The following have at various times been associated with a tsunami:
- An earthquake may be felt.
- Large quantities of gas may bubble to the water surface and make the sea look as if it is boiling.
- The water in the waves may be unusually hot.
- The water may smell of rotten eggs (hydrogen sulfide) or of petrol or oil.
- The water may sting the skin.
- A thunderous boom may be heard followed by
- a roaring noise as of a jet plane
- or a noise akin to the periodic whop-whop of a helicopter,
- or a whistling sound.
- The sea may recede to a considerable distance.
- A flash of red light might be seen near the horizon.