Question: What is a seiche?
This questions comes from the News Tribune newsroom. Before we answer it, though, let’s ask another question: How do you say “seiche”?
Because I didn’t know how to say it, and if you’re like me, it can be a frustrating reading experience if you don’t know how to pronounce the words.
It looks French, and I took a decade of French in school. I could guess at the French pronunciation — “sesh” — but I wanted to know how to say it in English.
This was the first question I put to Jay Austin, a professor of physics and astronomy at the University of Minnesota Duluth and a faculty member at UMD’s Large Lakes Observatory.
“I think most people say ‘saysh,’” Austin said.
It turns out that it’s probably Swiss French, according to several dictionaries, with possible connections to German. The word’s exact origins are obscure.
In any case, “saysh” it is. Let’s move on.
So, what exactly is a seiche?
“Seiches are caused when strong winds and rapid changes in atmospheric pressure push water from one end of a body of water to the other,” according to the National Ocean Service — though seiches typically appear on closed bodies of water rather than on the open ocean.
“When the wind stops, the water rebounds to the other side of the body of water. The water then continues to oscillate back and forth for hours or even days.”
Austin brought things down to scale for us.
“So, your cup of coffee on your desk — bump it really quickly, and you'll see the coffee in the cup slosh back and forth,” he said. “And it takes maybe a second for the coffee to go through one complete slosh back and forth in your in your cup.”
Simple enough. I do that every day, sir.
“If you have kids, or when you were a kid, you're playing in the bathtub, and you can move your hand back and forth in the tub and get the water sloshing back and forth, and that might take a few seconds for each full slosh to pass by.” Austin continued.
“The same exact thing happens in lakes, except that, of course, because of the scale that lakes are on compared to a coffee cup or your bathtub, it takes a lot longer. So, in Lake Superior, for instance, the wind can blow water toward one end of the lake or the other.”
In the fall or spring, Austin said, the typical weather systems often blow water toward Duluth, meaning lake levels are higher here, while somewhere like Sault Ste. Marie might see lower lake levels.
So, it’s seiche season on the Great Lakes.
“We're entering the season right now where we tend to have these big wind events to blow right down the axis of the lake and stack water up in Duluth,” Austin said.
The waves from a seiche on Lake Superior aren’t enough to cause flooding or damage, and that has to do with Lake Superior’s depth — though it’s more complicated than that, he said. On a shallower lake such as Lake Erie, though, seiches can cause damage to harbors, he said.
Seiches don’t really affect ships out on the lake, Austin said, because the changes in water levels are fairly small. But that doesn’t necessarily mean that the shipping industry doesn’t pay attention to them, he said.
Such as in 2007, for instance, when Lake Superior’s water level was near an all-time low.
“I'd be willing to bet that they paid an awful lot of attention back in 2007, because (seiches could) determine whether you can get boats in and out of the harbor.”
So, now we know! Next time you’re at your desk, do a little science and create a seiche or three. Just try and keep them in your coffee mug, OK?