Volcanic Springs

Geysers, Hot Springs,
Mud Pots, and Fumaroles

West Thumb Geyser Basin, Lower Group - page 3

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On the way back upslope the trail passes Black Pool. Up until 1991 it really exhibited a dark green, near black color. But then an energy surge let the temperature rise and the spring underwent a series of boiling eruptions. The heat killed the thermophilic bacteria, which had been responsible for the dark color, and Black Pool became transparent blue as it is known today.

Black Pool:

Black Pool Yellowstone

Black Pool Yellowstone
The slope southwest of Black Pool is home of some small springs, of which some are geysers. However, the vent of Skinny Geyser, the one closest to the boardwalk and to Black Pool, is unimpressive and hard to detect from the trail.

Springs on the slope southwest of Black Pool:

Springs southwest of Black Pool Yellowstone

In the vicinity of the informally named Skinny Geyser, known for eruptions up to 5 m (15 feet) high, some small springs with geyserite rims appear. They are not listed in the RCN database.

Unnamed springs west of Black Pool:

Unnamed spring west of Black Pool West Thumb Basin Yellowstone


Unnamed spring west of Black Pool West Thumb Basin Yellowstone

The spring farther south exhibits a colorful runoff. Possibly this is North Star Geyser, but I'm not sure about.

Unnamed spring southwest of Black Pool:

Unnamed spring southwest of Black Pool West Thumb Basin Yellowstone

Hillside Geyser is located a little bit remote 30 m (100 feet) upslope of Black Pool. There are only a few reports about eruptions up to 100 feet tall. The last one occured in 2005.

Hillside Geyser:

Hillside Geyser West Thumb Basin Yellowstone

Hillside Geyser Yellowstone
Far more eye-catching compared to those small springs is Abyss Pool. Even if geyser activity with eruptions up to 100 feet is known, Abyss Pool usually is a quiet pool. It is also one of the deepest blue pools of Yellowstone. The exceptional rich green color is a result of the combination of the yellow, microbe-populated lining and the blue diffraction color of pure water. Living thermophilic microbes indicate that Abyss Pool currently is not as hot as it was during its active phases.

Abyss Pool:

Abyss Pool Yellowstone

Abyss Pool

Abyss Pool and its runoff:

Abyss Pool Yellowstone

Abyss Pool
Before the runoff of Abyss Pool reaches the lake, it flows through King Geyser. That one is a little bit hard to spot and often obscured by steam. King Geyser is very rarely active and reaches eruptions heights of up to 2.5 m (8 feet).

King Geyser:

King Geyser West Thumb Basin Yellowstone

King Geyser Yellowstone
When you return to West Thumb parking lot, there is also the chance to observe further thermal features. The muddy hot spring WTLGNN031 is located at the western corner of the parking area.

Muddy hot spring WTLGNN031 at West Thumb Parking Lot:

Muddy hot spring WTLGNN031 Yellowstone

Another muddy hot spring can be found across the highway from the access road to the parking lot.

Muddy hot spring WTLGNN032 at West Thumb Parking Lot:

Muddy hot spring WTLGNN032 Yellowstone

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