Is that correct..yes, icebergs float, but 90% of their mass is below the water line....( ask the Capt of the Titanic)..and the tidal wave is caused by the displacement of the water, right....?
The point was that the fall is slower in the case of ice: the chink may "slide" into the water, whereas this is not an option for rock.
Also, I have not read about tsunamis much, but my impression is that this is a shock wave (this is why it propagates much faster than the regular waves), so no permanent displacement of water is necessary.