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Ancient volcanic activity, blue-green thermal pools, and underwater thermal disturbances join together to provide a unique geological look into Yellowstone’s West Thumb and Grant Village Areas.

West Thumb Geyser Basin
Regarded as the largest geyser area on Yellowstone Lake’s shoreline, the West Thumb Geyser Basin features a heat source located just 10,000 feet below the surface. The nearly too-close-for-comfort heat source formed when an underground magma chamber cracked, spewing the magma towards the surface through tiny ring fractures. 

West Thumb Thermal Features
Most of Yellowstone’s thermal features are readily apparent to the naked eye on the park’s surface. West Thumb, however, is unique in that many of the area’s features are actually active underneath Yellowstone Lake’s placid exterior. Researchers discovered numerous underwater geysers during the 1990s. Evidence of this activity is apparent as a slight bulge on the water’s surface during summer and as melted holes in the lake’s icy cloak during winter.

West Thumb Yellowstone Lake
A massive volcanic explosion approximately 150,000 years ago resulted in a large caldera (a collapsed volcano). When water filled the caldera and flowed over into the previously existent Yellowstone Lake, the West Thumb of Yellowstone Lake was born. The West Thumb crater is comparable in size to its famous caldera counterpart at Oregon’s Crater Lake.

Geological Overview of the Grant Village and
West Thumb Areas