West Thumb Geyser Basin, Lower Group - page 3
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.
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.
A few feet northeast of the informally named Skinny Geyser, known for eruptions up to 5 m (15 feet) high, some small springs with sinter rims appear. They are not listed in the RCN database.
The spring farther south exhibits a colorful runoff. Possibly this is North Star Geyser, but I'm not sure about.
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.
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 clear 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. Current temperatures are around 60 °C (140 °F), but during the rare active phases Abyss Pool heats up and shines light blue to deep blue because the yellow microbes die and get replaced by nearly colorless hyperthermophilic microorganisms.
On August 11th, 2022, an alarming sight appeared before the eyes of a park visitor. He spotted a shoe floating sole-up on the surface of Abyss Pool and reported it to the NPS. Five days later, park employees recovered a shoe with remains of an human foot from the spring, perhaps the same that had been seen by the visitor. Until now, the rest of the body could not be detected. According to a park's press release, a DNA analysis revealed that the foot belongs to a 70-year-old man from Los Angeles, who on the morning of 31st of July 2022 got under unsettled circumstances into the spring. In this case, nothing hints to a third-party responsibility.
Before the runoff of Abyss Pool reaches the lake, it flows through King Geyser. That one is a little bit hard to spot from the current boardwalk and it is often obscured by steam. At least until the end of the 1950s an additional loop of the boardwalk, branching off east of Abyss Pool and rejoining the main walk east of Black Pool, ran close to King Geyser on the lakeside. The geyser is very rarely active and reaches eruptions heights of up to 2.5 m (8 feet).
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.
Another muddy hot spring can be found across the highway from the access road to the parking lot.
