environmental history
introduction geography geology cultures ecosystem conservation

Project goal:  Help sustain the natural resources and protect cultural resources of the Driftless Area.

geology and biology
Driftless Area

The flowing water of streams especially during periods for melting of the continental ice sheets during the various advances of the Pleistocene epoch help cut deep valleys into the bedrock of the Driftless Area. Limestone escarpments and sandstone bluffs rise above the otherwise flat landscape of the Midwest. The groundwater dissolves and erodes the limestone to create solutional cavern and cave systems below the surface. Further dissolution and erosion opens up sinkholes on the surface at the tops of bluffs. The faces of stream valley limestone bluffs break away and the pieces of limestone bedrock roll down the hillside breaking into smaller pieces and accumulating near the base of the slope. These pieces of rock are known as talus. The crevices at the top of the bluff and the accumulation of talus at the bottom of the slope make up a mechanical karst system.  The interconnected voids under the mechanical karst store air that is colder than the outside air during the summer and warmer than the outside air during the winter. Ice can also accumulate in the talus voids during the winter.  The unique karst topography with the deep air and ice spaces allows the warm air to be drawn in at the top of the bluff where it is cooled, sinks, and flows out through vents on the lower slope.  This process is reversed during the winter with warming and rising of air through the maze of talus spaces. The cold air producing talus slopes are known as algific talus slopes.  The coldest of these slopes are those with a north and northwest facing aspect where the ice is insulated from the sun.  See the photograph below of an algific talus slope and the cut away illustration to the right showing how the air is cooled in the karst topography.  It may not be necessary for the mechanical karst system in the valley to be connected to the upland solutional karst system.  The ice blocks may persist all year on north facing slopes.  Sinkhole plains with solutional caves and algific talus slopes from by mechanical karst are common in the Driftless Area. The springs from groundwater discharges at the base of the slopes help maintain a cold water fishery in the streams. These valley streams support trout, sculpin, suckers, and other cold water aquatic life unique to the Region.

This geologic resource also provides mining opportunities for early Native Americans and European settlers.  The limestone bedrock of the Driftless Area contains layers of lead and zinc ores. Changes in water drainage in the limestone bluffs over geologic time created deposits of lead and zinc minerals in between the limestone layers and in the caverns. The ore and metal deposits attracted Native people and pioneers miners to help settle in this region. There are many examples of historic mine shafts and mine openings around the Driftless Area.


The photograph above is of an algific slope in northeastern Iowa.  There are a couple of people on the slope to give you a sense of scale.  Pieces of the rocky limestone bluff have broken free and accumulate on the slope.  These pieces of rock or talus fit loosely together allowing for the circulation of the cold air.  A thin layer of soil forms on the loose rock which is covered mostly with lichens, mosses, liverworts, and ferns shaded by the trees and cooled by the moist air.  These slopes are sensitive to disturbance because it takes long periods of time to form the soil or thin organic substrate for colonization by shade tolerant plant species.  The photograph below shows the vent openings amongst the talus on the lower slope.  Larger openings formed by the karst topography were used as openings into the bedrock during the historic mining period.        The photograph above is of a maderate cliff.  Maderate cliffs are   steep because they do not have a large accumulation of talus at the bottom of the slope.  Maderate cliffs can have cool moist surfaces too especially for north facing cliffs.  Cold water springs commonly occur at the bases of algific talus slopes and maderate cliffs.  The photograph below shows a spring at the base of the maderate cliff pictured above.  Nutrient recycling is critical in these rocky habitats for plant development so outside sources from industrial air emissions wtih excess nitrogen may create an imbalance.  Land snails play an important role in nutrient recycling by breaking down coarse organic matter such as leaves.  The algific talus slopes are a great example of a geologic resource regulating the biological diversity in an ecosystem.    



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