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Shorelines! Shorelines! Everywhere! – Pt. 3

Submitted by Patty Kostro


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At one time, if you were standing in Gary on our present shoreline and looking north, you would not see the shoreline of Lake Michigan. You would not see the lake because, the shoreline was much further north. It was about five miles further north. And, if you were standing in the same spot about 12,000 years ago, you would be submerged in water! This is because the ancient shoreline was approximately eight miles south of the present shoreline.

Northwest Indiana has three different distinct shorelines that were created as the glacial lobe retreated and advanced allowing lake levels to dramatically change over a period of 10,000 years.  

The first major shoreline was created approximately 14,000 years ago from the waves on the southern shore of Lake Michigan eroding the moraines. A moraine is a mass of rocks and sediment carried down and deposited by a glacier, typically as a ridge. Remember, glaciers act like bulldozers. They scrape and pluck at the bedrock as it moves forward, but once it retreats, it leaves all rock and sediment behind. These “piles” of rock are the moraines. Due to the moraines on the southern shore of Lake Michigan, the first shoreline was created. It is called Glenwood Beach and in some areas it is nearly 8 miles south of our current shoreline! 

The second major shoreline called Calumet Beach was created due to changing lake levels. The lake levels dramatically dropped. This occurred because “outlets” opened up many miles north in Canada due to the ice retreating. Outlets are best described as drains. These drains had been blocked or plugged by ice, but when the ice begins to melt, the drains open up and allow the water to flow into other areas like streams, rivers or other lakes. Hence, as the outlets opened up in the northern part of the lake, Lake Michigan began to “drain out”. This phase allowed the bedrock along the sides of the lake to be exposed. But, only after a few hundred years, the ice advanced again, blocking the outlets. This caused the lake level to rise again. As the lake levels began to rise, the waves eroded at the exposed bedrock creating sand and sediment. The currents along Lake Michigan are called longshore currents. Longshore currents bring sand and sediment down the western and eastern coastlines of Lake Michigan to northwest Indiana. All of the sand and sediment that was eroded from the exposed rock was carried down to our shores and deposited in the southern part of Lake Michigan. All of these factors, along with waves and wind allowed our earliest dunes to be built and our second major shoreline, Calumet Beach, was created. This shoreline can be followed along Highway 12 from Michigan City to Dune Acres and can be observed along Ridge Road (hence, the name) from Glen Park through Highland and Munster.

Around 10,000 years ago the lake levels dramatically dropped again. At one point the lake was approximately 100 feet less in elevation. The lake would not be seen from our vantage point! This phase lasted for about 4,000 years. However, the lake would begin to rise again. It reached over 23 feet higher in elevation than it stands today. If the beach communities (Beverly Shores, Dune Acres, Ogden Dunes or Miller Beach) existed at the time, you would be under water! It was at this time period around 6,500 years ago that the beginning of the third major shoreline, which is our current shoreline, Toleston Beach started its formation. This shoreline incorporates dunes, marshes, and beach ridges and will be the topic of next month’s blog.

Did you know that ancestral Lake Michigan was called Lake Chicago?


Glacial Retreat

The Great Lakes as they appeared from 14,000 years ago until 7,000 years ago. Image modified from the US Army Corps of Engineers and Great Lakes Commission.


Shorelines

The three major shorelines (Glenwood Beach, Calumet Beach and Toleston Beach) along the southern shores of Lake Michigan in northwest Indiana. Image courtesy of www.igs.indiana.edu.

You can read about more “Geology of the Dunes” right here!


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#geology #glaciers #moraines #shorelines

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