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Invisible but still cataclysmic internal tsunamis in the ocean or lakes have been shown to exist for the first time by researchers at Scripps Institution of Oceanography at UC San Diego and colleagues.

Graduate student Noel Brizuela led a group of oceanographers who examined the immediate and long-term effects of a landslide in 2006 at Lake Santa Maria Del Oro, a crater lake near Puerto Vallarta, Mexico. Using a 35-sensor array designed to measure the lake's wind-driven circulation, researchers demonstrated that highly energetic episodes in their data were in fact powered by landslides off the side of the lake.

Upon sliding down the lake bottom, underwater mounts were transformed into a dense fluid mixture of water and sediment and later transported by internal tsunami waves. Generated by landslide energy, these waves occur when deeper water has a higher density due to lower temperature or suspended sediment. Although they were as high as seven meters (23 feet) crest to trough, internal tsunamis were virtually imperceptible to observers at the surface.

The meaning of the data collected by the array had been unclear for more than a decade before Brizuela and colleagues reanalyzed it and discovered they were looking at the signature of a landslide.

"Underwater landslides are largely unpredictable and so had never been observed directly,” said Brizuela. “Our fortuitous measurements depict the subsurface effects of sediment mass failure with extraordinary detail and reveal fundamental processes that have yet to be represented in numerical models."

The study sheds light on elusive, subsurface phenomena that result from disruptive events such as submarine earthquakes or landslides. While surface tsunamis are notable for the devastating impacts they have on land, the energy of internal tsunami waves is confined to the ocean interior where it may have drastic consequences. Until they dissipate, internal tsunamis hold the potential to reshape vast swaths of the seafloor, alter large scale patterns in ocean circulation and threaten deep sea ecosystems, the researchers said.

Co-authors of the paper, published July 24, 2019 in the journal Scientific Reports, are Anatoliy Filonov of the University of Guadalajara in Mexico and Matthew H. Alford of Scripps Oceanography. 

– Robert Monroe