Geologic Processes

There are essentially two types of landscape present in Indiana. In the southern portion of the state, a hilly landscape dominates. In contrast,the central and northern parts of the state are mostly characterized by flat glacial till. In this section of the page, we will examine both geologies and their respective features. In addition to this, we will examine a few other landscapes and features found in Indiana. See the relief map and satellite photo below in relation to the text.

A note to the viewer on interpretation of the false color satellite image: the color red is representative of vegetation (vegetation appears bright and water appears dark), the color green represents sediments in water, and the color blue is emitted Infrared Radiation (heat).

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Relief Map & Satellite Map courtesy Johns Hopkins Applied Physics Laboratory.

Central and Northern Indiana

In the Northern parts of the state, the casual observer might come to the conclusion that there is no geology of note, barring the occasional stream valley. While this is certainly a logical conclusion given the circumstances, upon closer examination we can discern many geologic features, and from these, determine what the history of the region is. During the last ice age which started between 3 and 2.5 Ma and extended to 11,000 years ago, glacial ice extented and retreated from the midwest several times. In all these instances, the ice reached its equilibrium point (the point at which the ice melts as fast as it advances) at or before present-day central Indiana. This means that all the particles (glacial "till") carried in these "dirt machines" was dumped where it stood over Northern Indiana when the ice melted. Before the most recent ice ages, there were others that had carved hills and valleys into the bedrock in addition to normal water and wind erosion during non-glacial periods. The bedrock of Indiana is limestone, dolostone, sandstone, and shale bedrock that was deposited primarily during the Paleozoic and Mesozoic eras (see accompanying map #1 and geologic timescale below);* of note: at some point, even the igneous basement rocks of the midwest were eroded. As the glaciers advanced, stalled and eventually melted, they compacted sediments into the valleys, deposited sediments at the foot of the advancing glacier, and left huge amounts of glacial till and "outwash" (glacial till picked up, sorted, and redeposited by meltwater streams). Once the glaciers had retreated for their final time, a plain of till now known as the Tipton Till Plain was left covering the bedrock of the entire central third of the state with a thick layer of sediment. An interesting fact concerning the flat-land stereotype: even the early 20th-century geographer C.R. Dryer referred to the terrain of central Indiana as so flat one "may ride upon the railroad train for hours without seeing a greater elevation than a haystack or a pile of sawdust." A moraine/kettle lake landscape was left by the rapidly retreating glaciers in the Northern Portions of the state along with (see maps #2 & #3 below).

 

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Maps #1 and #2: © 1966, Rho Chapter, Sigma Gamma Epsilon.

Map #3: © 2004, Nathan Scott; Map #4: © Indiana Geologic Survey.

Geologic Time Scale © 1966, Rho Chapter, Sigma Gamma Epsilon.

 

Southern Indiana

As previously mentioned, the southern portion of the state is a certain contrast to the rest. While up to 80 percent of present day Indiana was covered by ice during the most recent (Wisconsinan ice sheet) advance, the rest was open to the blue sky, or muddy water, as it turned out. With behemoth glaciers melting mere miles North, the southern regions of the state were cut into ribbons by meltwater floods and/or built up by depositional sediments. These erosional/depositional processes produced both the uplands such as the Mitchell plain, and the Wabash lowland and simlilar areas. As shown by the maps above, the area that falls between the Southern-most limits of each successive glaciation is covered with a relatively thin layer of glacial sediment, as it was only covered by the Illinoian. The area south of the limit of the Illinoian ice sheet is not covered with glacial sediment at all, excepting outwash.

In addition to the glacially influenced features of Southern Indiana is te karst landscape. A karst landscape is one in which the bedrock (limestone) is being, or has been, dissolved by acidic groundwater. This causes the development of caves, and the dissolution of joints in the rock. Within the caves, the dissolved ions in the water form spectacular formations over time such as the delicate soda straw or the massive Stalagtites shown below. On the surface, a karst landscape is very distinct (see maps below). It is often rough due to dissolution of joints in the bedrock, it may have streams that seem to "disappear" into holes between joints (see below), and is almost always speckled with sinkholes from collapsed caves. Partial collapse of caves can also form natural arches of rock that was not as completely dissolved as that that collapsed around it.

 

 

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Above Left: 1999 Aerial Orthophoto of Karst Area 4km West of Oolitic, Indiana © 2004, Microsoft Corporation.

Above Right: 1978 Topographical Map of the same area. © 2004, Microsoft Corporation.

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Above Left: Soda Straw in Scott Hollow Cave, West Virginia ©Ed McCarthy & Carl Samples

Above Right: Large stalactite in Scott Hollow Cave, West Virginia © Ed McCarthy & Carl Samples

Middle Earth Cave, West Virginia © Ed McCarthy & Carl Samples

 

This website was prepared as an assignment for Geosciences 211 (Physical Geology) taught in the spring of 2004 at Earlham College, Richmond, Indiana.

Copyright 2004 Earlham College. Revised May 4, 2007 . Send corrections or comments to scottna@earlham.edu