Location of the Hot Spot
Basalt flows and cinder cones
at Craters of the Moon National Monument have periodically erupted from the north
end of the Great Rift over the last 15,000 years. The frequency of these eruptions
is about once every 2,000 years and the last eruption was about 2,000 years ago.
Basalt flows in the Blackfoot-Gem Valley lava field blocked and rerouted the Bear
River, forcing it to bend to the south across the Portneuf Range at Oneida Narrows,
and to enter the Bonneville Basin. The additional water from the Bear River was
probably a major contributor to the rise of Lake Bonneville, which culminated
in a catastrophic flood about 14,500 years ago. Glacial erosion of the central
Idaho mountains and the Yellowstone Plateau produced a tremendous volume of silt
that was carried out onto the Snake River Plain by melt-water streams. During
periods of low flow, in the winter and spring, strong winds blew the silt eastward
forming loess deposits. This loess is now the rich soil that grows the "Famous
Potatoes" of Idaho.
Current Location of
the Hot Spot
Cross-section of the
Images courtesy of the U.S.
Forest Service, Department of Agriculture.