Elevation: 7,733 ft (2,357 m)
Area: 131.7 sq mi (341 sq km)
Shoreline: 141 mi (227 km)
Width: 14 mi (23 km)
Length: 20 mi (32 km)
Avg depth: about 140 ft (42 m)
Max depth: 410 ft (125 m)
Avg summer temp: 45°F (70°C)
West Thumb Facts
West Thumb is a caldera within a larger caldera.
Active hydrothermal features exist on the lake bottom here and elsewhere in the lake.
West Thumb Geyser Basin overlooks Yellowstone Lake, the largest lake at high elevation in North America. You can best appreciate its vastness in winter when the frozen surface extends as a white sheet for miles. Summer is the season to appreciate the lake's many moods. Here you can enjoy its calm, quiet mornings or witness the wind-whipped whitecaps of afternoon storms. After storms, look for rainbows arching into the wilderness beyond, a land nearly as wild as when Native Americans and explorers experienced it centuries ago.
The surface of the lake hints of what exists below. Surveys of the lake bottom in the 1990s documented hot springs and hydrothermal vents just offshore in West Thumb. Look closely—you may see their swirling patterns in the water.
Framed on the east by the Absaroka Range, the lake may be thought of as the heart of Yellowstone. Its waters are the lifeblood for a large network of plant and animal communities. Trumpeter swans and moose thrive on the aquatic growth in shallow waters along the shore. Trout are drawn to zooplankton living in these waters. Cutthroat trout are food for pelicans, otters, eagles, black and grizzly bears, and other wild life. Unfortunately, this population of cutthroat trout is now threatened by non-native lake trout.
As you walk among the basin's superheated waters, you may wonder if the lake is warmer here than elsewhere. After all, the geyser basin pours an average of 3,100 gallons (11,733 liters) of hot water into the lake every day. But even here, the lake's average summer temperature is 45°F (7°C).
The large circular bay of West Thumb is an excellent example of a volcanic caldera. A powerful volcanic explosion approximately 174,000 years ago caused the earth's crust to collapse, creating the West Thumb caldera. The depression produced by the volcano later filled with water to become this large bay of Yellowstone Lake.
The West Thumb caldera lies within an even greater caldera, the Yellowstone Caldera, which is one of the world's largest and encompasses the central and southern portions of the park. Much of your visit in Yellowstone may be spent within the boundaries of this huge caldera. This larger caldera, and the lava that eventually filled it, shaped much of the present Yellowstone landscape. It resulted from a massive eruption roughly 640,000 years ago. Since that time, numerous lava flows have filled the caldera.
A Bit of History
People have long been drawn to West Thumb. Native Americans favored campsites in this area as they hunted bison in the summer. The Crow people gathered medicinal herbs here. Shoshone and Bannock peoples have stories about the formation of the lake. Early scientific expeditions, which corroborated the tales of colorful hot springs mentioned by mountain men, rested here. Visitors in the late 1890s and early 1900s appreciated a refreshing boat ride to Lake Yellowstone Hotel after several dusty days on rutted roads. The rustic log cabin near the parking lot was the original West Thumb Ranger Station built in 1925; it is one of the few such stations remaining. Now it serves as a summer visitor information station and a winter warming hut.
The colors you see in the pools of West Thumb are created, in part, by thermophiles (heat-loving microorganisms). Generally, green and brown indicate organisms living in cooler water, orange and yellow indicate those living in hotter water. Only a few microorganisms thrive in the springs where the temperature is close to boiling, so we see the clear, blue water. In these hot springs, the water absorbs all wavelengths of light except blue, which the pool reflects.
Hydrothermal features are fragile rarities of nature. Yellowstone preserves the largest collection of hydrothermal features on the planet. You have an unparalleled opportunity to view hot springs, geysers, mudpots, and fumaroles in a natural setting.
Change takes place naturally in a hydrothermal area, but people can disrupt these processes and cause irreparable damage. Rocks, sticks, and other objects thrown into a hydrothermal feature may be permanently cemented in place, choking off water circulation and ending all activity.
For the sake of all who follow, never throw objects into any feature. Stay on established walkways for your safety and to protect fragile formations that have formed over thousands of years.
It is illegal to collect any natural or cultural objects or to remove, deface, or destroy any plant, animal, or mineral in Yellowstone's hydrothermal areas. Bring drinking water; take out all trash.
While viewing or photographing the area, protect your camera, glasses, and binocular lenses from hydrothermal heat and stray.
Toxic gases exist in Yellowstone. Dangerous levels of hydrogen sulfide and carbon dioxide have been measured in some hydrothermal areas. If you feel sick, leave the location immediately.
Help preserve Yellowstone for the future.