A Kelvin Wave Isn’t a Tsunami: It Lifts the Sea Along the Coast

Kelvin waves are not tsunamis. They don’t curl over and crash on the beach, which is the first thing the word “wave” gets wrong. A better image, as PBS NewsHour puts it, is water sloshing in a bathtub or a swimming pool during an earthquake. The point of that comparison is the motion rather than the cause: a broad displacement of water, not a breaking crest. In the ocean, Kelvin waves are bulges of water that lift the sea level as they move along the coast. The word doing the work there is “along.” The water is raised in a band beside the shore rather than arriving as a wall from open water, which is why the tsunami comparison is the one worth unlearning.