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News Release, Kansas Geological Survey, Nov. 1, 1995

Geologist Relates Ancient Faults, Present Landscape

LAWRENCE--The hills and hummocks of the Kansas landscape, even the course of some of its rivers, may have been determined by subtle movements along ancient underground faults, according to a geologist at the Kansas Geological Survey, based at the University of Kansas.

Survey geologist Pieter Berendsen, who has studied the relationship between faulting and the landscape, will present results of his work at the annual meeting of the Geological Society of America in New Orleans on Nov. 7, 1995.

For several years, Berendsen has mapped the midcontinent's faults--underground locations where layers of rock have moved in relation to each other. Many of those faults first moved hundreds of millions of years ago, and probably produced earthquakes at the time.

However, more recent movements along those same faults, or reactivation, may have taken place during the past several million years, says Berendsen. And that may have affected the landscape above the subsurface.

For example, in the Flint Hills of Chase County, Kansas, Berendsen has used data from drilling of oil and gas wells to map underground faults that are part of a well-known fault zone, called the Humboldt Fault Zone, that stretches from northern Kansas to southern Kansas. The Humboldt Fault Zone occasionally produces small earthquakes and geologists say it will continue to produce tremors, though most are too small for people to feel.

Berendsen believes the topography of the ground above those faulted areas may have been directly influenced by small movements in the faults. In an area southwest of Cottonwood Falls, a large block of land has been lifted up by faulting, exposing the surface to erosion and creating a landscape that became hilly as it was dissected by erosion. In other places, blocks of land were downdropped, and thus more protected from erosion, resulting in a flatter landscape.

"These contrasts in topography match up with areas where there has been faulting in the subsurface," said Berendsen. The original faults in the area's sedimentary rocks probably occurred shortly after the rocks were deposited, about 500 million years ago. The reactivation of the faults probably occurred in the past several million years.

Those faults may also have influenced the course of rivers in the state. For example, where blocks of land have been lifted up by faulting, rivers may flow along the edges of those blocks. Parts of the course of the Cottonwood River in Chase County, for example, follows the edge of one of those faulted blocks that Berendsen had identified.

"Knowing the locations of those old faults, and their reactivation, has important ramifications for many engineering projects," said Berendsen. "This includes dams, power plants, waste-disposal sites, and other building projects. By learning where those old faults have been reactivated, we learn more about the best locations for many facilities."

story by Rex Buchanan
for more information, contact Pieter Berendsen (785-864-3965)

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