Gazette Article by: Barbara Joyce
Appeared in the Gazette: Summer 1995
Local Expert Searches for Understanding
How many Winnetkans, walking along the shores of local beaches, know the following facts about Lake Michigan?
– There is an “underground forest” of oak, ash and hickory tree stumps submerged 15 miles off Chicago’s coast.
– The lake level is rising six one-hundredths of an inch each year due to glacial rebound.
– Homes with riparian rights have an erosional problem that requires expensive maintenance.
These and countless other lake shore issues are the work and study of Dr. Charles W. Shabica. A Winnetka resident, Dr. Shabica is a coastal geologist, coastal engineer, consultant, and professor in the Earth Science Department at Northeastern Illinois University.
He was contacted for his expertise in 1990, when divers found 50 tree stumps 85 feet below the surface of the lake. Three of the stumps were recovered for species identification and radio-carbon dating. They were found to be about 8,200 years old.
“My theory is that the stumps were probably buried under mud for most of their 8,000-year history,” said Shabica. “The preservation of them is so good. But exposure will wear them away in less than 1,000 years,” he said.
The trees grew during the early part of an extremely low, post-glacial lake phase known as the Chippewa low phase and then were submerged during the subsequent lake-level rise.
In 1993 Shabica received a grant from the National Geographic Society to map the forested area in detail. “What we have found out in that project is that the lake bottom is complicated. There’s an idea that it’s all the same. It just isn’t.”
On the site, Shabica’s team has found three bowl-shaped tree stumps. Two of them are filled with rocks; one actually resembles a perfect three-foot salad bowl. Shabica speculates that the bowls are either Native American artifacts or natural objects unusually abraded by water and sand.
The Illinois State Historic Preservation Agency (ISHPA) has given permission for Shabica’s team to go down to videotape the site and look for artifacts or bones, removing nothing. The divers are volunteers from the Underwater Archaeological Society.
“The discovery of the submerged tree stumps gives convincing evidence for low lake levels,” Shabica said. “We have lots of evidence for high lake levels. Now we see the bottoms of the curve.”
Shabica noted that the lake level is rising six inches a year. “At the present rate it will be five feet higher in 1,000 years. That’s not radically fast,” he said. “Hopefully coastal engineers will cope.” He added, “We won’t see a time when the lake level goes down five feet.”
“The public is still unaware that we have an erosional lake shore,” Shabica explained. “The big problem,” he said, “is that we don’t have enough sand…” “In fact,” Shabica continued, “very little historical information is transferred to property owners.”
“Shore protection must be maintained,” said Shabica. He refers to such protection as “armor,” which most people see as piles of rocks along a beach. The problem is the increasing cost. “If you have 100 feet of lake shore property, you’ll have to spend $100,000 every 20 years just to maintain the edge. It’s a maintenance problem that won’t go away.”