Causes of Erosion

    For the past 12,500 years, the wave action taking place across Lake Michigan has caused the erosion of the shoreline between Racine and Chicago.  Sand, gravel, and sediment from the Pike River Delta of Kenosha has been moved farther south along the Zion and Waukegan coastline.  This movement and deposit of sediment, called littoral drift, is what eventually caused the beach ridge plain from Kenosha to Waukegan.  The cause of this erosion was a combination of three things;  waves, wind and lake level.

    Waves are the most important factor in the forming of the beach ridge plain.  First, the waves provide the energy to erode, move, and deposit the sediment.  Next, the waves shape the beach and the lake bottom near the shore.  Finally, they determine the shape of the shoreline. 

    Of course, the waves are dependent on the wind, which the majority of the time comes from the south.  However, because the northerly winds cause a higher wave height, they have the power to do more damage.  As the waves break along the beach, the sediment is moved across the beach in a zigzag pattern that pushes it towards the south.  We could see this pattern when we threw ping pong balls into the water. (see picture below)

    The third cause of the erosion we see here along the shore of Lake Michigan is the lake level.  The height varies about a foot from summer to winter.  When the water levels are high they cause severe erosion along the shoreline.  Lower levels cause erosion under the water near the shore.

    The working forces of wind, waves and water level over several years have caused movement of the sand and sediment which formed the beach ridge plain.  As you continue on your field trip, you will see the results of this erosion.