A tsunami in the Indian Ocean on 26 December 2004 that killed an estimated 230,000 people. It was caused by an undersea earthquake measuring 9.0 on the Richter scale off the north-western coast of Sumatra. Tsunamis in the Indian Ocean are comparatively rare and there was no warning system in place; the 2004 tsunami therefore struck largely without warning on coastlines that had not been evacuated. Indonesia and Sri Lanka suffered the highest casualties, with probable death tolls of 168,000 and 35,000 respectively. The economic damage was equally severe: in Indonesia it amounted to about $4.5 billion and in Sri Lanka, about $1.5 billion. The 2004 tsunami was the most destructive tsunami on record and possibly the most destructive natural disaster of any kind.