IOWA - Portrait of the Land - Land: A Geologic Inheritance

If you had been looking for a very long, geologic time,
you could have seen the continents themselves in motion,
drifting apart on their crustal plates, held afloat by the fire beneath.

The land is our foundation. And that foundation sits on a deep geological inheritance that has been unfolding for eons. One individual usually can observe only small natural changes to the landscape in his or her lifetime. We may see a brief moment, a scratch on the surface, of that dynamic earth history. But if enough small events, and occasional larger ones, continue for a very long time, they can combine to literally transform the face of a continent.

Iowa's landscape, both visible and underground, still bears the signatures that tell the story of the geologic forces that shaped our state. We can study their bold, unmistakable inscriptions on the surface where we live. But if we read between the lines and interpret the footnotes, we also can understand the deeper, hidden layers of older, buried landscapes and seascapes. The ancient sea floors, coral reefs, shore lines, coastal swamps, tropical river systems, melting ice sheets, and wind-blown dust produced the earth materials that form the backbone of Iowa's land.

Today we work this land, or perhaps we should say the land works for us. It grows our food, supports our buildings, provides raw materials for our industries, absorbs our wastes, and stores our water supplies. Therefore, we need to understand what this ground beneath us is like - what holds it up, what gives it shape and texture, what finite resources lie within its depths, how vulnerable it is to contamination sources, and whether it can heal itself if we damage it. Armed with this basic geological information, we can begin to comprehend how much the land and its characteristics affect our daily lives. And we can let the land itself guide our sensible use of its many resources and our quest for solutions to environmental problems.

Iowa's landscape itself attests to the underlying geology. A change in terrain usually indicates a geologic change beneath the ground. Most of what Iowans see - elevation, drainage, and soil composition - are the products of glacial activity. For example, in the southern half of the state, rolling hills stereotype Iowa to many cross-state travelers. These are the familiar scenes from Grant Wood paintings, with cropfields and pastures, farms and towns. How many people realize that glaciers set this pastoral scene more than 500,000 years ago? Erosion later carved deep valleys through the layers of pebbly clay, and wind-blown silt mantled the terrain. Sometimes, the valleys cut deep enough to reach bedrock, exposing coal seams and tropical plant fossils formed 400 million years ago, when the land was a maze of coastal swamps.

Prehistoric people lived and farmed along the streams and on the hilltops. Newly arrived settlers and their descendants tucked cities beside the rivers and built farmsteads on the uplands. Farm ponds and reservoirs, like Red Rock and Rathbun, now supplement the region's scarce groundwater supplies. Despite the rolling terrain, careful farmers learned to protect the land. They trim their cropfields with terraces and waterways, grow hay on the steeper slopes, raise cattle on the grasslands, and protect the oak-hickory forests. Without such vigilance, landowners might lose their topsoil to erosion and their woodlands to trampling by livestock.

Along the state's borders, two great rivers - the Missouri on the west and the Mississippi on the east - dominate the land and its geologic history.

The broad floodplain of the Missouri speaks of torrents of glacial meltwater. During summer months, from about 31,000 to 12,500 years ago, the floods spread for miles across the valley. In winters, the melting slowed and the waters receded to expose dried silt and mud. Fierce west winds whipped the fine deposits into the air, then piled the loess in thick blankets along the eastern side of the valley, eventually forming the Loess Hills. The windblown dust also spread eastward, falling in thinner layers across much of the rest of what now is Iowa. The process was copied, on a smaller scale, along many of the state's other rivers.

Muskrats are at home in the glacial wetlands that dot north-central Iowa (Bjorkboda Marsh, Hamilton County). Photo by Roger Hill.

Habitats of Iowa's plant and animal communities are a result of differences in earth materials and geologic history.

The ridged hills of deep loess in western Iowa contain some of the state's best remaining tracts of native prairie. Photo by Don Poggensee.

The passage of cool, moist air through
creviced dolomite bedrock in northeast Iowa
forms rare habitats (algific slopes) for plants
that normally grow much farther north
(Dubuque County). Photo by Bob Howe.

The Loess Hills sheltered Native Americans, who lived in the protected valleys, hunted on the open prairies, and fished in the rivers and oxbow lakes. Lewis and Clark marveled at the abundant wildlife of these hills two centuries ago. Pioneers brought cattle to graze on the native grasses and worked tirelessly to drain and plow the river bottoms. Later, in an effort to tame the floods along the Missouri and its tributaries, engineers straightened some streams and built levees to confine their flows.

As human tampering sped the water along, the riverbeds cut deeper and banks eroded. Nearby wetlands dried up as their water seeped away through the sandy underground connections between the river and surrounding land. Still, the aquifers hold ample water to supply wells both for irrigation and for drinking water.

Despite changes in the Missouri River, the mystique of the Loess Hills endures. Unique in the western hemisphere, the Loess Hills lure a host of visitors: scientists studying unusual plant and animal life; families seeking home sites; developers marketing the scenery; contractors in search of fill dirt; and recreationists who want to hike or bike or camp or hunt along prairie ridges or secluded woody slopes. The unusual terrain and biological features of the region have prompted talk of national protection and further recognition.

An equally dramatic river valley rules our eastern border. But bedrock, rather than loose silt, dominates the Mississippi Valley. Outcrops of rock that formed on tropical seabeds 300 to 550 million years ago now define the Mississippi Valley and dictate the sharp bends and narrow canyons of its tributaries. Some streams have cut deep channels into the rock during the 500,000 years since the region's last glacial encounter. Spectacular blufftop overlooks, hidden caves, springs, white-water creeks, and colorful fall leaves attract tourists. Numerous quarries tap the readily accessible limestone. One prominent rock outcrop, the Silurian Escarpment, winds from Iowa all the way to the east end of Lake Erie, where it cradles Niagara Falls.

But the same rock formations that shape the scenic topography of Iowa's "Little Switzerland" also mandate caution in use of the land. Fractures, fissures, and sinkholes in the rock can channel surface water directly into valuable underground aquifers. A manure or chemical spill could pollute a trout stream, upset the delicate balance of the area's unique biological habitats, or permanently taint the drinking water of thousands of people.

In north-central Iowa, the terrain offers a whole new set of challenges and opportunities. Here, farmers praise the flat, black, productive soils, while naturalists tout the pothole marshes and glacial lakes. We see a young landscape with dry, knobby mounds and shallow, wet bowls - the "tracks" of glaciers that melted just 13,000 to 12,000 years ago. Valuable deposits of gravel and sand lie where they were strewn by the glaciers or meltwater streams. Those pulses of water from the decaying ice also formed wide valleys that now carry much smaller rivers.

But the glaciers left much of north-central Iowa's land tabletop flat, without a distinct natural drainage pattern. To make the fields dry enough for farming, people stepped in to help hurry the water away through drainage ditches and through clay and plastic tile. Indeed, for more than a century, landowners have tiled, ditched, and drained the region to convert its marshes to some of the world's premier farmland. Water now runs off the land through these drainage ways instead of soaking into the sponge-like wetlands.

Alongside, and beneath this northern Iowa pothole country lie landscapes once locked in permafrost. To the east, in a fifteen-county region centered on Waterloo, weathered boulders still work their way to the surface. These stones, carried from the north during an earlier glaciation more than 500,000 years ago, lie scattered in pastures or piled by farmers in fencerows. Abundant groundwater reaches the surface in springs and rivers and in peaty wetlands, called fens, which also support rare plant and animal communities.

In the northwest portions of Iowa, most evidence of the tundra and glaciers has been covered by layers of windblown loess and modified by erosion from a network of streams. Broad valleys and open uplands roll to the horizon, reminiscent of the ranch country of the Dakotas. But time and weather have exposed tips of the state's oldest bedrock, the Sioux Quartzite, which pokes to the surface in northwest Lyon County. The ancient reddish rock formed from sediments in coastal waters more than 1.6 billion years ago. The famous Pipestone quarries in southwestern Minnesota are in this same distinct red rock formation, which is regarded as sacred ground by Native American tribes. Ironically, the state's youngest bedrock - sandstone, shale, chalk, and limestone less than 100 million years old - lies directly against the oldest. These "newer" sediments formed in shallow seas confined by cliffs of the old Sioux Quartzite.

While it may challenge our senses to imagine such geologic forces at work over eons, Iowans can watch some landscape changes happening every day. For example, up to 10 percent of the state's surface is in floodplains, where flowing water carves valleys and deposits sediment along ever-changing river corridors. The Flood of 1993 dramatically showed many Iowans the geologic power of moving water.

We also can try to visualize past events that have shaped Iowa streams. The relatively wide valleys of the Des Moines, Skunk, and other rivers suggest the huge volumes of water that scoured their channels as the ice sheets melted. Some people have witnessed the formation of oxbows and backwaters following floods. The wind still sculpts active sand dunes in a few places along the Mississippi, Upper Iowa, Des Moines, and Cedar rivers.

People tend to think of the landscape as permanent and stable. But Iowa's floodplains, hillsides, gullies, and even fractured bedrock are dynamic and changing. Sometimes people have become a major force in those changes. We now have the technology, the equipment, and the power to shape our environment - sometimes subtly, sometimes dramatically, sometimes purposefully, sometimes unintentionally. We have become geologic forces, as anyone knows who has watched a dam being built or seen a road construction crew at work.

Just look around Iowa. It is one of the most intensively used and frequently disturbed landscapes in the country. Even farmers, who turn over only the upper few inches of most of our landscape every year, have assumed earth-moving powers. Thus, while we live on an earth fashioned by nature and time, we've often used our machines, and our whims, to alter the environment around us.

The landscape is where all human activity takes place, and learning to live with it is essential. If we understand its building blocks, however - the bedrock, the soil, the water, the air, and their inherent relationships - then we can protect the land and its heritage, our heritage.

RHYTHMS OF LIFE

Essay and photo by Lowell Washburn

At first glance, the winter marsh appears as void and uninhabited as the dark side of the moon. The temperature hovers near zero, and at this season there is no din of bird song to greet the rising sun. As you stroll across the silent expanse of this frozen world, you suddenly get the feeling that this particular piece of real estate is no less remote than a Canadian wilderness.

But first impressions can be deceiving. A closer inspection reveals that the marsh is criss-crossed by a myriad of bird and mammal tracks. These tracks are the winter chronicles of the furred and feathered denizens that call this place home. It is here, in the stark freshness of last night's snowfall, that a human explorer can find nature's version of the daily newspaper. Like most good papers, the snow features information on social gatherings, social strife, and tragedy. It tells where the pheasants are roosting, which weed seed buffets are currently most popular with local rodent populations, and where a resident weasel has set up headquarters beneath a forgotten rock pile.

But for those who desire to go beyond the light reading, animal tracks can also provide a glimpse into a world that urbanized humans have largely forgotten. It is the harsh reality of predator and prey, a realm where the world is neatly divided into two categories. One is the hunter, the other the hunted. In this high-stakes game of survival there are no politics, no trade-offs, no compromise. There is simply a winner and a loser.

The tense balance between predator and prey is amazingly delicate. And in spite of intense human pressures on the environment, the fragile rhythm somehow endures. The basic premise is simple. Prey species, such as mice and rabbits, have a stunning capacity for reproduction. Predators, like the fox or hawk, do not.

Follow the tracks and you'll see how the system works. Here, in the fresh snow, are the briefly recorded episodes of close encounters, hard chases, and near misses. Sometimes there is a widening pink spot in the snow where one life has ended so that another might continue. This uneasy relationship - this struggle for survival - becomes the very essence of the rhythm of life.

The latest set of tracks offers a good example of the rhythm in action. Near the edge of the cattails, a hungry rabbit has ventured into the open to girdle bark from a clump of sumacs. This obviously foolish move does not go unnoticed by the adult redtail perched in a nearby oak. The hawk, also hungry, bobs its head and launches the attack. Sensing its mistake, the winter-lean rabbit flees for cover. Although the escaping animal is soon covering ground with impressive two-foot leaps, the hawk is already halfway across the marsh. As the redtail closes, the cottontail begins a series of evasive maneuvers that buy a few more seconds of life. The raptor mimics the moves and at last the forms converge.

A rabbit dies. A hawk feeds. The natural rhythm continues.

		An Amish farmer and his draft horses work the land together near Sharon Center in southern Johnson County. Photo by John M. Zielinski.
Ancient Iowans were drawn to places where the land speaks in scenic eloquence (Turkey River Mounds State Preserve, Clayton County). Photo by Gary Hightshoe, Iowa State University.

Iowa's land is a rich mosaic of cropland, pasture, timber, and a long rural heritage (Saints Peter and Paul Church in northeast Johnson County). Photo by Drake Hokanson.		Gentle slopes, extraordinarily productive soils, and timely rains enable a bountiful soybean harvest. Photo by Photographic Services, University of Iowa.

	The abundance of grain and pasture also favors livestock production, such as this inquisitive herd of sheep. Photo by Photographic Services, University of Iowa.