7.9 Quake off Tonga

[Alex]

Tsunami's out in open ocean (or deepening ocean) are generally only a few inches high. The energy of the shock wave only becomes seriously dangerous when the depth of the water rapidly declines (as when approaching land).

Haven't seen the pictures so don't know if that is relevant to the question at hand, though.

(Think of this way. You have enough power to an upward force of 7 million pounds. Which column of water will you lift higher: 20 feet or 2000?)