A decade of warm winters with sporadic snowfall has failed to refill the snow-dependent Great Lakes, with falling water levels bringing the top ever closer to the bottom in Lakes Michigan and Huron.
The ebb has raised cries to dredge harbors, cost lake freighters small fortunes and meant trouble for breakwaters, which can survive the fiercest storms but won't suffer exposure to the air.
As the lake floor unexpectedly peers up through shallow spots, experts and observers say the situation has offered a dramatic lesson in the ancient machinery that empties and refills the Great Lakes.
It is gravity, and in the lakes, it is working on a massive scale.
A billion years ago, North America tried to tear itself apart, and the leftover rift became the Great Lakes. Dying mountains and sprawling mud flats filled it with sand and shale.
A continentwide glacier tamped it down next, then filled what remained as it melted 10,000 years ago. That water has been replaced 100 times over, continuously shoved out by more recently melted snows.
The system is time-tested and works well, provided it's fueled properly.
When snows are small and sporadic, problems arise, said Scott Thieme, chief of Great Lakes hydraulics and hydrology for the Army Corps of Engineers in Detroit. Last winter's spotty snowfalls are a good example.
"It [was] just melting in pieces instead of one big slug in the spring," Thieme said. "We just didn't get a huge spring ride--it wasn't doing bad in the April-May time period, but it did suffer in the summer time period."
Not too long ago, the lakes were brimming with water. Levels sloshed far above average in 1986 and 1997 in Lakes Michigan and Huron--technically considered the same lake because they rise and fall together.
The snow that supplies them blankets forests in central Ontario and Interstate Highway 70 in western Ohio. From Minnesota nearly to Montreal, the land works to feed the lakes. Yet because the area is so big, the lower lakes sometimes live separately from the lakes upstream.
Lakes Ontario and Erie are flourishing at average levels this year, after a series of dying tropical storms dumped what was left of their water on them in 2005. Lake Superior, on the other hand, is in drought, as is northern Lake Michigan, and the upper lakes are suffering accordingly.
Posted by Dave at September 3, 2006 10:38 AM