How Lake Erie got its groove
2/8/2006Maybe there was a creaking noise first, some sign of the extreme pressure bubbling under the mountain of ice.
Or, given the millions of gallons of water surging forward under the glacier's crushing weight, perhaps it was more of a scream.
A new theory contends that around 19,600 years ago, probably somewhere near Cincinnati, the edges of the last ice sheet to cover Ohio gave way.
The moment was explosive.
According to the theory, millions of gallons of trapped water gushed forward from as far away as Lake Ontario. Propelled by the weight of the glacier itself, the torrent broke through the wall of ice in jets like giant rooster tails before shattering the glacier's southern edge. Ice chunks the size of apartment buildings cracked loose and swirled madly in the sudden flood surging into the Ohio River Valley, cascading into the Mississippi, and finally dumping into the Gulf of Mexico.
Just before the flood, in the flatlands of northwest Ohio, pressures built. The shallow basin of Western Lake Erie acted as a bottleneck of sorts to some 300 miles of water buiding up to the northeast beneath the glacier.
When a flood some 18 miles across finally broke through, the glacier heaved, briefly becoming the world's biggest iceberg before smashing down again. A torrent squeezed over Kelleys Island and around it, carving grooves in the island's bedrock and the surrounding lake bed.
In fact, the grooves at Kelleys Island are the linchpin of a theory formulated by a group of researchers from the University of Toledo and Kent State University.
"This teeny-tiny site [of Kelleys Island] tells you about the whole area behind it," said Mandy Munro-Stasiuk. The KSU professor is the lead author of a paper in the recent issue of the journal Quaternary Science Review.
"The Kelleys Island grooves are absolutely without a doubt one of the most spectacular features [of this type] I've ever seen," Ms. Munro-Stasiuk said. "When I first saw these, I drooled."
By looking at the grooves, the researchers theorized the presence of a giant flood. Such a flood not only shaped the Kelleys Island grooves and similar marks on the lake bottom, but molded the jutting arm of the Marblehead Peninsula and other shoreline features at the same time, they say.
The theory discards earlier notions - such as the one you may have seen in your elementary school science textbook - that the glacier slowly carved the 360-foot-long scar in the rock of Kelleys Island.
According to this older theory, ice studded with boulders and gravel acted as a router and sander, shaping the smooth furrows.
But when Ms. Munro-Stasiuk of KSU and Timothy Fisher of UT looked at the 33-foot-wide, 10-foot-deep trough on the Lake Erie Island, noting its curving edges and sinuous walls, they saw water, not ice, as the sculptor.
"This jumps right out at you," Ms. Munro-Stasiuk said. "It's exactly like the kinds of things I see in riverbeds ... it's pretty obvious." The Ph.D. geologist has studied the work of ancient water and glaciers fro more than 15 years.
The idea that glacial meltwater played at least some role in the carving has been gaining currency in publications as early as 1979. But the ideas of Mr. Fisher and Ms. Munro-Stasiuk are far more dramatic. Previous theories focus not on a Genesis-class flood, but on brief but sudden surges of debris-laden meltwater.
That's just not enough water, Ms. Munro-Stasiuk says.
"You can't just have that little rinky-dinky melting of the ice sheet."
And thuse another chapter in a family feud of glacial geology is born, pitting the floodites and the gradualists. It's a classic battle, actually, with threads that reach far back into the 19th century, and basic notions of how the Earth was formed. The question: are the Earth's features molded more often by gradual processes that worked over long time frames, or by sudden, catastrophic events?
Ms. Munro-Stasiuk knows gradual processes are important, but she sees a larger role for catastrophe than her gradualist brethren do. The flood she theorizes is one such catastrophe.
Carrie Jennings, on the other hand, is a gradualist. Sweeping explanations rouse her suspicions. Let's not oversimplify, she says. It's always more complicated than that. And that's how she sees this new theory of a giant food. "They're making a leap," Ms. Jennings said. She has a Ph.D. in glacial geology and is a senior scientist for the Minnesota Geological Surveys.
You don't need to involve Lake Ontario, or even all of Lake Erie, to create the grooves, she said.
"You can have one of these releases of subglacial flood water from a region of the bed, not the whole Lake Erie."
But you may need both Lake Erie and Lake Ontario in order to create grooves in both the island and lake bed, sculpt the Marblehead Peninsula, and shape the surrounding lakeshore. All of those features bear the mark of a single event, the UT-KSU team contends, because each bears the same east-west orientation.
"The orientation of the Marblehead Peninsula is identical to the Lake Erie grooves. These features are all oriented in exactly the same direction. They are all formed by processes that moved almost exactly east-west," Ms. Munro-Stasiuk said.
But Ms. Jennings counters that the orientation may reveal no more than the orientation of the bedrock into which the grooves were carved.
"Whey can't that be controlling the orientation of these furrows? I don't buy into [the notion that] the consistency of the orientation justifies" theorizing that a big flood caused the grooves. "That's a bedrock issue. All the bedrock is oriented in that direction."
But Ms. Munro-Stasiuk objects that the bedrock in this region is oriented north-south, not in the east-west direction of the grooves. Fracture lines in the rock are similarly north-south.
Ms. Jennings says the new theory also suggests an unstable situation, with the glacier floating atop a surging flood. Under those conditions, the glacier should have floated away.
"That's where they get into the realm of the physically impossible. When you have that much flow, what's holding the ice sheet back? It would just totally decouple from the bed. Why is it not floating away like an iceberg? I can't even wrap my head around that," Mr. Jennings said.
Rick Pavey, a geologist with the Ohio Geological Survey, is even more skeptical of the flood theory. In his view, glacier-carried boulders did the lion's share of the carving.
"I've worked in this area for quite a while, and all the evidence I've seen points to ice. Water can be involved - some of the sinuous forms [in the groove] are probably a result of water erosion."
But Mr. Pavey says at most, the impact of water is limited. Boulders remain the best argument, in his view.
Let me give you a little story. On Middle Bass Island (west and slightly north of Kelleys Island), tons of rock is exposed, he said. All of it is grooved, but the
grooves are a foot wide and a few inches deep. He followed one of the Middle Bass grooves as far as he could: Until I got to the rock that formed it. The rock was still
in place, a perfect fit.
In addition, the Kelleys Island site lacks what s known as lag deposit. Instead, glacial till - a mixture of clay, silt, sand, and boulders that glaciers leave behind
- shows up on the islands, he said, not a gravelly lag. If water had been responsible for the grooves, it would have carried away all the silt and sand, and left gravel deposits.
But Mr. Fisher and Ms. Munro-Stasiuk say sediment from the flood ended up in the Gulf of Mexico.
There are some huge fans [of sediment] in the Gulf and we don t know where they came from. There are some thick gravel deposits no one can explain. And right about this time frame, there is evidence for decreasing salinity in the oceans, Ms. Munro-Stasiuk said.
Mr. Fisher, a Ph.D. researcher who studies glaciers, looks to rocks where glacial carving is indisputable, such as in the Blue Creek Metropark near Whitehouse.
There, the bedrock is covered with innumerable parallel scratch marks, none deeper than a few millimeters. The glacier is planing the landscape, planing it flat, eroding it down, sheet by sheet, little bit by little bit. But on Kelleys Island, it s actually sculpting and building an intricate landscape, Mr. Fisher said. That s water. Ice doesn t do that.