Wait for it - this one is The Biggie. It will be hugely enormously colossal. It will happen - sooner or later, so pray it will be after your lifetime. There is a massive chunk of an island in the Canaries, called La Palma, which is unstable. It WILL ( not might) drop off its base, and a trillion tonnes of rock will smash into the sea in a few minutes. This is calculated ( in an article in the New Scientist) to result in ten tsunami waves, one after the other, each at least 50 metres high when they reach the coast of the USA (and probably the Caribbean and possibly the northern coasts of South America. ) That's about 160 feet high or more hitting the USA. . Total devastation will result for at least a hundred kilometres inland. This unbelievable water-power will sweep round the Atlantic coasts until it reaches all other coasts, including Greenland, Iceland, Western Europe and Western Africa. The power of the water hitting Britain will probably not be even one-tenth of what hits the USA, but it will still be terrifying.
Thank goodness I live on a ridge, well inland !
There may be devastating surges into the Mediterranean.