Geology of the Dunes Uncategorized

Why did the area look like a washboard? Beach ridges and Swales! – Pt. 5

April 4, 2016

Submitted by: Patty Kostro

In the January blog we discussed some of the geologic landforms that helped shape the eastern part of our shoreline from Ogden Dunes to Michigan City, primarily the Great Marsh. This month we will look at what was forming along the shoreline from Ogden Dunes into Illinois.

In the area west of Ogden Dunes, our shoreline (in some areas) was approximately 8 miles further inland from where it stands now. The same types of coastal processes occurred along this part of the beach which included a barrier beach and a lagoon. However, there was a dramatic change to this part of the shoreline due to the addition of beach ridges and swales.

What are beach ridges and swales?

Beach ridges are linear sand ridges that run parallel with the shore. They are formed by the deposition of sand and sediment due to wave action and lake levels. There are three different types of lake level cycles that Lake Michigan endures: a 30-year cycle, a 150-year cycle and a 600-year cycle. Each individual beach ridge formed during a 30-year lake level cycle. They are a geologic indicator of time and serve as “markers” of when the shoreline was added as the lake levels were falling overall. However, during this 30-year cycle, the lake level would fluctuate and it was during this time period that a beach ridge would form.

We have over 100 beach ridges that are west of Ogden Dunes. If you were looking from the sky before our area was developed, it would have looked like a washboard. This “washboard” appearance is due to a succession of parallel beach ridges. A series of ridges forms a strand plain. And, within the strand plains, there are not only the beach ridges, but there are swales too. You can think of swales as troughs. They are the depression that is between the beach ridges. These areas would have been considered wetlands or marsh. However, due to industry and the development of northwest Indiana, almost all of these were filled in as our area was being urbanized.


Ridge and Swale


There are many organizations that have committed to restoring some of the remaining “dune and swale complexes” to their natural habitat along with removing invasive species. One of these organizations is Shirley Heinze Land Trust which has nature preserves in Lake, Porter and LaPorte Counties. One of these preserves is called the Seidner Dune and Swale and is located in Hammond, Indiana. This area is filled with a very diverse ecosystem and will give you a clearer picture of actual beach ridges and swales as they would have looked prior to industrialization.

Other Dune and Swale Complexes to visit: Ivanhoe Ridge and Swale in Gary

Also, if you are interested in celebrating the completion of the Oak Savanna Restoration Project, a hike is being led by Save the Dunes along the Miller Woods trail in the Indiana Dunes National Lakeshore on May 26th. Healthy oak savanna habitats allow ecologically significant species to thrive. Click here for more information about the hike and to learn about black oak savanna habitats.

You can read Patty’s previous posts right here!




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