Submitted by Patty Kostro
Welcome to Geology of the Dunes! Each month, Patty Kostro will be teaching us something different about our lake, beaches and dunes. Feel free to interact on this blog, ask questions and make comments! This month she talks about Lake Michigan.
Winds across the lake can create majestic waves. A surfer’s delight!
The Great Lakes located in North America is the largest freshwater system on Earth. This massive body of freshwater includes Superior, Michigan, Huron, Erie and Ontario. These lakes have an economic impact and are used for industry, fishing, shipping, agriculture and recreation but, most importantly, our drinking water. The lakes compromise 84% of North America’s and 21% of the Earth’s surface freshwater.
Lake Michigan is the fifth largest lake in the world (by surface area). The shoreline covers roughly 1660 miles. Our “great lake” shares its shore with four states (Michigan, Indiana, Illinois and Wisconsin) and connects to Lake Huron through the Straits of Mackinac.
On clear days you can see the Chicago skyline across the lake.
The shoreline that surrounds the lake is made mostly of sand and pebbles due to erosion. And, how do we know that erosion occurred? Because, we can see evidence of the erosion all around the lake where tiny grains of quartz (sand) make up most of the sediment along the lake. Lake Michigan’s shorelines are filled with beaches and sand dunes. Most of the sand on our Indiana beaches is from erosion that occurred in Wisconsin and the U.P. of Michigan. The dunes around Lake Michigan are part of the largest freshwater dune system in the world.
Sand, pebbles and the occasional piece of beach glass can be found along our shores
It is the climate in our area that allows these dunes to be built. Sand dunes are formed from not only having a sediment supply, but wind and waves play an important role too. The northerly and easterly winds off of Lake Michigan can average 4 to 6 miles per hour, but during severe storms that occur from October to April, wind speeds can reach over 74 mph! Those winds have hurricane speeds and will do a lot of damage to our shoreline including wiping out entire dunes from all of the wave action.
The direction of the winds along with the type of current along Lake Michigan drastically changes the appearance of the shoreline. The northerly shores of Lake Michigan have high-perched dunes which sit on bluffs high above the lake in northwest Michigan, while the southeastern portion along Michigan and the southern shores of Indiana contain low-perched, parallel and parabolic dunes.
All of these types of dunes have a dune system. Our dune systems can be seen within the Indiana Dunes National Lakeshore where foredunes, wetlands and back dunes are all nestled away just past our beaches. However, at one time, the dune systems were much further inland. Some of the ancient dunes are up to 10 miles inland from our current shoreline.
So, how did all of this start? Glaciers. Our great lake was made due to the scouring and retreating and advancing of glaciers. This will be the topic of next month’s blog!
Places to see: • At one time Lake Michigan reached as far south as Ridge Road. As you head east from Broadway on Ridge Road and look to the south, you can see where houses are sitting on old dunes.
• Last October, Lake Michigan endured an extratropical storm that reached 74 miles per hour and thrashed against our shoreline. It carved away roughly 40 feet of a foredune between Ogden Dunes and Portage Beach! You can still see the detrimental destruction today.
The result of a fierce storm last October at Portage Lakefront.
Each month we will have a helpful hint. This month’s helpful hint is brought to you by the Tobacco Education & Prevention Coalition!
Did you know that it can take up 2-25 years for a cigarette butt to degrade? We need to protect the cleanliness of Lake Michigan and our beaches. Please contribute in cleaning up debris that is left on our shoreline.
Lake Michigan has many faces. Here it is calm and clear as glass.