Tsunami: the waves generated by a sudden upward or downward movement of a large area of the seafloor or by an asteroid impact. Causes of tsunami include subduction earthquakes, collapse of the flank of a volcano, large landslides, and asteroid impacts. Catastrophe in the indian ocean y december 2004, 230,000 people killed in costal areas around indian ocean y caused by 9. 1 earthquake just off the indonesian island of sumatra y. The movement of this fault displaces the entire mass of overlying water and produced a series of waves that moved rapidly away from the seafloor. Tsunami are less common in indian ocean as pacific ocean y y need for effective warning systems y emergency procedures are needed y earthquake and tsunami educated is needed for coastal areas. Large landslide that fall from mountains and into a large body of water can generate tsunami. Less common that earthquake generated or landslide generated.