Underwater forest remains in peril
By Gary Wisby
Chicago Sun Times
A cluster of about 50 stumps, rooted on the bottom of
Lake Michigan, is all that's left of a grove of trees
that was swamped by the rising lake 8,300 years ago.
Now the prehistoric stumps themselves are threatened--by
zebra mussels, the pesky little shellfish best known for
clogging water intakes.
The striped mollusks attach to the soft wood and have
formed a growing colony.
"Eventually the weight is going to potentially break
off pieces of the wood," said Michael Chrzastowski,
a coastal geologist for the Illinois State Geological
The stump grove is the only one discovered so far, but
many others doubtless lie on the lake bottom along the
banks of ancient rivers. Carbon dating of the wood would
tell researchers when water levels rose, killing the trees.
"Different elevations and different times the trees
died would give us more data points on the history of
lake-level change," Chrzastowski said.
The grove is about 15 miles east-southeast of Navy Pier,
in 80 feet of water.
Salvage divers using sonar accidentally found the underwater
woodland in 1989. They were looking for planes that crashed
and sank while being flown by pilots learning how to land
on aircraft carriers during World War II.
Trees on the Olson Site, named after lead diver Alan
Olson, are oak and ash. Carbon dating showed their age
at 8,300 years.
That told researchers when water covered the area again
after an absence of some 1,700 years. In the meantime,
one could walk the land--and trees could grow--between
what is now Chicago and the state of Michigan.
Protecting lake-bottom forest remains from zebra mussels'
depredations won't be easy.
First order of business would be to find the stumps before
the mussels whittle them down to nothing.
"The problem with that is, this is a needle-in-a-haystack-type
thing," Chrzastowski said. "We would need to
map all of southern Lake Michigan, and that would be time-