A volcanic explosion 150,000 years ago formed the small caldera known as West Thumb of Yellowstone Lake. Though it occurred many thousand years ago West Thumb is still thermally active with geysers, springs and mud pots. It is the largest geyser basin on the shores of Yellowstone Lake.
There are 2 loop boardwalk trails on West Thumb Geyser Basin. The inner loop trail is 1/4 mile long, the outer loop trail is 1/2 mile long and a small section of it runs next to the Yellowstone Lake.
There are many large and small, prominent and unnamed geysers across the basin. These are some of the features that can be easily spotted from the boardwalk.
Abyss Pool is one of the deepest pools known in Yellowstone. It has crystal clear blue water and cooler temperatures to support microbial growth around its edge. Though it erupted in the past, it has remained calm since the 1990s.
Like Ledge Spring, Collapsing Pool has a ledge around its rim. Part of the ledge has collapsed, for which it was named. The pool has clear blue steaming water.
Bluebell Pool is a steaming pool with crystal clear blue water.
Very much like Fishing Cone, Lakeshore Geyser is also on the shore of Yellowstone Lake and is more submerged under water. Only in the late summer, when the water levels decrease the vent is exposed (pic taken in September). Either way, it is dormant for long periods and any activity is rare.
Lakeside Spring is a blue/green color pool close to Yellowstone Lake shore. The color is a result of thermophiles growing in hot waters of the spring. Run-off from Lakeside Spring flows down into the lake.
Fishing Cone is the most famous geyser at West Thumb. It is located just offshore on Yellowstone Lake and for most of the year it remains submerged by fluctuating water levels. Early fishermen would fish in the lake and promptly cook their catch in the boiling water of the geyser. It had occasional eruptions until the 1920s. It remains dormant since but sputtering from a small side vent occurs every few mins.
Percolating Spring is another calm blue pool which shows minor activity only when there is an energy surge. The activity limits to boiling water about a foot above the surface.
Surging Spring is another blue pool which follows a regular cycle of boiling and overflowing. The surging cycle occurs every 4-5 mins.
Thumb Geyser is also one that shows any activity only during energy surge. It can erupt up to 10 feet high.
Thumb Paint Pots:
One of the fascinating features of West Thumb Geyser Basin. A small area consisting of mud cones and mud pools. The pools are hot and bubbling like a thick soup which can also be heard from the boardwalk.
Ledge Spring is a hot pool named for the ledge that hangs over on one side. It erupts occasionally with more frequent activity occurring in the year 2017. The pool boils and erupts up to 3 feet in roughly 50 min intervals.
Ephedra Spring is located in the inner loop of the basin. It can vary in appearance depending on the water level and temperature in the pool.
Until 1991, Black Pool displayed a deep green-black color which gave this pool its name. Changing temperatures and eruptions killed bacteria responsible for the black color and the pool now remains crystal clear and blue. Although bacteria mats don't exist around its rim anymore, its warm run-off waters have caused mats to form along its flow.
Big Cone is the third geyser sitting on Yellowstone Lake, next to Fishing Cone. There is not much activity going on here except for the constant steaming, which also ceases when the water levels rise and the cone is submerged.
Blue Funnel Spring:
Blue Funnel is one of the colorful pools in West Thumb located in the center of the basin. It is known for its clear striking blue color water. Seems like the water has drained quite a lot and the color is not as striking.
There are many tiny springs across the basin. Among them, Venting Pool is the most prominent one and often shows some weak activity.