Overview

Hype:

Midway Geyser Basin is home to two of the largest geothermal features in Yellowstone. The Grand Prismatic Spring is the largest hot spring in the US, and Exelsior Geyser Crater discharges over 4,000 gallons per minute.

Trail Condition: Class 0 (Trail is paved. No elevation gain.)

Time: 20-30 minutes

Length: 0.8 miles round trip

Fees: Entrance fee

Recommended Ages:

	0-3
	4-11
	12-19
	20-49
	50-69
	70+

Recommended Months to Visit:

Jan

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Apr

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Jun

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Aug

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Getting There

Navigate to 44.527836, -110.835800.

Midway Geyser Basin is located about half-way between the Madison and Old Faithful regions of Yellowstone National Park. From the parking lot, take the trail south and cross the Firehole River.

Route

Midway Geyser Basin is much smaller than the other basins found alongside the Firehole River. Despite its small size, it contains two large features: the 200-by-300-foot-wide Excelsior Geyser which pours over 4,000 gallons per minute into the Firehole River and the 370-foot-wide and 121-foot-deep Grand Prismatic Spring which is the largest hot spring in Yellowstone.

You will see several streams of steaming water pouring from the terrace above into the Firehole River.

Take the right fork and proceed to Turquoise Pool, which will be on your right. The 1878 Hayden Expedition named this pool for its milky, white bottom and gem-like, blue-colored water. Suspended mineral particles in the water also add an opalescent iridescence. Turquoise has no apparent overflow channel; instead water drains through seepage. There is an underground connection with Excelsior Geyser. When Excelsior was active, Turquoise lowered nearly ten feet and took nearly a year to recover. In June and July, purple fringed gentians are common and bloom on the barren ground surrounding this pool.

Further to the west is Opal Pool. Opal Pool is a hot spring in the Midway Geyser Basin of Yellowstone National Park. Opal Pool usually has a temperature of approximately 132 °F. Though usually active as a hot spring, Opal Pool is considered a fountain-type geyser.

The first recorded eruption of Opal Pool was in 1947, recurring in 1949, 1952 and 1953, then ceasing. Eruptions resumed in 1979, happening at least once in most following years. Eruption heights are typically under 30 feet in height, but some eruptions have been seen with heights of 70 to 80 feet. Eruptions occur suddenly following visible convection in the pool but are unpredictable. The eruption consists of one, huge, burst that throws water 20-80 feet high, making Opal Pool the largest active geyser at Midway Geyser Basin. Much smaller splashes seconds apart stretch the total duration to about 1 minute. Sometime in 2005 Opal completely drained, but it refilled as a beautiful green pool in 2008.

Grand Prismatic Spring is the largest hot spring in Yellowstone and is considered to be the third largest hot spring in the world. New Zealand has the two largest springs. Grand Prismatic sits upon a wide, spreading mound where water flows evenly on all sides forming a series of small, stair-step terraces. The Hayden Expedition in 1871 named this spring because of its beautiful coloration, and artist Thomas Moran made water-color sketches depicting its rainbow-like colors. The sketches seemed exaggerations, and geologist A.C. Peale returned in 1878 to verify the colors. The colors begin with a deep blue center followed by pale blue. Green algae forms beyond the shallow edge. Outside the scalloped rim a band of yellow fades into orange. Red then marks the outer border. Steam often shrouds the spring which reflects the brilliant colors. Grand Prismatic discharges an estimated 560 gallons per minute, has a temperature of 147-188°F, and has dimensions of 250x380 feet.

Grand Prismatic Spring can also be seen from atop the hill immediately to the southwest. To get to the hill, drive 1.3 miles south and park at the trailhead to Fairy Falls. Walk north along the foot trail for about 0.6 miles. There will be several small trails criss-crossing up the hill. Pick your favorite one, and have fun. Don't worry, the ranger told us it was OK to leave the main trail.

Excelsior Geyser Crater

Excelsior Geyser was once the largest geyser in the world. However, the last known major eruptions occurred during the 1880s, when there were numerous eruptions up to 300 feet. The violent eruptions of the 1880s may have caused damage to the siliceous sinter lining, allowing gas leakage and the loss of thermal energy. No observed eruptions were known until 1985 when it erupted for two days. However, it only obtained a height of 20-80 feet. Since its eruptive activity in the 1880s, Excelsior is now a productive thermal spring, presently discharging 4050 gallons per minute. Numerous vents boil and churn the water within the crater, covering it in a dense layer of steam. The temperature is 199°F and the dimensions are 276x328 feet.

Maps

Closest City or Region: Yellowstone National Park, Wyoming

Coordinates: 44.527836, -110.835800

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July 11, 2011 Trip Report

By Jeremy Dye

Trip Members

Jeremy Dye, Tara Dye, Savannah Dye, Greg Dye, Laura Dye, Zac Dye, Bryce Ball,

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