Just because they’re bacteria doesn’t mean they can’t be
beautiful.
The heat-loving bacteria in Yellowstone National Park’s Grand
Prismatic Spring, which is featured on this section’s cover, get
credit for making it the most colorful hot spring in the park.
From above, Grand Prismatic is a large oval splash of cornflower
blue on the ash-white landscape of Middle Geyser Basin, edged by
flowing, armlike strands of yellow, orange and red.
Grand Prismatic is the largest and deepest hot pool in
Yellowstone, measuring 250 feet by 350 feet and dropping to 132
feet at its deepest. About 560 gallons of water at 188 degrees
gushes from the springs every minute.
As the water passes through fissures underground, it picks up
silica, one of the components of glass.
When the hot water cools at the edges of the springs and runs
over the rim, silica is deposited, creating the white rock cone
around this spring as well as others in the park.
The springs at Mammoth differ; the water there contains calcium
carbonate.
Although Grand Prismatic is the largest hot spring in North
America, it is only the third-largest in the world. New Zealand has
the two that are larger.
But the Kiwis’ hot springs can’t compete with Grand Prismatic
for colorful grandeur.
In the center of Grand Prismatic, where the pool is deepest and
too hot for bacteria, the water is a deep blue that looks as if the
sky has been captured on Earth. As the water cools toward its
edges, different thermophilic bacteria find comfort zones where
they make their living.
From blue the spring fades to light blue, then green, yellow,
orange and red.
Often around nonacidic springs and geysers are oxygen-producing
bacteria that rely on photosynthesis.
The color given off by Grand Prismatic’s bacteria is a pigment
that they use as sunscreen. By the time the water gets to the edge
of the spring, it has cooled to about 147 degrees.
In 1899, a tourist guide described Grand Prismatic as “so
dazzling that the eye cannot endure it.”
The spring was originally called Prismatic in 1878 “on account
of the brilliant coloring displayed in it.” The “Grand” was tacked
on later.
How to visit
A half-mile boardwalk accesses the east side of Grand Prismatic
Spring as well as Excelsior Geyser, which was once the largest
geyser on Earth.
The parking area for the boardwalk is about 11 miles south of
Madison Junction or five miles north of Old Faithful. There's also
a parking area farther south that accesses the Fairy Falls
trail.
Hikers and bike riders can take this route to access a hill
overlooking Grand Prismatic Spring and then continue on to the
Fairy Falls trail turnoff.
No bicycles are allowed on the 1.6-mile trail to Fairy Falls,
but cyclists can ride to the Fountain Flat Road and the Nez Perce
Creek picnic area, a 5-mile route one way.
