[Condor51]

The media is saying the tidal wave is only 20 feet tall. I can't understand how a 20 foot wave can cause this much loss of life and property.

Uh maybe because Asians are 'little' people.

Ok seriously... the force contained in a wall of water 20 Feet High is .. technically speaking .. 'humongous'.

It's that physics thing, Newton's 2nd law; F=ma (force = mass x acceleration)
Remember one gallon of water weighs is 8.345lbs and a cubic foot of water weighs 62.428lbs. And the speed of this tidal wave has been estimated at 500MPH. Do the math and it's self explanatory.

[Uncledave]

And the speed of this tidal wave has been estimated at 500MPH. Do the math and it's self explanatory.

That can be the speed deep at sea, where the wave may only be a couple of inches high, but many miles wide. As it approaches the shallower shore the speed drops sharply but the height spikes in proportion.

[Jorge]

And the speed of this tidal wave has been estimated at 500MPH. Do the math and it's self explanatory.

Actually the speed of a tidal wave can reach hundreds of mph ONLY in the open ocean.
When they build height and hit land they have slowed down considerably.