They deposited huge piles of sand and rock debris when they melted, leaving behind the hilly terrain you see today. With the glacial landscape formed. Lake Michigan and many smaller lakes began taking shape. The level of water filling Lake Michigan's ice carved basin rose and fell many times before reaching its present level. Waves wore back the headlands.
Shoreline currents carrying sediments build sandbars and spits across bay mouths.
Sometimes sediments dammed bays, creating small inland lakes such as Glen Lake near the Lake Michigan shoreline. Prevailing westerly winds blowing across the lake build two kinds of sand dunes in Sleeping Bear Dunes. Beach dunes develop on low-lying shores of Lake Michigan. Their main ingredient is beach sand. The Aral Dunes, along Platte Bay's north shore, are good examples of beach dunes.