Iowa's Loess Hills

The story of the Loess Hills of Iowa started more than 25,000 years ago when a large glacier began to retreat from the area. As the glacier melted, water filled the Missouri River valley. When the water level dropped, large amounts of silt were left behind. Much of that silt was swept up by winds and dropped to the east of the Missouri River Valley. Most of the loess piled up within 2–10 miles of the river in a corridor running about 200 miles north to south along the river valley, creating the Loess Hills of Iowa.


The issues facing working landscapes are especially evident in the fragile Loess Hills of western Iowa. Loess is a German word meaning "loose", it's the name of the soil that creates these majestic hills. The Loess Hills span about 200 miles north to south along the Missouri river in Iowa. The depth and concentration of loess deposits found here are only rivaled in certain areas of China. This makes the Loess Hills unique and globally significant. Endangered plants and animals, like the ten-petal blazing star and the ornate box turtle are found on these lands. Lush and rare prairie grasses and flowers are plentiful. But the loess soil is fragile, mainly due to its fine, gritty consistency. This soil is extremely sensitive to water. You may have thought that water first formed these hills, as it did many of the mountains and landforms in this country, but the Loess Hills are special. They were first formed by wind.

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 the 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. But in wintertime water flow was significantly reduced and lots of sand bars and silt material were left exposed on the floor of the valley. Winds from the west were very strong during these times. They would whip through the Missouri valley, pick up the exposed silt material, and deposit it on the east side of the valley.This cycle repeated over thousands of winters until, about 12,000 years ago, the glaciers disappeared and the wind diminished. In their wake, the Loess Hills emerged.

Of course, the erosive power of water eventually played a role. Creeks and rivers fed by rainwater and snowmelt carved most of the distinctive shapes of the Loess Hills that we see today.

Small towns, big cities, farmers, business owners, parks, and preserves combine to make the Loess Hills a huge working landscape. Even though humans have worked this land for hundreds of years, its unique qualities have only come into the limelight in the last thirty years. Awareness of the current threats has also been heightened: threats like erosion, mining, urban sprawl, poor conservation practices, and bad land-use decisions.

Excerpt from "Explore More: Working Landscapes," Iowa PBS, 2003


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