Caused by an earthquake on an ocean's bed, a tsunami is one of the deadliest and most destructive natural disasters on Earth. The flooding and associated effects of the tsunami that started in the Indian Ocean in December, 2004 caused the deaths of an estimated 300,000 to 500,000 people across several countries, including India and Indonesia.
The most direct impact of a tsunami is the massive flooding it produces along coastlines of affected areas. Huge walls of water gush onto the land. Because of their erratic sources, tsunami are much more difficult to predict and prepare for than other natural disasters such as hurricanes. People in the path of the rushing water drown, and buildings and trees get carried away.
Tsunamis also have a cumulative effect on the Earth, as well. Universe Today indicated that the 2004 Indian Ocean tsunami sped up the Earth's rotation and caused vibrations all across the Earth's surface.
In some cases, the residual effects of standing water left after a tsunami are the most impacting. Water often creeps several miles inland and sits for days, weeks or months, becoming stagnant over time. People who survive the initial onslaught are at risk of illness and disease triggered by the bacteria and contaminants in the flooded waters. Treating the injured and redeveloping affected areas can also cost billions of dollars.