Shorelines want to be straight.
Or at least that is what our lead coastal geologist at the Illinois State Geological Survey will tell you. What he means by that is the many points and peninsulas that crop out of a shoreline are usually the first things to be eroded, while sediment tends to accumulate on the up-current side, both of which create a straight(-er) shoreline. The sand that makes it around these obstructions continues slowly south down the Illinois shore until it hits a really big obstruction: the south end of the lake. There, the sand has been accumulating for thousands of years where the Indiana and Michigan Dunes currently are located.
This is a simple explanation of a complex process, but it does a pretty good job of explaining the large-scale phenomena of sediment movement on the great lakes over a long period of time.
Speaking of large-scale phenomena that happen over long periods of time…Google Earth has a sweet time lapse thing that stitches together images from 30 years of satellite photography. It shows stuff like…sand moving down Lake Michigan’s coastline!
But how exactly does that sand move? Is it linear? How long does it take the average sand particle to make it down? Where does sand get held up? Where does it flow freely? Does it cycle?
These and other questions are what we are currently studying in a large coastal project primarily being executed by the ISGS, but which involves several other agencies. We are gathering several types of data over the entire Illinois Coast to try to gauge how that sand is moving, who is going to be affected by it, and what can be reasonably done to control that movement. We are just beginning, but we have learned a lot so far.
But if you want a very grainy (pun!) picture of how it works, check out this time lapse from Google Earth’s Earth Engine here. (Make sure you press the “Play” button!). This link shows sand moving southward along Illinois’ Lake Michigan Coast after the construction of a marina and a beach north of Illinois Beach State Park. Pumped down the coast by the rhythm of wind and waves, this time-lapse shows the Lake’s heartbeat–a cardiogram of the coast. The wrinkles of the coastline are being smoothed out over time.
I am a bit partial to the Illinois Coast, having worked here for the past year. I have been learning how beautiful it really is. But, as Google Earth shows, there are a lot of beautiful places on God’s Green Earth.
Check out these cool and interesting (and sometimes depressing) time-lapses before you go!
- Tangier Island in Virginia, slowly being lost to erosion, quickened by sea level rise
- The demise of Earth’s (former) 4th largest lake/sea
- Rondonia, Brazil, expanding into the forest
- Coastal Expansion in Dubai
- Shrinking of Arctic Ice Sheets
- Rapid urbanization in China
- A Meandering River in the Amazon (shown in GIF above)
- Or check out the Case Studies page for global-level changes