MIDWAY GEYSER BASIN (YELLOWSTONE HOTSPOT) HYDROTHERMAL FEATURES

Midway Gesyer Basin (above & below), view from atop Midway Bluff in August 2011.

Above: looking ~SSW toward the Firehole River flowing north through the Midway Geyser Basin. The Rabbit Creek Group is just to the left of the southern end of the tree-covered hill at center. The Flood Group is at the extreme left edge. The southernmost Excelsior Group is the geyserite (siliceous sinter) platform at right.

Below: looking ~WSW toward the Excelsior Group.

Grand Prismatic Spring (above & below), Excelsior Group, northern Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011.

Grand Prismatic Spring is, by far, the most beautiful thing I’ve ever seen. This rainbow-colored hot spring is best appreciated from the boardwalk along the northeastern edge of the pool (see below photos) and from atop Midway Bluff (see above photo), a hill on the eastern side of the highway next to the Firehole River and from “7622 Hill” on the southeastern side of Fairy Falls Trail/Fountain Freight Road.

The deep blue color at the center of the pool is the result of very hot water having abundant, suspended, <0.5 micron-sized, colloidal silica particles. The yellow, orangish, reddish, and brownish areas are mats of extremophile bacteria (e.g., Phormidium, Synechococcus, Calothrix). The greenish areas are the effect of “blue water” mixing with the light reflecting from the yellowish bacterial mats.

Grand Prismatic Spring is the largest hot spring in the world. It does not erupt as a geyser.

Above: view to the ~WSW from atop Midway Bluff.

Below: views from the Midway Geyser Basin boardwalk.

Grand Prismatic Spring

Grand Prismatic Spring (above & below) - view to the ~NW from the Flood Group area.

Above: whitish-colored steam rising from Grand Prismatic Spring, photographed without a polarizing filter.

Below: multicolored steam rising from Grand Prismatic Spring, photographed with a polarizing filter.

Grand Prismatic Spring - multicolored steam rising from the hot spring.

Filamentous extremophile bacteria - samples of microbial mats from Grand Prismatic Spring show the presence of Phormidium (above left) and Calothrix (above right), both photosynthesizing cyanobacteria. Photos from National Park Service trailside signage.

Excelsior Geyser (above & below), Excelsior Group, northern Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011.

Above: looking ~W from atop Midway Bluff - the large, steaming, deep blue-colored pool lined by geyserite cliffs on its left side is Excelsior Geyser.

Very large, and even explosive, eruptions occurred at Excelsior Geyser in the 1880s, during which the present, large, cliff-lined crater was formed. 1880s eruptions reached as high as 300 feet. Apart from activity in 1946, 1985, and 2000, Excelsior Geyser has merely been a massively overflowing hot spring. Its overflow consists of almost six million gallons of water per day. Thick steam frequently obscures much of the crater and the pool.

Excelsior Geyser (above & below)

Above: view to the ~NW from the Flood Group area.

Below: views from the Midway Geyser Basin boardwalk.

Excelsior Geyser (looking ~ENE)

Excelsior Geyser (looking ~N)

Excelsior Geyser (looking ~NW) - the two rounded hills in the left background are Twin Buttes, composed of Pleistocene-aged, glacially-deposited sandstones and conglomerates. Twin Buttes are on the northwestern margin of an old, moderately large, hydrothermal explosion crater.

Excelsior Geyser (looking ~NE)

Excelsior Geyser (looking ~E) - the hill in the background is Midway Bluff. Fantastic views of Midway Geyser Basin, and especially Grand Prismatic Spring, are available from atop the bluff, accessible via two trails leading up from the road.

Excelsior Geyser (looking ~ESE) - extremophile bacterial mats along the hot spring’s runoff channel (northern margin of Excelsior Geyser’s pool).

Excelsior Geyser (looking ~SE) - extremophile bacterial mats along Excelsior Geyser’s runoff channels. Several thousands of gallons of hot water drains directly into the Firehole River every minute.

Opal Pool (above & below), Excelsior Group, northern Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011. The two rounded hills in the distance are Twin Buttes, composed of Pleistocene, glacially-deposited sandstones and conglomerates rimming an old hydroexplosion crater. Opal Pool rarely erupts as a geyser, perhaps up to 80 feet high.

Turquoise Pool (above & below), Excelsior Group, northern Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011. Turquoise Pool does not have geyser eruptions.

Above: looking ~E from atop Midway Bluff.

Below: looking ~NNW.

Indigo Spring (above & below), Excelsior Group, northern Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011 (looking ~WSW from atop Midway Bluff).

Indigo Spring does not have geyser eruptions.

Indigo Spring - runoff channels along the western banks of the Firehole River. The yellows, oranges, and browns are extremophile bacterial mats that thrive in hot water runoff.

Circle Pool, Flood Group, central Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011 (looking ~SW). Circle Pool does not have geyser eruptions, although a couple geysers do occur in the immediately vicinity.

Flood Geyser, Flood Group, central Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011 (looking ~SW). Flood Geyser has frequent eruptions up to 25 feet high.

West Flood Geyser, Flood Group, central Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011 (looking ~SW). This feature’s behavior varies - it has been a hot spring pool, an overflowing hot spring, and a sometimes-frequently erupting geyser.

Info. mostly synthesized from:

Bryan, T.S. 2008. The Geysers of Yellowstone, Fourth Edition. Boulder, Colorado. University Press of Colorado. 462 pp.

Fritz, W.J. 1985. Roadside Geology of the Yellowstone Country. Missoula, Montana. Mountain Press Publishing Company. 149 pp.

Muffler, L.J.P., D.E. White & A.H. Truesdell. 1971. Hydrothermal explosion craters in Yellowstone National Park. Geological Society of America Bulletin 82: 723-740.

National Park Service trailside signage.

Ohsawa et al. 2000. Geothermal blue water colored by colloidal silica. Proceedings of the World Geothermal Congress, 2000, Kyushu-Tohoku, Japan, May 28-June 10, 2000: 663-668.

Schreier, C. 1987. A Field Guide to Yellowstone’s Geysers, Hot Springs and Fumaroles. Moose, Wyoming. Homestead Publishing. 96 pp.

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