06/11/2026
STILL SHIFTING…
Isostatic rebound has already transformed the Great Lakes before, and it is not close to done.
The Great Lakes basin is still tilting toward the southwest.
GPS measurements show that the northeastern side of the basin continues to rise relative to the southwest as the landscape adjusts to the weight of the Laurentide Ice Sheet.
Ten thousand years ago, the upper Great Lakes drained differently than they do today. Water flowed northeast through outlets that are now stranded hundreds of feet above modern lake levels. As the basin tilted, those outlets were abandoned. Ancient shorelines were lifted. Rivers changed direction. Some lowlands were flooded while others emerged from the water.
Eventually, the modern drainage system developed through the St. Marys River, St. Clair River, Detroit River, Lake Erie, Niagara River, and St. Lawrence River.
And the tilting continues.
In broad terms, the continuing tilt favors the modern drainage route through the St. Marys, St. Clair, and Detroit rivers.
At the same time, the basin is gradually tilting away from the Niagara and St. Lawrence rivers.
But isostatic rebound is only one force at work. Niagara Falls continues to carve its gorge upstream, while erosion, climate, and future glaciations will also help shape the Great Lakes of the future.
The past reminds us that change is inevitable.
Lake levels have shifted by hundreds of feet. Ancient outlets have closed. New ones have opened. Rivers have reversed direction. Entire drainage networks have been reorganized.
Could Niagara someday carry less water than it does today? Could water eventually find a different route toward the Mississippi basin?
No one knows for sure.
The Great Lakes were made by the Ice Age, but they are still very much a work in progress.
Image: Created by Dr. Michael Craymer (Natural Resources Canada) and Chris Wisotzkey (NOAA National Geodetic Survey) to illustrate how the Great Lakes basin is tilting due to Glacial Isostatic Adjustment.
