Skip to Content

Landscape Features of Iowa

 

The following information is based on the book Landforms of Iowa, by Jean C. Prior, published by the University of Iowa Press, Iowa City, in 1991. The book was designed and illustrated by Patricia J. Lohmann.”

 

The topographic features seen on the following pages illustrate the range of picturesque diversity that is present across our state. In addition to their beauty, each of these landscape views reflects some aspect of Iowa’s geologic history. Understanding the geologic setting of various types of terrain is essential for citizens concerned with farming, urban expansion, recreation, excavation of mineral resources, pumping of groundwater supplies, landfilling of waste materials, and other environmental and natural resource issues. Also, it is useful to think about these landscapes in terms of their influence on the distribution of native plant and animal habitats, on various soil types, on the potential for archaeological remains, and on patterns of historic settlement. Learning more about the features of Iowa’s landscape increases our understanding and appreciation of the views around us and the ground beneath our feet.

 

Landforms of Iowa, 1991

Des Moines Lobe: The icy grip of continental glaciers was one of the  most significant geologic processes to affect the Iowa landscape. Most of the deposits underlying today’s land surface are composed of materials known as drift that were moved here by glaciers. The arrival of these glaciers in the state began over two million years ago, and numerous reappearances are recorded in the deposits they left behind. For all of this massive effort, however, only the landscapes of north~central Iowa still display the actual shapes that resulted directly from glacial action. This region, known as the Des Moines Lobe, is the part of the state last touched by the huge sheets of frozen water that invaded Iowa in the past. This last glacial episode occurred only 12,000 to 14,000 years ago.

For more information on the Des Moines Lobe:  Click Here!

 

 

Landforms of Iowa, 1991

Southern Iowa Drift Plain: The topography of the Southern Iowa Drift Plain is perhaps most representative of “typical” Iowa landscapes. The Southern Iowa Drift Plain is certainly the largest of Iowa’s landform regions, and it is the primary region travelers on Interstate 80 will see. Noted Iowa artist Grant Wood emphasized the steeply rolling character of this landscape in many of his stylized paintings, especially Young Corn and Fall Plowing. The landforms of this region, like those of the Des Moines Lobe, are composed primarily of glacial drift, but the massive ice sheets that carried material into this part of Iowa were older by hundreds of thousands of years than those that occupied the north-central area of the state. It is this geological generation gap that makes all the difference in the appearance between these two regions.

Features typical of a freshly glaciated landscape have been obliterated by time. Gone are the moraines, kames, kettles, bogs, and lakes-all those distinctive visual clues to recent contact with glacial ice. The only remaining evidence to verify passage of these earlier ice sheets is the ten to hundreds of feet of glacial drift covering the bedrock surface. Instead of poorly drained, low-relief landscapes, streams have had time to establish well connected drainage systems and to carve deeply into the land surface. Hillslopes, especially those higher in the drainage network, often display a texture of finely etched rills which give a distinct ribbed or furrowed appearance to the terrain. These rills give way to ravines, then to creeks that flow part of the year, and eventually to perennial streams and rivers in major valleys. Patterned like the branching veins in a leaf, this dendritic network has drained the postglacial wetlands, erased the ice-contact landforms, and through time has reshaped these old glacial plains into the deeply creased landscapes so familiar in this region today.

For more information on the Southern Iowa Drift Plain:  Click Here!

 

Landforms of Iowa, 1991

Loess Hills: Irregularities in the landscape always catch the eye. These differences in elevation are described as the land’s relief, a trait that accounts for much of a visitor’s first impression of a new place. For visitors to western Iowa’s Loess Hills, the scenic relief makes a lasting impression.

The irregular Loess Hills form one of the state’s most distinctive landscapes. They extend in a narrow band that borders the full length of the Missouri River valley in western Iowa. In the heart of the deep-loess landscapes, usually within two to ten miles of the Missouri Valley, the topography is sharp-featured, with alternating peaks and saddles that dip and climb along narrow, crooked ridge crests. Numerous shorter sidespurs branch off the main ridges, and the steeper slopes of both are often horizontally scored with a series of stair-like steps. A dense network of drainageways forming closed-in hollows, narrow ravines, and steep-sided gullies contributes to the intricately carved terrain.

The western boundary of this region is very abrupt as distinct and well defined as a coastline. The bluffs of steeply pitched, prairie-covered ridges and wooded back-slopes stand boldly apart from the lower, flat-lying cultivated fields of the Missouri River valley floor. Some of the most scenic vistas in Iowa appear from ridgetop summits that overlook the boundary between these two contrasting regions. The eastern boundary of the Loess Hills is not easily defined, as the hills merge gradually with the more rolling landscapes of the Southern Iowa Drift Plain. Three state parks, Stone, Preparation Canyon, and Waubonsie, offer good access to the typical landscapes of the Loess Hills.

For more information on the Loess Hills: Click Here!

 

Landforms of Iowa, 1991

Iowan Surface: Sweeping, outstretched landscapes span a large area of the northeastern quarter of Iowa. This relaxed, open topographic style is free of the strong expressions of glacier surges, silt-laden winds, or erosional sculpture that identify the Des Moines Lobe, the Loess Hills, and the Southern Iowa Drift Plain. Part of the individuality of this particular landform region lies in its topographic restraint and subtle land shapes. The tendency not to draw attention to itself also suggests that the region’s landscape features and deposits do not offer an easily recognized geological explanation for their appearance. In fact, the region was a focus of much scientific controversy until new research methods and the concept of stepped erosion surfaces were used in the 1960’s to challenge the generally accepted existence of a separate sheet of Wisconsinan glacial drift in this area.

The physical characteristics of this landform region, identified now as the Iowan Surface, contain numerous clues to an elusive chapter of Iowa’s glacial history. The land surface usually appears slightly inclined to gently rolling with long slopes, low relief, and open views to the horizon. This contrasts sharply with the restricted lines of sight noted within the more billowy, steeply rolling landscapes of the Southern Iowa Drift Plain. Like southern Iowa, however, the hillslopes of the Iowan Surface can be described as having multi-leveled or stepped surfaces. These levels, though subdued, occur in a gradual progression from the major stream valleys outward toward the low crests that mark their drainage divides. It is difficult to pick out a clearly defined valley edge; more often the eye sees only a series of long slopes merging almost imperceptibly with a gentle rise to the next watershed divide. Drainage networks are well established, though stream gradients usually are low and some scattered areas of poor drainage and original wetlands occur. The low-relief landscapes offer very few exposures of their internal composition.

For more information on the Iowa Surface:  Click Here!

 

Landforms of Iowa, 1991

Northwest Iowa Plains: The gently rolling landscapes  of the Northwest Iowa Plains are reminiscent of the low, uniform relief seen on the Iowan Surface. A well-established branching network of streams reaches out over all of northwestern Iowa, providing effective drainage and a uniformly creased land surface. Most of the valleys are wide swales that merge gradually with long, even slopes up to broad, gently rounded interstream divides. This uniform density of stream drainage is important in unifying a region where both Pre-Illinoian and Wisconsinan glacial deposits occur at the land surface.

The uplands in the western half of this region are underlain by Pre-Illinoian glacial tills that have been erosionally stripped of their paleosols. In the eastern half of the region, however, these tills are covered by younger glacial deposits. This sheet of glacial drift, mapped as the Sheldon Creek Formation, links the Northwest Iowa Plains to the Wisconsinan glacial advances displayed so vividly in the landscapes of the Des Moines Lobe to the east. The Sheldon Creek drift is also Wisconsinan in age but was deposited during an earlier glacial episode. Radiocarbon dates place the age of this older ice advance at about 20,000 to 30,000 years ago or 6,000 to 16,000 years earlier than the Des Moines Lobe advance. Deposits of the Sheldon Creek Formation continue eastward beneath the Des Moines Lobe, extending at least as far as western Franklin County where they appear in a quarry near Dows along the Iowa River. They also have been found just above water level in the deeply entrenched valley of Brushy Creek in eastern Webster County. The glacial advance(s) that deposited the Sheldon Creek drift took place just before Wisconsinan climates were at their coldest and just before massive loess deposition and intense erosional activity spread across Iowa’s ice-free, tundra-vegetated landscapes.

For more information on the Northwest Iowa Plains: Click Here!

 

Landforms of Iowa, 1991

Paleozoic Plateau: If Iowa’s landscape had to be divided into only two regions, one would be northeastern Iowa and the other would include everything else. The rugged, deeply carved terrain seen in the Paleozoic Plateau is so unlike the remainder of the state that the contrast is unmistakable, even to a casual observer. The most striking differences include abundant rock outcroppings, a near absence of glacial deposits, many deep, narrow valleys containing cool, fast-flowing streams, and more woodlands. This spectacular high-relief landscape is the result of erosion through rock strata of Paleozoic age. The bedrock dominated terrain shelters unusually diverse flora and fauna , including some species normally found in cooler, more northern climates. Samuel Calvin, one of Iowa’s best known nineteenth century geologists, spoke of these unexpectedly scenic landscapes as the “Switzerland of Iowa.”

The key to this refreshing difference in appearance is the widespread occurrence of shallow Paleozoic-age sedimentary bedrock. In no other region of the state is bedrock in such complete control of the shape of the land surface. The Paleozoic strata include fossiliferous rocks of Cambrian, Ordovician, Silurian, and Devonian age which originated as sediments accumulating on sea floors and along coastal margins of tropical marine environments that existed here between 300 and 550 million years ago. In the course of geologic time, these deposits hardened into brittle rock strata which were later deformed and fractured by crustal movements within the Earth. A widespread series of vertical cracks now extend through these rocks; some of these weakened planes are parallel to each other, others are oriented at nearly right angles. These features, called joints, are responsible for the blocky shapes and sheer faces commonly seen along rock bluffs and roadcuts. Their location also controls the abrupt turns noticed along many stream courses and valley segments throughout the region.

For more information on the Paleozoic Plateau: Click Here!

 

Landforms of Iowa, 1991

Alluvial Plains: Water in motion is one of those timeless processes in nature that hold our gaze and set our thoughts free. For landlocked Iowans, far removed from the rhythmic sight and sound of ocean surf, the strong silent flow of a large river has its own soothing and enduring attraction. Iowa also has hundreds of small brooks and creeks that can be crossed with a good long-jump or by convenient stepping-stones. It is time well spent to look closely at these large and small drainageways, for they demonstrate the most significant geological process presently at work on the Iowa landscape the action of water. Rivers construct distinctive, flat-floored corridors known as alluvial plains which are underlain by water-transported deposits. These topographic corridors weave throughout the state’s other landform regions, but together they constitute the last of Iowa’s seven physiographic regions, the Alluvial Plains.

During the tens to hundreds of thousands of years since the various Pleistocene glaciers melted from Iowa, rivers have carved the state’s valleys and partially filled them with layered deposits of gravel, sand, silt, and clay. The streams draining Iowa’s land surface today range in size from small rills on upland slopes to the broad Missouri and Mississippi lowlands along the state’s western and eastern borders. Only these largest segments of the Alluvial Plains region stand out at the scale of the map. These drainage networks transfer water and sediment from the highest portions of the watershed downslope through increasingly larger streams and rivers and eventually to the Mississippi delta in the Gulf of Mexico.

For more information on the Alluvial Plains: Click Here!

 

 

Author: Jean C. Prior

Edited by: Drew Hutchinson

 

 

Tags: , , , , , , , ,
Last modified on July 11th, 2017
Posted on June 15th, 2017