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Tag: seiche

  • Searching for the Seiche

    Searching for the Seiche

    A rock and ice face in Dickson Fjord after its collapse.

    On 16 September 2023, seismometers around the world began ringing, registering a signal that — for 9 days — wobbled back and forth every 92 seconds. A second, similar signal appeared a month later, lasting about a week. Researchers tracked the signal’s origin to a remote fjord in East Greenland, where it appeared a glacier front had collapsed. The falling rocks and ice triggered a long-lasting wave — a seiche — that rang back and forth through the fjord for days.

    Simulations showed that a seiche was plausible from a rockfall like the two that caused the seismic signal, but, without first-hand observations, no one could be certain. Now a new study has looked at satellite data to confirm the seiche. Researchers found that the then-new Surface Water and Ocean Topography (SWOT) satellite and its high-resolution altimeters had passed over the fjord multiple during the two landslide events. And, sure enough, the satellite captured data showing the water surface in the fjord rising and falling as the seiche ricocheted back and forth.

    It’s a great reminder that having multiple instrument types monitoring the Earth gives us far better data than any singular one. Without both seismometers and the satellite, it’s unlikely that scientists could have truly confirmed a seiche that no one saw firsthand. (Image credit: S. Rysgaard; research credit: T. Monahan et al.; via Eos)

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  • Suspended Sediments in Lake Erie

    Suspended Sediments in Lake Erie

    Lake Erie’s Long Point is outlined in turquoise in this natural-color satellite image. The pale color is likely due to limestone sediments in the shallow waters getting resuspended by a seiche or other disturbance. A seiche is a standing wave that forms in a partially- or fully-bounded body of water; in Lake Erie they are typically wind- and weather-driven. (Image credit: J. Stevens/USGS; via NASA Earth Observatory)

  • Prehistoric Seiche

    Prehistoric Seiche

    Sixty-six million years ago, a meteorite impact in modern-day Mexico wiped out the dinosaurs and most other living species of the time. To call the event catastrophic feels like an understatement. At the site of impact, rocks and animals were vaporized. Further away, molten rock condensed into glass beads that form a geological layer found around the world.

    Still further away, in what is now North Dakota and was then the bank of a freshwater river, scientists have discovered a deposit full of saltwater fish, sharks, and rays that would have lived in the vast inland sea (A) that stretched northward from Texas. The meteorite’s impact pushed these creatures kilometers upstream against the river’s natural flow.

    One possible explanation for the inundation is a tsunami. But geological evidence indicates the deposit took place within 15 minutes to two hours of the impact, when glass beads were still raining down. To travel the 3,000 km from the point of impact would take a tsunami on the order of 18 hours – far too long.

    Instead, the deposit is likely the result of a seiche (pronounced “saysh”) – a type of standing wave that occurs in an enclosed or partially enclosed body of water. If you imagine water sloshing in a cup or a tub, that’s essentially what a seiche is, but this was on a much larger scale. (For an example, check out this insane footage of an earthquake-induced seiche in a swimming pool.)

    What set the seiche to sloshing are the seismic waves triggered by the meteorite impact. They would have reached this site 6-13 minutes after the impact and triggered waves on the order of 10m. As the waves drove up the riverways, they carried dead and dying sea creatures with them, leaving them stranded on the riverbank until scientists uncovered them tens of millions of years later. (Image and research credit: R. DePalma et al.; via The Conversation; submitted by Kam-Yung Soh)

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    Making Waves

    A standing wave is created in a wave tank by fixing a wall at one end and moving the other wall–the wave generator–at a frequency such that the outgoing waves are superposed on those reflecting back from the wall. This doubles the amplitude of the wave. In the standing wave (also called clapotis), the surface rises and falls in a mirrored pattern: troughs become crests become troughs and so on. When the wave generator is turned off, the standing wave’s energy dissipates and eventually the tank stills. The sloshing motion that persists in the meantime is known as a seiche, which commonly occurs in nature in lakes, seas, bays, and any partially enclosed body of water. Some definitions include tides as a form of seiche due to the periodic nature of the moon’s force on Earth’s waters. See this animation of a seiche for more. (submitted by Daniel)