How can a earthquake form a tsunami?

Ordinary waves affect the surface layer of ocean water, usually no deeper than several meters. Also, ordinary waves don't move much water, but for the most part just shift relatively small volumes of water alternately ahead and back. Tsunamis are different, because the triggering earthquake causes a massive shift of the entire column of water, from the surface to the ocean floor. This is why tsunamis are so powerful and so destructive. A huge quantity of water washes forward. And if it seems to you that water in general is so 'soft and giving', and you wonder how it can be so destructive, then stop to think that one cubic meter of plain water (very close to one cubic yard) weighs in at very close to one ton. One ton; two thousand pounds. If you have a meter stick or yardstick handy, you can very quickly imagine (or even make) a cubic meter/yard. How fast would one ton of water have to be moving in order to cause some damage? Next time you're watching the surf roll in at the beach, imagine how many tons of water you are looking at.