The West Thumb Geyser Basin at the SW end of Yellowstone Lake contains thermal features, such as this sinter mound, both above and below the lake shore. The West Thumb embayment of Yellowstone Lake is a smaller caldera that formed as a result of an explosive eruption during a period of mainly lava-producing eruptions during the past 150,000 years.

Photo by Lee Siebert, 1994 (Smithsonian Institution).

This image is made available under the Public Domain Dedication CC0 license, but proper attribution is appreciated.

Yellowstone