Geology of the Dunes

Shorelines! Shorelines! Everywhere! – Pt. 3

December 11, 2015

Submitted by Patty Kostro



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.


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

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



  1. Reply

    Tom Hjertquist

    December 11, 2015

    Great article, learning more all the time. I have to admit though she is my daughter; She love the dunes.

  2. Reply

    Kitty Bakken Johnson

    December 11, 2015

    I remember learning about the ancient shoreline along Ridge Road in northwest Indiana. I believe geography teacher Donald Ray (Griffith Junior H.S.) told us to look for the sand hills along Ridge Rd. that remained as an indicator of where the Lake Michigan shoreline was long ago. When I was young there were many places along Ridge Road where you could see these ancient sand dunes!

  3. Reply

    Mike Harding

    December 12, 2015

    Great blog yet again. I have learned things I never knew reading these blogs

  4. Reply

    Nancy Brown

    December 12, 2015

    Totally fascinating. I so appreciate this journey through time. The older I get the more I realize how little I know about our area. I remember as a kid riding down Ridge Road into Gary and admiring the beautiful homes that sat “way up there”. Thank you so much for the history lesson.

  5. Reply

    Gwen Ruge Lane

    December 12, 2015

    Hello Dig the Dunes,
    A friend of mine has been sending me your page and thought that we might have something in common in serving Northwest Indiana and Southwest Michigan.
    I am the owner of A Van-Go Chauffeur and Shuttle. I have a 15 passenger van I use now for wine and brewery tours and other events such as airports and weddings, etc.
    I’d love for you to contact me if you feel we might be able to get together and talk about the possibility of working together in some way.
    Sincerely, Gwen Ruge Lane

    PS. My cell is 219-921-3468

  6. Reply

    Jill Atkins

    December 12, 2015

    Thanks for the interesting article. My brothers and I inherited two lots near Porter Beach that are IN Lake Michigan! We still pay taxes on them too!! Not sure what we should fo with them.

  7. Reply

    Cathy Rough

    December 12, 2015

    Incredible article — fascinating, informative, and incredibly well-written. I look forward to more!

    • Reply

      Patty Kostro

      December 13, 2015

      Thank you Cathy!!


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