I'm pretty sure that prehistoric Britain was scoured by a landslide-generated Mega Tsunami. I agree that it's impossible to be prepared for everything. I think it makes sense to devote most of one's resources- personally and as a society- to the most likely and/or serious threats. Let's face it- if the Yellowstone Caldera explodes in a full force eruption there's not much we can do. That would be a very challenging event for humans a species, much less individual people. [While the media likes to talk about how "overdue" such an explosion is the fact remains that the best geological evidence points to decreasing activity over the millenia- ie. it may not be overdue so much as just slowing in activity.] On the other hand, earthquakes, tsunamis and hurricanes/typhoons are much more regular occurrences. Add to this list tornadoes, flood and blizzards and you're getting down to the things that we really should be preparing for.