Loess Hills
From Wikipedia, the free encyclopedia
The Loess Hills are a formation of wind-deposited loess soil in the westernmost part of Iowa and Missouri along the Missouri River.
Contents |
[edit] Geology
The Loess Hills are generally located from between 1 and 15 miles to the east of the Missouri River channel. These hills are the
During the Ice Age, glaciers advanced into the middle of North America, grinding underlying rock into dust-like "glacial flour". As temperatures warmed, the glaciers retreated and vast amounts of meltwater and sediment flooded the Missouri River valley. The sediment was deposited on the flood plain, creating huge mud flats. When meltwaters receded, these mud flats were exposed. As they dried, the fine-grained silt was picked up by strong prevailing westerly winds. Huge dust clouds were moved and redeposited over broad areas. The heavier, coarser silt was deposited close to the Missouri River flood plain, forming vast dune fields. The dune fields were eventually stabilized by grass. Due to the erosive nature of loess soil and its ability to stand in vertical columns when dry, the stabilized dunes were eroded into the corrugated, sharply-dissected bluffs we see today.
The dominant features of this landscape are "peak and saddle" topography, "razor ridges" (narrow ridges, often less than ten feet wide, which fall off at near ninety-degree angles on either side for 60 feet or more), and "cat-step" terraces (caused by the constant slumping and vertical sheering of the loess soil). The soil has a characteristic yellow hue and is generally broken down into several units based on the period of deposition (Loveland, Pisgah, Peoria). Loess is known locally as "sugar clay" because it can be extremely hard when dry, but when wet, loses all cohesion. The Loess Hills of Iowa are remarkable for the depth of the drift layer, often more than ninety feet deep. The only comparable deposits of loess to such an extent are located in China.[citation needed]
[edit] Geography
Today, these hills stretch from Westfield, Iowa in the north to Mound City, Missouri in the south. Loess topography can be found at various points in extreme eastern portions of Nebraska and Kansas along the Missouri River Valley, particularly near the Nebraska cities of Brownville, Rulo , Plattsmouth , Fort Calhoun and Ponca.
[edit] Biology
The Loess Hills have abundant oak-hickory hardwood forests and some of the last remaining stands of prairie grass in the region. The invasion of prairie and oak savanna areas by woodland species such as red cedar (not native to the Hills) is threatening the stability of the fragile soils, as well as diminishing the native ecosystems found there. The areas of native prairie are comprised of big bluestem and little bluestem, Indian grass, sideoats grama and forbs such as yucca, pasque flower and lead plant (false indigo). Many of the prairie species found in the Loess Hills are outside of their normal range of distribution, with plants like spiny-leafed yucca and prickly pear cactus being more common further west, in the Sand Hills of central Nebraska. In 1984, a previously undiscovered fern, the Prairie Moonwart, was discovered in the Hills and is thought to be endemic to the Hills. Common fauna of the modern Loess Hills include white-tail deer, coyote, wild turkey, badger, bobcat, red and gray fox, ringneck pheasant, bobwhite, and red-tailed hawk, some of which were introduced or encouraged by Euro-American settlers. Woodland species are also on the rise in the Loess Hills as the suppression of fire has led to an increase in habitat for forest-dwelling species. Fauna more typical of the pre-settlement Loess Hills, such as the prairie rattlesnake, great plains skink, plains pocket mouse, ornate box turtle and spadefoot toad, are becoming rare and even endangered due to habitat fragmentation as a result of increased development and suppression of fire in prairie remnants and oak savannas. Species such as bobcat have been rebounding, and mountain lions have been recorded in Southwest Iowa in the last decade. Historically, fauna also included American bison, prairie chicken, mule deer, elk, and gray wolf; these were extirpated by the late-nineteenth century.
The Missouri River valley had historically been a major migration corridor for birds, however, the channelization of the river and destruction of wetlands has led to a marked decline. However, the corridor still boasts one of the best areas to view raptor migrations on the continent. As air masses move off of the Great Plains, they sink into the Missouri River valley. The prevailing winds across the floodplain then hit the sharp rise of the Loess Hills, creating thermal updrafts that raptors use to make their way to and from breeding grounds. Raptors can often be viewed forming "kettles" where many birds will create a funnel-like formation as they utilize the same thermal. Typical species found during the months from September to December include red-tailed hawk, sharp-shinned hawk, peregrine falcon, ferruginous hawk, Swainson's hawk, Cooper's Hawk, Osprey, Northern Harrier, American Kestrel, and Bald Eagle. In all, 20 species of raptor have been identified in a single season since Hitchcock Nature Center HawkWatch started, with a record count of 16,000 birds in one season in 2005.
[edit] Recreation and public lands
The Loess Hills Scenic Byway affords many scenic views as it twists through the range from north to south, starting in Westfield, Iowa and ending in Hamburg. While much of the landscape is held in private ownership, thousands of acres of public land exist in state and county parks, wildlife areas and preserves. The Nature Conservancy also owns several preserve areas in the Hills which are open to the public, including Broken Kettle Preserve - the largest contiguous tract of native prairie left in Iowa and home to the last remaining known population of prairie rattlesnake in Iowa. The Loess Hils State Forest is located in west-central Iowa in Harrison and Monona counties. It is comprised of 4 units totaling 10,600 acres, and offers hiking, backpacking, picnicking, and fishing opportunities. Preparation Canyon State Park, located in the middle of the range, near Pisgah, is a less developed park in the middle of the Loess Hills State Forest. Backpacking trails lead to hike-in campsites. Two major state parks anchor the north and south end of the range - Waubonsie in the south and Stone in the north, both offer camping and a variety of other amenities. Hitchcock Nature Center is located about 20 miles north of Omaha and features a lodge with raptor viewing platform and observation tower, from which one has striking views of the Hills, Missouri River Valley and the skyline of downtown Omaha. Hike-in camping is also available at this location.
Two National Natural Landmarks are located in the Loess Hills. The Little Sioux/Smith Lake Site contains 2,980 acres and is perhaps the best example of the unique topography produced by large deposits of loess soil. The 7,440 acre Turin Site of the Loess Hills National Natural Landmark is located just outside of Turin and also contains the Turin Man prehistoric arhceological site.
[edit] Human history
The Loess Hills have a rich archaeological heritage. The hills around Glenwood, in Mills County, were inhabitated by the Glenwood Culture, an eastern extension of the Nebraska Phase of the Woodland period. The Glenwood Culture lived in the area from roughly 900 A.D. to 1300 A.D. and built hundreds of earth lodges in the region, farming the rich valley bottoms and cultivating native plants from the surrounding hills. An earth lodge replica has been reconstructed in Glenwood Lake Park, and the Mills County Museum, also located at the park, houses an excellent collection of artifacts collected by renowned amateur archeologist Paul Rowe.
[edit] Other loess landscapes
Loess soil also forms the Arikaree Breaks in northwest Kansas, and the Mississippi-Yazoo "Bluff Hills" near Vicksburg, Mississippi. A large region of Nebraska to the south and east of the Sand Hills is covered with loess. Deep loess deposits are also found in the Rhine River valley in Germany. The word loess is derived from the German for "loose or crumbly."
[edit] External links
- Loess Hills Scenic Byway
- Loess HIlls Western Iowa
- Geology USGS
- Fragile Giants
- Loess Hills State Forest
- Sen. Charles Grassley on the Loess Hills
