Actually, it has been strengthened of late by the major collapse that happened in Alaska back in the 50's, I think, which produced a wave several hundred feet high in an islet and out to the ocean. Swiss researchers are doing experiments to understand the 'collapse' phenomenon better.
Nope. It hasn't. I suspect you don't read the Journal of Tsunami research.
The Lituya Bay eruption has very little to do with what (basically one guy) was claiming about La Palma (and frankly I think the frenzied media attention went to his head.)
Landslide Tsunami have difficulty propagating great distances - unlike earthquake tsunami. It's one thing to project a big local tsunami, another to project a teletsunami.
If you're only getting your science info from the MSM, you're not getting good info. They only want to report the exciting and the dangerous. You have to read scientific journals directly.
http://www.drgeorgepc.com/TsunamiMegaEvaluation.html
A good article about the collapse megatsunami threat....
There are some serious problems with the modeling of the La Palma waves...and this guy isn't the only guy that has pointed this out...
But the media (And crappy cable science documentaries) consistently ignore the doubters and present a sensationalized one-sided story.