Locating Loess Deposits. Looking at dirt may not seem like an exciting way to spend a vacation trip, but the Iowa/Missouri Loess Hills are interesting from the viewpoint of geology, if nothing else. My wife and I were leaving Sioux City, Iowa, after attending a wedding for a relative. Not too far south of Sioux City, on Interstate 29, we saw a sign that read “Loess Hills Scenic Byway.” A stop at a rest area provided some informational literature, and we were on our way to see some loess hills.
Loess (it’s pronounced “luss”) is a type of soil found in most places around the world, but only in China are loess deposits as high (up to 200 feet) as they are along the western border of Iowa and Missouri. The loess deposit area is approximately 15 miles wide and 200 miles long, extending from near Sioux City, Iowa, to St. Joseph, Missouri. Council Bluffs, Iowa, named for the loess bluffs where Native American Indians used to hold councils, is included in the deposit area.
The Formation of Loess. Wikipedia gives some helpful background about the soil. The word “loess” comes ultimately from a Swiss German word which means “loose,” which perfectly describes the loess soil. The hills are the by-products of the end of an ice age. Runoff from melting glaciers created what would become known as the Missouri River. Rocks in the river were ground to fine powdery particles called loess. After the river had done its work and receded to a lower level, the wind took over, blowing the loess particles to the east bank of the river, piling the particles into the hills they are today. At the end of a long process, topsoil was formed, and animal and human life began to inhabit the hills. Archaeological artifacts indicate that humans have lived in the hills for approximately 6000 years.
The Fragile Nature of Loess. Because of its composition, loess erodes easily and can be shifted dramatically by nothing more than the wind. As Wikipedia notes, even well-managed farms of loess soil can lose large amounts of soil each year through erosion.
A map from the rest area showed some road loops that would take us close to deposits of loess. We picked one and began to drive. Looking across the flat Iowa farmland, we saw hills rising in the distance. We pulled off the road near an exposed formation of loess. My wife walked over and got a few handfuls of the soil to take with us. Loess has the deceptive appearance of rock, but under light pressure from the fingers, the “rock” simply crumbles into not much more than dust.
While that may be interesting, what is sobering about the use of the soil in the area we explored is that there are houses sitting on loess. To give some idea of what is at stake, a book about the loess hills, written by Cornelia Mutel, is titled Fragile Giants. When it is remembered that the large deposits of loess were formed primarily by the action of the wind, it is is easy to project the future of houses sitting on top of such deposits, even if, for the time being, there is grass and other vegetation giving at least the appearance of binding the soil together.
Characteristics of Loess. The loess hills exhibit two primary characteristics. First, in most cases, they are composed of very little other than loess soil. There are a few areas where rocks are present, but not generally. Second, if the topsoil is removed from a slope of a hill, the exposed loess will dissolve in the next rain. Even when topsoil is present, the hill can shift, creating what an informational brochure calls “the characteristic ‘cat-step’ ledges” or ridges. The brochure goes on to point out the odd fact that if a loess hill is cut vertically, the exposed wall will stand for years.
The Loess Hills may not be the ideal day trip for everybody, but those interested in the formation of the earth and how different environmental factors produce different soils will find a trip to the loess formations an educational experience. A handful of loess soil may lead to more exciting conversations than a handful of cotton candy from a theme park!
“Iowa’s Loess Hills,” an informational brochure available at Interstate rest areas along the loess deposit area
“Discover Monona County and the beautiful Loess Hills,” an informational brochure also available at rest areas