Our Ancient (?) Shoreline

By: Sandra A. Remis

Special thanks to guest speaker Frank Pranschke, who presented a VERY informative talk and slide show. “Lake Chicago, Lake Michigan, Our Ancient Shoreline,” at the EHS Annual General Meeting on March 25, 1995, at the Edgewater Branch Library.

Mr. Pranschke has a M.S. in Limnology, the scientific study of the life and phenomena of lakes, ponds and streams. He has received grants from the U.S. government, the National Geographic Society and a Fellowship at Northeastern University. He is a member of the Chicago Rocks and Minerals Society. His talk covered the discovery of an early submerged forest in southern Lake Michigan, alias Lake Chicago, and the lake in general.

Pranschke related that, in June of 1989, three Chicago-area salvage operators, using sidescan sonar in search of shipwrecks, located a cluster of unusual bottom features in Lake Michigan.

They were at a depth of 80-85 feet, about 15 miles S-SE of Chicago Harbor. Divers found the features to be a cluster of at least 50 tree stumps in growth position and limbs and trunks resting on the bottom. The stumps are generally cone-shaped, with a height of 1.6 to 4 feet and average diameter of 6 to 12 inches, the largest being 30 inches across. Exposed root masses were observed on two stumps in the 2.1 acre area. Additional stumps are likely buried in the locally numerous sand ridges.

Examination of sample stumps revealed the age of the trees by their rings, their type - ash and oak - and the fact they had, at one time, survived a fire. A core drill sample found clams 19 feet below the site surface, indicating that the forest had grown in a swampy area. The excellent preservation of the wood suggests that the site has been continually submerged since it was drowned.

Radiocarbon dating of one stump indicates drowning of the trees about 8,000 years ago, which is 1-2,000 years earlier than previously thought. This discovery provided significant new data on the history of the lake’s level between its extreme low phase, approximately 10,000 years ago, and the beginning of its last very high phase, approximately 5,500 years ago. The lake also could not have risen steadily, as once thought, because the forest took time to grow.

Mr. Pranschke then turned to a discussion of how the history of low and high lake levels affects Edgewater residents. It seems that once upon a time, 12-14,000 years ago, Clark and Ridge used to be Edgewater’s shoreline. Since then the lake level has fallen and risen, sometimes dramatically, in cycles, giving Edgewater more or less of a shoreline. The time in between lows and highs seem to be getting shorter.

Scientists studying Lake Michigan have developed disturbing theories about record high water levels swelling the Great Lakes. These researchers believe that lake levels were much higher before scientists started measuring them in the middle of the 19th century. They fear that the swollen lakes could rise more than five feet over the next 100 years.

Now five feet doesn’t sound like much, unless you realize that each one-foot rise in the lake can easily chew away 20 feet or more of beach, depending on the elevation of the land. The shoreline is not evenly elevated; it fluctuates with higher and lower areas. Granville Avenue at the lake, for instance, is a low spot.

Some of you will remember 1986, when the lake water rose two feet and was hitting the bulkheads of north Sheridan Road condos, sometimes flooding the lobbies. If you parked your car for any length of time on the lakefront that winter, your car was entombed in a block of ice that didn’t melt until spring. According to Mr. Pranschke, “Another two-foot rise in the lake and Sheridan Road would have been under water.”

Scientists believe that the entire century and a half period of record keeping - the period when most of the shoreline area was planned and intensively developed - could well represent a low cycle in the longer history of the Great Lakes. Geological evidence suggests that every 500 years over the last 2,000, Lake Michigan seems to have risen to about 585 feet above mean sea level, approximately 5.5 feet higher than its current levels, and stayed there for decades.

Although the theories are far from proven and further research is necessary, scientists predict that, if they are correct, beaches, homes, buildings and roads along the shorelines of eight states and Canada could be submerged. Vast stretches of the Chicago lakefront from Touhy south to Jackson Park - including Sheridan Road, Lake Shore Drive and much of the Chicago Loop - could be flooded. The Chicago River, artificially reversed in a landmark engineering feat in 1900, would disgorge massive torrents of lake water down through the Illinois River, causing floods along its length.

In a recent phone conversation, Mr. Pranschke noted: “From 1900 to the present, Lake Michigan has risen above the 580-foot mark three times - in the 1960s, 1970s and 1980s. The high in 1986 was 581.8 feet. As of June 1995 the mean lake Level was 579.5 feet. But those are calm water measurements. Sections of Lake Shore Drive had to be temporarily closed several times in the last year when storms caused six-foot waves to crash over the roadway.”

Somehow the prospect of Edgewater’s shoreline receding halfway back to where it was over 12,000 years ago, at Clark and Ridge, doesn’t appeal to me. As a Sheridan Road condo owner, I’ve taken pride over the last decade in telling people that I live on the Lake. I do hope that my statement needn’t be taken literally any time soon.