How the Loess Hills Were Formed

Twelve to thirty thousand years ago glaciers were moving and melting over parts of the Iowa landscape and the states to the north. Due to changes in temperature, the front of the glaciers would melt in the summer and huge amounts of meltwater would flow down the Missouri River valley.
In the wintertime, the glaciers stopped melting. The flow of water into the rivers slowed down significantly. This exposed sandbars and silt material on the floor of the valley.

Wind Creates Hills

Winds from the west were very strong during these times and they would whip through the Missouri River valley, pick up the exposed silt material and deposit it on the east side of the valley. This cycle was repeated over thousands of winters until about twelve thousand years ago.
The glaciers disappeared and the wind diminished. The Loess Hills of Iowa remained. As time marched on, water carved the hills by eroding the silt. Creeks and rivers, fed by rainwater and snowmelt, rushed down the slopes, creating most of the distinctive shapes of the Loess Hills that we see today.

Explore More: Working Landscapes
Copyright 2004, Iowa Public Television
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