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Geology of the Indiana Dunes

Located in northwestern Indiana along the southern shore of Lake Michigan, the Indiana Dunes are a fantastic display of aeolian (wind) processes at work.

Incredibly tall sand dunes line the shores, and dune fields from former lake highstands extend even further back away.

These impressive ‘beach mountains’ originated from glacially transported sediment post-last glacial maximum [Pleistocene, ~18-14,000 yrs ago]. Glacial deposits are typically very poorly sorted but can become sorted by water (outwash), wave action, and wind action.

The dunes are primarily medium-grained quartz with finer-grained magnetite, so they are rather well sorted by specific weight. It would require wind ~15 mph to move this sized-sediment. 

Dunes typically have gentle upwind faces and steeper downwind faces [which is what generates the classic look of cross-bedding].
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However, some dunes may become ‘blowouts,’ which is when a pristine dune has been modified, potentially by human activity/movement. Instead of having a linear or slightly concave down front face, the dune can become concave up in the direction of the wind and have a much steeper front slope.

However, the Indiana Dunes are being starved at sediment and now are at risk. As is evidenced by the large number of blowouts, the dunes are not healing themselves too well. Due to longshore drift,
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he source of the sand for the dunes comes from the NE. As there is a large nuclear power plant along the shore toward the NE, the plant is likely blocking and prohibiting sand from traveling past it. Combined with this fact, negative feedbacks, human use, and other factors may be causing the starvation of these dunes.

All photos by author; graphics are linked to original sources

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