BY ANNE STANTON
TRAVERSE CITY — If Lake Michigan seems low now, try 8,000 years ago.
That's when an ancient river connected Grand Traverse Bay to Lake Michigan, shouldered by a land bridge that stretched from the end of Leelanau Peninsula to Norwood in Charlevoix County, said Hans Van Sumeren, director of the Great Lakes Water Studies Institute.
At that time, Lake Michigan was 175 feet shallower than it is today, he said.
Northwestern Michigan College students discovered the ancient river after they mapped the bottom of West Grand Traverse Bay using an echo-sounding system with millimeter precision, he said.
The ancient river connection to Lake Michigan already was known; nautical charts showed the river as a straight line.
"In fact, it looked like the Boardman River, a meandering river; it was just underwater," Van Sumeren said. "That was a piece of fascination, it was so well preserved."
The river ran as wide as 200 feet and as deep as 80 feet, he said.
Students who mapped the river in the summer of 2011 saw the enormity and complexity of glacial history and the dynamics of Lake Michigan, dynamics still at work today, with Lake Michigan dipping nearly six feet since 1964, he said.
The students' earlier work on mapping the Sleeping Bear Dunes Lakeshore shoreline and islands earned them an appearance on a National Geographic documentary, Drain the Great Lakes. The work was to help park officials understand the dilemma of avian botulism, Van Sumeren said.