2004 - Tsunami
The earthquake occurred at sea, of the western coast of Northern Sumatra, but the subsequent tsunami affected the countries all around the Indian Ocean, including Indonesia, Sri Lanka, India, Thailand, and even as far as the coastal countries of Eastern Africa. For many there was no hint of the incoming disaster until the waves hit the coastline. Nearly 230,000 people were lost, either confirmed dead or still missing, and the 2004 tsunami has been labeled as the worst recorded natural disaster in terms of lives lost.
Tsunami page from the US Geological Survey
Kyoto (Japan) University's Disaster Prevention Research Institute