Great Lakes Fluctuations Sometimes Extreme Forecasters warned this week about the possibility of seiches on Lake Michigan. Seiches — oscillations that shift the water level, usually minutely — are common occurrences on the Great Lakes. But in extreme cases, they can cause a huge water level drop-off.
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Great Lakes Fluctuations Sometimes Extreme

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Great Lakes Fluctuations Sometimes Extreme

Great Lakes Fluctuations Sometimes Extreme

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ROBERT SIEGEL, host:

You're listening to ALL THINGS CONSIDERED from NPR News.

We noticed in a recent Chicago weather report, in addition to thunderstorms and some dazzling cloud-to-ground lightning, a series of minor seiches in Lake Michigan. Seiches, spelled S-E-I-C-H-E-S, are evidently common fair in the Great Lakes and in other, lowercased G, great lakes. But for those of us who live far from a great inland body of water, the seiche is an exotic word and an exotic phenomenon.

And joining us to explain what it means is Dr. Stephen Bortone who directs Minnesota Sea Grant, which is part of the University of Minnesota. He's in Duluth. Welcome to the program, Dr. Bortone.

Dr. STEPHEN BORTONE (Director, Minnesota Sea Grant, University of Minnesota): Oh, thank you.

SIEGEL: And first of all this word, S-E-I-C-H-E, seiche, I've read that it comes from some Swiss-French dialect.

Dr. BORTONE: Yes. It seems to be the - somewhere around the 1890s that was coined. The word slosh might be better for an American to say. But, you know, that seems to be the word we have adopted.

SIEGLE: When there is a seiche or a slosh in Lake Michigan, what is it? What does it look like?

Dr. BORTONE: Well, it's really a standing wave. There's two kinds of waves. One that you're all familiar with or everybody's familiar with, called the progressive wave. And that's the one you typically see on the shoreline, where a wave comes along, breaks and splashes. Then there's a standing wave in which there's no net movement of water in a large body. But basically, it's - water moving back and forth. The best analogy is water sloshing around in your bathtub.

SIEGLE: Or having a basin of water and tipping it back and forth.

Dr. BORTONE: Exactly.

SIEGLE: Well, I know why it happens in the basin or in the bathtub. Why does it happen in Lake Michigan?

Dr. BORTONE: Well, there's a lot of causes, anything that would set up water motion. An earthquake could do it. Some very large meteor hitting the water body could do it. But most of the time, it's due to things like storm fronts moving through and then quickly subsiding, or sometimes, heavy rains could cause it, or even winds that blow very strongly and then quickly stop. And that's probably what's been happening recently in the Lake Michigan situation.

SIEGLE: You mean, so the weather is so remarkable at one end of the lake - the very large bathtub - that it affects the level of the water at the other end of the lake or the bathtub.

Dr. BORTONE: Correct. And what would, I guess the visual image would be you push water up against one side and then quickly release that. Push from the wind, and then it sloshes back to the other side. Takes quite a while for it to happen, maybe a few hours in some cases for it to slosh back.

SIEGLE: Are we talking about standing waves, which are at their highest are inches or feet or many feet? How big can a seiche be?

Dr. BORTONE: Well, they happen all the time. And in they're in the matter of inches. And you don't notice them and no one cares. But when they get to be a few feet or more, then we start noticing their impacts along the shorelines.

SIEGLE: We did see an account of one seiche in Lake Superior, where the level -the water level went down by three feet over the course of a quarter of an hour. And lots of boats were...

Dr. BORTONE: Right.

SIEGLE ...stranded as a result.

Dr. BORTONE: Yeah, it can do that. It can even pick boats up and put them on top of docks. And it causes other boats to smash into each other as they move from side to side. So there's a fair amount of destruction that can take place.

SIEGLE: And I gather, folks who watch weather reports in and around the Great Lakes, for them this word is not strange.

Dr. BORTONE: No. It's fairly common. In fact, Minnesota Sea Grant's newsletter is called The Seiche. We have adopted that as sort of our way of communicating with the public. But it's a fairly common word. A lot of people know it. I'm not sure they always understand what the causes of them and that sort of thing. And the fact that they are out there all the time, they're not just such of a magnification. We can actually see them.

SIEGLE: Well, Dr. Bortone, thank you very much for talking with us about it.

Dr. BORTONE: You're welcome.

SIEGLE: It's Dr. Stephen Bortone in Duluth, who is director of Minnesota Sea Grant, part of the University of Minnesota, explaining seiches to us.

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