Landslides can cause disasters by moving rocks from slight ground movements driven by gravity along with other factors. An earthquake in Napier, New Zealand on February 3, 1931 at 10:30 am killed 256 people and seriously injured 365, and was believed to be a major aftershock from an earthquake in Australia. Tsunamis, also called harbor or tidal waves, can vary in size and height, with those over 20 meters having only a 5% chance of survival.