Yellowstone’s Grand Prismatic Spring
You cross a bridge over a burbling stream, clamber up a copper-toned hill and suddenly there it is: Yellowstone’s Grand Prismatic Spring. Standing on a wooden walkway, I inhale the warm, earth-scented vapors that glide across the turquoise water. Otherworldly? Yes. But, surprisingly even here, in this stunning but inhospitable place, there is life and things are growing.
First described in 1871 by the Hayden Expedition, the Grand Prismatic Spring is the third largest hot spring in the United States. Veiled in steam, it bubbles like a bathtub, offering a glimpse now and then into the churning caldron. The deep blue pool is impressive, but more surprising still are the tentacles of golden yellow, burnt orange and metallic green that fan outwards from the roiling waters, carving kaleidoscopic paths across the scorched soil.
Grand Prismatic Spring from new overlook trail
Upon seeing the spring for the first time, Ferdinand Hayden (the leader of the Expedition) wrote:
Nothing ever conceived by human art could equal the peculiar vividness and delicacy of color of these remarkable prismatic springs.
It’s enough to make your head spin.
Yellowstone’s hot springs
There are different kinds of hot springs at Yellowstone National Park. Grand Prismatic Spring is one. Old Faithful is another. Both result from groundwater that has been heated by molten magma and risen to the surface. In the case of Old Faithful, however, the hot water encounters blockages on its way up. This produces the famous geyser’s explosive eruption of steam.
By contrast, the Grand Prismatic Spring is produced by hot water that rises to the surface through cracks in the earth’s crust. This allows for a continual flow of water that rises, cools and falls to the earth only to rise again.
Looking into the turquoise depths of the spring
Grand Prismatic Spring
Pouring almost 500 gallons of scalding water per minute into nearby Firehole River, Grand Prismatic Spring is the largest and most brilliant colored of Yellowstone’s many hot springs. The high temperature of the spring (estimated at around 160 degrees F) is responsible for the steam that hovers 24/7 above the crater.
Due to this cycle of heating, cooling and re-heating, the spring has developed rings of varying temperatures. The hottest water, which is located in the center, is too extreme for living things. However, as the water spreads outwards, it gradually cools, allowing for conditions more amenable to life to develop.
Bands of color at Grand Prismatic Spring
Happily, the viewing boardwalk provides safe passage for we humans atop the smoldering landscape. Embroidered with signs warning against the dangers of erring from the prescribed path, it features stories of how people have been scalded, children killed and family pets sucked into the vortex. Even standing too close to the spring can cause intense burns.
The viewing boardwalk at Grand Prismatic Spring
So how can life exist in such harsh conditions? The answer lies in the prismatic colors. Each of these stunning hues harbors billions of colorful microorganisms that live in the spring’s runoff channels. These ‘extremophiles’ (so named for their ability to live in conditions that were once thought too hot to host life) are not only surviving, but thriving, happily assembled in thick, microbial mats.
Forests in miniature
Microbial mats may not sound all that interesting until you consider that each of these burgeoning communities is in fact a miniature ecosystem functioning much like a forest. There’s a ‘canopy’ of microbes performing photosynthesis. And, there’s an ‘understory’ of organisms playing the crucial role of decomposition and recycling of nutrients back to the canopy.
The rainbow of colors that the mats produce depends on the temperature of the water. In the summer, the mats tend to be brown, orange or red and in the winter they tend to be dark green.
Microbial mats radiating outwards from Grand Prismatic Spring
Cynobacteria, marine bacteria that obtain their energy through photosynthesis, are one common organism found growing by the Grand Prismatic Spring. In the world’s oceans, cynobacteria occupy an important position at the bottom of the food web. At Yellowstone, however, they have had to make some ecological adjustments. These are evidenced in the distinctive yellow/orange color of the spring’s outer ring.
Specifically, a certain strain of cynobacteria called synechococcus has learned to survive the heat by adjusting its ratio of chlorophyll to carotenoids. Yellowstone’s extreme temperatures, high altitude sun and lack of shade can quickly overwhelm the photosynthetic process. So synechococcus manipulate their photosynthetic pigments to reflect only certain wavelengths of visible lights. They do this by employing carotenoids as shields, which results in their summertime yellow/orange color.
Close-up of some of the microbial communities
And so it goes. As you move further from the spring, more and more lifeforms can be found. Synechococcus is now joined by chloroflexi bacger, whose combined colors read as orange. Finally, as the temperature cools, the communities of bacteria at the furthest points produce the darkest color, a molten shade of coppery-brown.
View of spring from bridge
Hard to believe these mini orange and brown ‘forests’ are existing right under our very noses. Life is pretty amazing.