Good points, Chris. I also saw a (the same?) video of the Indonesian tsunami hitting a resort and noted then that the face of the wave did seem to have a rather sheer face just as it came onshore. But it was nowhere near 30m in height, there.

And you also brought out the point that, in oceanography, wave heights are usually measured trough-to-crest. But I'm not sure how that would work with tsunami where their troughs must be curtailed significantly by the shallow depths where they come ashore. I know that causes the crest to rise, but it seems that there would no longer be a true trough. As in shallow bays which empty preceding the arrival of a tsunami. The sea-bottom does not represent the level of the trough.

Mike W.