Volcanic Springs

Geysers, Hot Springs,
Mud Pots, and Fumaroles

Midway Geyser Basin, Excelsior Group

Excelsior Group is by far the most popular destination within Midway Basin and therefore often quite crowded. The loop walk allows a more or less close look on the four main features. Exception is Indigo Spring, which is not visible from the boardwalk.

After crossing Firehole River, the trail runs along Excelsior Geyser and its runoff. Standing next to the oval, more than 90 m (300 feet) wide crater is very impressive, even if you can catch only a glimpse of the feature through the dense steam. This already indicates that Excelsior Geyser is really hot, around the boiling temperature of 93 °C (199 °F) at a respectable discharge rate of 250 liters per second (4,000 US gallons per minute). In the 1880s eruptions of Excelsior were among the largest of any Yellowstone geysers, reaching up to 90 m (300 feet) high. Unfortunately, the last eruptions occurred in 1985, and they failed to reach the maximum size.

Excelsior Geyser (roll mouse over picture):

Excelsior Geyser Yellowstone

Excelsior Geyser
As mentioned before, Indigo Spring southeast of Excelsior Geyser cannot be seen from the loop walk. The best observation spot is the top of Midway Bluff, a hill east of the highway, providing a spectacular sight over the entire group and a suitable viewing angle for Indigo. But the beauty also has a dark side. Probably it was the 88 °C (191 °F) hot Indigo Spring, into which a 52-year-old man from Texas fell and was scalded to death in August 1928. This happened decades before the first boardwalks were built in the Excelsior Group.
(Update 2016: Midway Bluff has been permanently closed to public access since summer 2016.)

Indigo Spring as seen from Midway Bluff in 2013:

Indigo Spring Yellowstone

Indigo Spring, George H. Brown, Yellowstone
Grand Prismatic Spring is the icon of Yellowstone. Dimensions of 113 m (370 feet) in maximum diameter and approximately 49 m (161 feet) in depth make it the largest hot spring of the park and one of the largest worldwide. If you now wonder how the depth measurement of such a large hot spring could be done, the answer is as simple as scary. In 1994 park geologist Rick Hutchinson navigated the "Little Dipper", a small row boat made of fiberglass-coated plywood, over the scalding hot water to the center of the spring and plumbed the pool's deepest point. Probably, not many people did envy him for that hell of a job.

Grand Prismatic Spring (roll mouse over picture):

Grand Prismatic Spring Yellowstone

Grand Prismatic Spring
At a surface temperature of 70 °C (160 °F) Grand Prismatic Spring is not generating as much steam as Excelsior Geyser, but if you want to spot larger parts of the springs water surface, you should pick the hours beween noon and late afternoon of a warm, sunny day. One of the most surprising facts and the origin of its name is that by a freak of nature the color sequence from center of Grand Prismatic to the rim is in conformity with that of a rainbow and of sunlight dispersed by a prism. But that's not all: Miraculously, the springs edges and the area beyond are perfectly horizontally oriented, so water drains almost equally into all compass directions, which is the icing on the cake in terms of its breathtaking appearance. Another nice feature is the pronounced reflection of the blue color of the water in the steam. Grand Prismatic Spring is no geyser, even boiling as with Excelsior Geyser cannot be observed.

The new observation platform on the hillside southwest of Grand Prismatic Spring, completed in summer of 2017, offers fascinating views down from above on the spring as a whole and on its sections. What you see if you are looking closely seems to be as exotic as a scenery on a planet in a different solar system.

Grand Prismatic Spring, northwest rim:

Grand Prismatic Spring Northwest Rim

Grand Prismatic Spring Northwest Rim
Grand Prismatic Spring hides many secrets, the most exceptional of which may be behind the mesmerizing color pattern. Both colors and their brilliance are not always the same, they vary with the change of weather and of seasons. Microbe communities along the springā€˜s rim, adapted to its weak alkaline conditions (pH 7.0 to 8.3), vary in species and composition depending on water temperature as well as on exposure to sunlight and species-specific nutrients or toxins. The outer brown areas, supplied by already cooled effluent water of 30 °C to 45 °C (86 - 113 °F), feature stratiform mats of brownish-black Calothrix cyanobacteria. These microbes protect themselves against the sun by the dark brown pigment scytonemin.
The lower, 45 °C to 60 °C (113 - 140 °F) warm outflow channels and areas of Grand Prismatic Spring are dominated by long streamers and filamentous mats of orange-tan Phormidium laminosum cyanobacteria. Just as Calothrix they use pigments as sunscreen, but in this case orange to red carotenoids. Phormidium is associated with orange (in winter green) filaments of Chloroflexus aurantiacus, which prefer the same temperature range and apply green bacteriochlorophylls to carry out photosynthesis. Closer to the spring at a temperature range of 52 °C to 74 °C (126 - 165 °F) biofilms of yellow-green Synechococcus cyanobacteria perform oxygenic photosynthesis and fix carbon dioxide. The brightly yellow, but occasionally pink or red colored streamers of Thermus aquaticus prefer even higher temperatures of up to 80 °C (176 °F) at the very edge of the spring until the water gets too deep. This hyperthermophilic bacterium consumes other mircobes and organic matter to grow and sustain life.
In contrast to the sterile blue water in center, whose temperature reaches 87 °C (189 °F) in the depth, the internal edges of Grand Prismatic Spring may also be colonized by microbes, however, this has not yet been confirmed. Parallelling the except size very similar Octopus Spring in White Creek Group, the presence of pale hyperthermophilic bacteria from the group of Aquificales such as Thermocrinis or Hydrogenobacter can be expected.

Grand Prismatic Spring, southeast rim:

Grand Prismatic Spring Southeast Rim

Grand Prismatic Spring Southeast Rim
In August 2014, a Dutch tourist crashed a remote-controlled camera drone into Grand Prismatic Spring, only two months after the US National Park Service had banned all drones from the parks. Although great efforts were made to locate the drone inside the spring by a helicopter as well as by visual observation from the ground, it could neither be recovered nor be detected at all. Experts fear that the drone may release pollutants and harm the sensitive microbe communities of the spring.

Besides Excelsior Geyser the very colorful Opal Pool is the second geyser on location. However, its eruptions are rare, only a few times per year, and years of complete dormancy are also known.

Opal Pool:

Opal Pool Yellowstone

Opal Pool Yellowstone
A little bit off the boardwalk is Turquoise Pool, a quiet hot spring.

Turquoise Pool:

Turquoise Pool Yellowstone

Turquoise Pool Yellowstone

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