I know this sounds dumb ..6/7 ft high ? How could it do THAT much damage ?
6/7 ft high or 30 ft high, your typical wind generated wave has a fairly short length. These tsunami waves were more like the leading edge of a rise in the level of the water, like a storm surge in a hurricane. It just keeps coming and coming until it hits something taller than it is. Also, I agree with those who say you can't just dive into this wave and survive it, because it doesn't simply pass over your head. The energy goes from the surface to the bottom, and by the time it has gotten that close to shore, the water is a turbulent mess. Sadly, certain death except for a lucky few in freak incidents.