I think there are buoys that are strategically placed to warn of an incoming tsunami. (Perhaps they should be checked as often as smoke detectors in a house to make sure they are still working.) Volcanos? A dramatic rumbling noise and shaking of the ground should tell you that perhaps something is going to happen, especially if it is coming from out of the cone. A growing bulge at the side of a mountain seen from a distance of a mile or more should also be a sign that perhaps one might consider moving out--preferably within the next half hour or sooner.