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Landscape Features of Iowa

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Landscape Features of Iowa he topographic features seen in this brochure illustrate the range of pictur- Tesque 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. Under- Gary Hightshoe, Iowa State University standing the geologic setting of various Landscape types of terrain is essential for citizens concerned with farming, urban expansion, This island-braided channel of the Mississippi River occupies a recreation, excavation of mineral resources, gorge eroded through steep rock-lined bluffs in Clayton County. pumping of groundwater supplies, The deeply entrenched river valley was shaped by glacial Features landfilling of waste materials, and other meltwater floods between 18,000 and 9,500 years ago. environmental and natural resource issues. Also, it is useful to think about these land- scapes in terms of their influence on the Continuous rock bluffs distribution of native plant and animal called palisades line the Upper Iowa River. These habitats, on various soil types, on the cliffs result from the river potential for archaeological remains, and on eroding against dolomite, a patterns of historic settlement. Learning resistant rock unit formed 450 million years ago. more about the features of Iowa’s landscape Such scenic landscapes in increases our understanding and apprecia- northeastern Iowa reflect sedimentary bedrock close FRONT COVER tion of the views around us and the earth to the land surface. Turkey River Mounds State Preserve beneath our feet. Clayton County Gary Hightshoe, Iowa State University Photo by Gary Hightshoe, Iowa State University Jean Prior Shifting sand dunes occupy part of an abandoned channel of the Upper Iowa River in Allamakee County. The sand accumulated when water flowed here earlier in the valley’s history. Wind also deposited sand during later dry periods. Pat McAdams The oldest bedrock formation visible in Iowa outcrops at Gitchie Manitou State Preserve in Iowa Department of Natural Resources Lyon County. The distinctive reddish Geological Survey Bureau Sioux Quartzite is 109 Trowbridge Hall seen here at “Jasper Iowa City, Iowa 52242-1319 Pool,” an 1800’s- www.igsb.uiowa.edu of Iowa Gary Hightshoe, Iowa State University era quarry on the preserve. These Educational Materials: EM-28 (2001) The Iowa River forms sweeping meander loops as it flows durable, quartz- across its floodplain in Iowa County. Earlier migration rich rocks are 2.6 channels are visible in the fields and woodlands. Flood- billion years old. plains are underlain by porous alluvial deposits that yield Glacial erratics of this formation are easily recognizable valuable groundwater supplies. These shallow resources are and may be found many miles to the southeast. vulnerable to contamination from the land surface. Some of Iowa’s most fascinat- ing scenery is found in the Loess Hills. Alternating Ocheyedan Mound is an peaks and saddles diverge This inside view of isolated conical hill composed along ridge crests sculpted a cave entrance at of sand and gravel. It is an from thick deposits of loess Maquoketa Caves excellent example of a glacial carried by wind from the State Park illustrates Greg Ludvigson kame, formed as meltwater broad Missouri River valley. an example of carried sediments off the gla- The loess originated as silt, karst topography. cier surface and into a cavity left in the valley following Such features also in the slowly melting ice. glacial meltwater floods include springs and between 12,000 and sinkholes, Doug Harr 50,000 years ago. landforms that result from groundwater movement slowly dissolving Don Poggensee shallow limestone or dolomite bedrock. Jean Prior Gary Hightshoe, Iowa State University Crooked ridges with steep sideslopes characterize the An outcrop of Loess Hills of western Iowa. Circular depressions, some filled with water or clumps of trees, sedimentary They are composed of thick mark the location of sinkholes in this Clayton County aerial view. rock displays deposits of silt carried by wind Sinkholes form by collapse of thin soil and unstable rock into horizontal from the adjoining Missouri underground crevice or cave openings. Shallow aquifers are layering, River valley during seasons vulnerable to which reflects when glacial meltwater flood contamination in the rock’s sediments were exposed. A this geologic setting. origins in a sharp contrast exists between Though most marine prairie and encroaching common in environment. Vertical fractures, caused by later earth stresses on the woodlands in this topo- northeastern Iowa, brittle dolomite, contribute a blocky appearance to the outcrop. These graphic setting. sinkholes also are various planes of weakness are flowpaths for ground-water seen in Floyd and movement. Mitchell counties and in the Burling- ton area of south- eastern Iowa. Tim Kemmis Hump-backed ridges Gary Hightshoe, Iowa State University These wetlands are a series of rise from the land- glacial kettles at Doolittle scape in southeastern Linn County. These Prairie State Preserve in Story Gary Hightshoe, Iowa State University County. A subtle drainage ridges, known as system connects them, as noted by paha, are always the soil moisture and darker oriented NW to SE. vegetation patterns. The linked They are all that remain of a once “prairie potholes” trace a route Pat Lohmann taken by glacial melt-water Dendritic drainage patterns crease these cropped fields higher glacial plain through disintegrating glacial with branching routes along which precipitation runoff and are often capped ice 13,000 years ago. is channeled into rills, creeks, and rivers. This effective with wind-blown loess drainage network has reshaped the glacial plains left and sand. after southern Iowa’s last contact with glaciers, over 500,000 years ago. Gullies are deep, narrow erosional cuts through the landscape. Their Stan Mitchem development and Pat Lohmann growth is an active geologic Glacial erratics are boulders of igneous A glacial moraine process within the and metamorphic rock, native to regions in Dickinson County silt-dominated north of Iowa. The erratics in this Black appears as a series of Loess Hills Hawk County pasture were carried into irregular broken topography of Iowa by glaciers over 500,000 years ago. ridges crossing the western Iowa. Gullies widen and lengthen They were concentrated at the land landscape. These are headward (upslope), eroding quickly, especially surface by later erosion, which removed Gary Hightshoe, Iowa State University hummocky accu- after heavy rains. the fine-grained deposits once sur- mulations of pebbly debris that settled out of stagnant, rounding them. slowly melting glacial ice about 13,000 years ago..
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