Heading north from Kansas City, I-29 rolls across the Glaciated Plain, dropping frequently to cross the many streams that flow westward into the Missouri River. On that warm, sunny morning of April 2, a purple haze of henbit shimmered over the barren fields and small flocks of wild turkey fed among the corn stuble. At one stream crossing, a red-shouldered hawk rose from the valley floor, a four-foot black snake in his talons.
Just south of Mound City, the highway drops onto the Missouri River floodplain, winding northward at the base of the Loess Hills. These heavily dissected bluffs, formed by an accumulation of glacial dust, line the east side of the floodplain from northern Missouri to Sioux City, Iowa; they also rise along the west edge, from Omaha northward. Crossing into Iowa, the interstate leaves the hills and drifts into the middle of the floodplain which has grown to a width of 6 miles at that latitude. Once covered by extensive wetlands, river meanders and oxbow lakes, the rich floodplain is now a mosaic of cropfields; vital wetland habitat, so important to migrant waterfowl and shorebirds, is now restricted to a chain of refuges along the River's valley. One of these, the DeSoto National Wildlife Refuge, straddles the Nebraska-Iowa border, about 20 miles north of Omaha. Centered on an oxbow lake, this refuge teems with migrant geese and ducks in the fall; my visit in early April turned up only a smattering of waterfowl and a small flock of American white pelicans.
Further north, the Missouri River floodplain balloons to a width of more than twenty miles. There are three reasons for this dramatic increase in dimension: glacial ice, flooding and soft sediments. Lobes of ice from the early Pleistocene Glaciers entered this area, creating a wide valley that was later used by the Missouri. Entrenched there later in the Epoch, the Missouri was fed by enormous quantities of meltwater as the Illinoian and Wisconsin Glaciers retreated; the river was much larger during that period and underwent frequent floods. In the course of flooding, rivers often produce new channels, change course and widen their banks. If the surface rock and sediments are soft, as they were in this region (i.e. glacial till, loess and Tertiary sediments) the river can produce a wide floodplain; should the river become entrenched in more resistent bedrock (e.g. the limestone of Central Missouri), the river cuts more deeply and less broadly (the Missouri River Floodplain is less than 2 miles wide near Columbia).
