>like a tsunami?<

Not in my mental imagery anyway! As far as I'm concerned a tsunami rolls forward and up over the land. Waterfalls fall down, not up (except if you've just been thinking about Escher and perpetual flow machines, but that's another thread...)

However, I will concede a tsunami may have made its way outward from the area around the base of the waterfall! So perhaps there was a waterfall AND a tsunami.

(or is that 'perhaps there were a waterfall and a tsunami'? Neither sounds correct any more. At least I'm in a good place to ask for help! )