The west Thumb Geysir basin is the largest Geysir basin on the bank of the Yellowstone Lakes in the Yellowstone national park. Among the west Thumb Geysir basin also the Potts basin in the north ranks.

The source of heat of the hydrothermalen objects of this area lies with approximately 3000 m depth relatively close of the earth's surface. The basin was formed by an outbreak of the Yellowstone volcano before approximately 125.000-200.000 years. Later the developed Caldera filled with water and expanded so the Yellowstone Lake. The west Thumb basin is about as largely as the Crater Lake in Oregon, however substantially smaller than the Yellowstone Caldera, which developed with the volcanic eruption before 600,000 years in same place. It is thus a Caldera in a larger Caldera.

When the underground magma chamber bulged, developed circular locations of fracture, which let the magma escape. It is to today the source of heat for the west Thumb Geysir basin.

The hydrothermalen objects of this region are not only at the lakeshore, separate spread also under the lake. Into the 1990er years several underwater Geysire were discovered. They can be recognized in the summer as weak curvature in the water, and in the winter as melted holes in the ice. The ice of the Yellowstone Lakes is thick on the average in the winter about 10 cm.

See also

• Upper Geysir basin
• Norris Geysir basin

Related links

• Geological overview of the Grant Village and west Thumb area (English)

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