Paha (landform).html



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A Paha is a hill or ridge, typically formed of sand and capped with loess.¹ The word paha means hill in Dakota Sioux.². The most well known Paha is the paha around which the town of Mount Vernon, Iowa developed.

Origin

An early theory of the origin of the paha hills of Iowa described them as being "composed in part of water-laid sand and silt and in part of ice-moulded till."³

Later, after it came to be understood that loess was wind deposited silt, paha's came to be interpreted as a kind of sand dune. "Their persistent southeasterly trend suggests deposition of the loess by prevailing northwesterly winds, possibly anticyclonic winds blowing from the retreating ice sheet."⁴

Explaining Pahas as a kind of dune does not explain why they are not shaped like other dune forms. The modern explanation is that the shape of Pahas was the result of the permafrost conditions that dominated glacial till plains of the Iowan surface during the last ice age. Permafrost effects controlled both the way this surface eroded and the way loess accumulated on this surface. ⁵

Distribution

There is a well-defined band of pahas between Mount Vernon, Iowa and Martelle, crossed by Iowa Highway 1. The large majority of pahas are in Benton, Linn, Johnson and Jones counties in Iowa. These are on the Iowan surface in north-east Iowa.

Casey's Paha State Preserve in Hickory Hills County Park, Tama County, Iowa preserves the south-east end of a two-mile long (3 Km) paha.

Paha ridges have also been identified on the Kansan surface, generally not far from Iowa,⁶ and in western Illinois and eastern Europe.⁷ Similar ridge forms occur in the arid upwind parts of the Palouse region of Washington.⁸ Outside of the Midwest, several of the above-cited authors use the term greda to refer to features that are indistinguishable from Paha ridges.

References