[Velveeta]

The tsunmi waves could last up to six hours.

I had no idea that tsumani waves could last that long.

[Godzilla]

I had no idea that tsumani waves could last that long.

First, tsumani waves are long period, not short period like normal waves. The wave just keeps rising after the front part of the wave crashes in. Longer warning periods deal with reflections of the wave from across the basin.