
The spring pours out roughly 560 US gallons (2,100 litres) of water a minute, at about 160°F (70°C). That steady flow spills outward in shallow, steaming runoff channels, and those channels are where most of the colour lives.
Why the spring is so colourful
The colours come from life. The edges and runoff channels are covered with microbial mats of thermophiles, microscopic heat-loving bacteria and archaea. Each type thrives at a different temperature, so the colour bands work like a thermometer: according to the NPS, colourless and yellow microbes grow in the hottest water, while orange, brown and green types grow where the water has cooled.
The exact shade depends on the balance between chlorophyll and protective pigments called carotenoids. In summer the mats tend to be orange and red; in winter they turn darker green.
The vivid blue centre has a different cause. The water there is sterile and very deep, so what you see is the natural blue colour of water itself, strongest where the column of clear water is deepest.
How Grand Prismatic got its name
Trappers of the American Fur Company noted a "boiling lake" in 1839, almost certainly this spring. The Washburn–Langford–Doane Expedition passed by in 1870 and recorded a nearby geyser that was later named Excelsior. A year later, geologists with the Hayden Geological Survey of 1871 named the spring for its colours, which match the red, orange, yellow, green and blue of light split by a prism.
Boardwalk and overlook: how to see it
There are two classic views, and they are very different.
- Midway Geyser Basin boardwalk: the boardwalk leads right past the spring's edge, past the colourful runoff and through drifting steam. Up close you see textures and the heat; the full circle is hard to take in.
- Grand Prismatic Overlook Trail: starts from the Fairy Falls Trailhead, about 1 mile south of Midway Geyser Basin. It is an easy 1.2-mile (1.9 km) round trip with about 105 feet of climbing, and the viewing platform shows the spring and its colour rings from above. Allow 1 to 2 hours.
Parking at both is limited, especially between 10 am and 6 pm, so arrive early or late in the day. On cold days, steam can hide much of the pool.
Stay on the boardwalks and designated trails: hydrothermal water can cause severe burns, and the microbial mats are easily damaged by a single footprint or scratch.
Compare the mineral terraces at Huanglong, where the landscape has a different geological structure. For clear water in a non-thermal mountain setting, explore Lake Tahoe’s photographic shoreline.
No comments