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Earthquakes, glaciers, volcanic activity, unique water systems, and pockets of hydrogen sulfide gas have all played a role in the unique geological history comprising the Lake, Bridge Bay, and Fishing Bridge Areas.

Yellowstone Lake
Yellowstone is alive with volcanic activity, and researchers now look to Yellowstone Lake as proof of this conclusion. 600,000 years ago, major eruptions occurred at the volcanic vents of Mallard Lake Dome near Old Faithful and Sour Creek Dome near Fishing Bridge. As a result of these eruptions that measured 1,000 times the magnitude of the 1980 Mt. St. Helens explosion, Yellowstone Lake’s 136-square mile lakebed formed.

Although no major explosion has since occurred, the Mallard Lake Dome and Sour Creek Dome remain active. Known as resurgent domes, these volcanic vents continue to rise and fall with each passing year. As a result of Sour Creek’s activity, Yellowstone Lake is tilting right beneath researchers’ eyes. The lake now angles towards the south, flooding forests in the southern arm and exposing new beaches on the lake’s northern shoreline. Researchers believe it is only a matter of time before Yellowstone erupts again and clouds the continent in a sea of ash.

Hayden Valley
Now a marsh covered with abundant plant life, the Hayden Valley was once hidden beneath the deep waters of Yellowstone Lake. When the water retreated, it left behind fine lake sediment deposits soon buried under glacial till from glacier activity dating back nearly 13,000 years. As a result of these ancient deposits, water is unable to penetrate through the ground layers of Hayden Valley, which results in the valley’s marshy landscape.   

Mud Volcano

A highly unique, eerily captivating site, the Mud Volcano Area’s activity is easily explained through the Earth’s natural geological processes. A unique water system where the ground water boils away faster than it settles leaves Mud Volcano nearly devoid of water. As a result, numerous steam vents form that allow hydrogen sulfide gas vapors to escape from deep within the Earth’s surface. These vapors dissolve the area’s rock into clay and also combine with water and bacteria to form highly acidic pools. When these sulphur pools, carbon dioxide, steam, and clay join together, visitors are treated to a spectacular display of bubbling mudpots.

Since the area is highly acidic and soil temperatures average a consistent 200 degrees Fahrenheit, vegetation is unable to survive. “The Cooking Hillside” is a famous example of this characteristic, and shallow earthquakes further spread the range of these high temperatures, acid, and sulphuric gas by forming new fractures in the area’s fragile crust.

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Hayden Valley
Hayden Valley, NPS Photo

Geological Overview of the Lake, Lake Bridge
and Fishing Bridge Areas