Said Eliza Reid, the first lady of Iceland, quoted in "Iceland Is a Magnet for Tourists. Its First Lady Has Some Advice for Them. Eliza Reid, a former U.N. tourism ambassador and the wife of President Gudni Johannesson, welcomes her country’s many visitors, and has a few suggestions on safety, respect and how to meet locals" (NYT).
The waves here are so sneaky, they come creeping up on you and suck you in if you are standing too close - nothing can be done to save people if this happens - so please be extremely careful if you visit these beaches, and never turn your back to the sea and the waves....
The staff at Svarta fjaran - the Black Beach restaurant by Reynisfjara, say that they often go down to the beach to warn people against playing in the waves, only to be sneered at and scolded for trying to ruin the holiday of these people!
One American oceanographer distinguishes "rogue waves" as occurring on the ocean and "sneaker waves" as occurring at the shore, while the National Oceanic and Atmospheric Administration loosely defines rogue waves as offshore waves that are at least twice the height of surrounding waves and sneaker waves as waves near shore that are unexpectedly and significantly larger than other waves reaching shore at the time. Scientists do not yet understand what causes sneaker waves, and their relationship to rogue waves, if any, has not been established.