The Phenomenon of the Seiche

Great Lakes Seiche High tide

Great Lakes low tide due to seiche

By Rebecca Ruger-Wightman

Extreme low tide can be a beachcomber’s friend, but this great beachcombing windfall usually comes at a price to those on the opposite side of it, if it’s caused by a seiche. Picture a child playing in a bathtub, or many children frolicking in a swimming pool. The swaying back and forth of the water is essentially a seiche, which occurs with some frequency on lakes and bays in a much larger scale.

A seiche (pronounced "saysh") is a long wave that can be caused by any weather pattern pushing on water and stacking it on one end, like that water in the bathtub. Once the storm has moved on, the piled-up water surges back. This hundreds of miles of sloshing, from one end of the lake to the other, can go on for hours, or days. The wind set-up that pushes the water level up at one end of the lake will make the level drop by a corresponding amount at the opposite end. It can be compared to the storm surge caused by hurricanes along ocean coasts, but the difference is that the contained body of water will send the surge oscillating back and forth, and storm surges don’t see a reduction of water at some opposite end.

In some of the Great Lakes and other large bodies of water, the time period between the "high" and "low" of a seiche can be as much as four to seven hours. Because it is very similar to the time period between a high and low tide in the oceans, these are often mistaken as a tide.

seiche diagram NOAA Great Lakes tides

Graph courtesy of NOAA Great Lakes Environmental Research Laboratory

Lake Erie, because of its shallowness and position (the wind often blows exactly along the length of the lake from the southeast to the northeast) is known for seiches. If ice is not a constraining factor, wind or air pressure changes can cause the entire surface of a lake to rhythmically rock back and forth for a period of time. Eventually, gravity and the passing of the wind or storm will settle the lake back to horizontal.

Lake Superior sees sometimes continuous seiches, but they are small enough to go largely unnoticed. Larger seiches can bang boats together in harbors and send waves crashing over sea walls. Seiches have been recorded on each of the five Great Lakes, and occasionally they are deadly.

An October 1844 seiche from a few days of rough winds brought a wall of water in the city of Buffalo NY from Lake Erie, flooding parts of the city and killing 78 people. The passenger ship, Julia Palmer, carrying 300 people, had left Buffalo the previous night but was driven back toward the city. The anchor eventually caught and had her rolling and tumbling before the ship might have been pushed actually into the city with the high waters as some other boats were. At one point, a horse was sent from the steamer and swam ashore bearing a message attached to its mane that said the passengers and crew had burned all the wood and were now burning the furniture. The Julia Palmer was eventually pulled into port a day or so after the great flood.

Because the surge of a seiche may come without warning, the 45,000 people assembled in Grand Haven State Park, Michigan to celebrate the Fourth of July in 1929, had no idea that an early morning storm would wreak so much havoc later in the day. The storm produced a seiche that generated 20-foot waves. The pier was completely overrun by the waves, and several people were carried away either by the wave or the strong accompanying rip current at the park’s beach. Ten lives were lost to Lake Michigan that day.

A decade later and 20 miles south, a huge amount of water that two days before had plied the Wisconsin shore, now returned to Holland State Park, Michigan in the form of 10-foot waves that stole people from the beach, piers, and boats. Five lives were lost to the seiche of July,1938.

Seiches are by no means exclusive to the Great Lakes. They have swamped Venice and St. Petersburg, from the Adriatic and Baltic Seas, respectively. Nagasaki Bay in Japan sees seiches regularly—in 1979 three people were killed by the incoming seiche waves.

Seismic seiches are similar to wind/weather driven seiches but caused by earthquakes, and those earthquakes don’t need to be very close. Different from ocean tsunamis where giant sea waves are created by a sudden shift in the ocean floor, ‘seismic seiche’ was first used in 1955 to define the fluctuation of lake levels in Norway and England after the Assam, India earthquake of 1950. Earthquakes can generate seiches thousands of miles away, as evidenced by the numerous and far reaching seiches following the powerful 9.2 earthquake that struck Alaska in 1964. Swimming pools sloshed as far away as Puerto Rico, and seiches with waves as high as 6 feet were recorded on the Gulf Coast.

The high-water end of the seiche is called wind set-up and at the opposite end of this is the wind set-down, the low water level, which is relative to the height and rise of the seiche. This can result in extreme low levels with water disappearing from beaches and harbors, boats essentially dry docked, and large swaths of the lake floors available for beachcombing, if only for a short period of time.

lake erie water displacement

Graph courtesy of NOAA Great Lakes Environmental Research Laboratory

An October 2011 non-fatal seiche on Lake Erie showed parts of the lake bed that hadn’t seen the light of day in decades. One woman who lived on the lake south of Buffalo, and who normally would have 20-25 feet of beachfront, claimed on that day she could walk ‘hundreds of feet’ out before she saw water, though it did get muckier the further she went. She beachcombed for several hours, searching lake bed areas she’d never seen exposed, before the water began to roll in again, back to normal level only 8 hours later.

Fatal seiches are far less common as more municipalities have erected greater sea walls, or break walls out in the water that act as buffers. Dams, reservoirs, and harbours are sometimes designed by engineers who’ve studied the seiche phenomena as necessitated by location and occurrence. But just imagine the treasures to be found at the beach, if only the water would get out of the way, even for a little while.

This article appeared in the Glassing Magazine November 2017 issue.

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