The phrase "devastating tsunami" describes a very powerful and destructive ocean wave. It implies that the wave was incredibly strong and caused widespread damage and destruction. Full definition
Ten years ago today, the most devastating tsunami in recorded history struck the Indian Ocean. (dotearth.blogs.nytimes.com)
2:50 p.m. Updated below with astounding video from Kesennuma, Japan Over the weekend, I mused on a question that's bothered me since I read Roger Bilham's report on the great earthquake and tsunami of March 11: Given the history of devastating tsunamis not far away, how could it have taken until 2006 for the word «tsunami» to show up in government guidelines related to the Fukushima nuclear complex? (dotearth.blogs.nytimes.com)
Massive debris flows below the waves can trigger devastating tsunamis, but sometimes they generate the merest ripple — now we know why (newscientist.com)