• A tsunami is a series of waves with a long wavelength and period (time between crests). Time between crests of the wave can vary from a few minutes to over an hour. • Tsunamis are often incorrectly called tidal waves; they have no relation to the daily ocean tides. • Tsunami (soo-NAH-mee) is a Japanese word meaning harbour wave. • Tsunamis can occur at any time of day or night.