Which was the deadliest tsunami in recorded history?

The deadliest tsunami in recorded history was the 2004 Indian Ocean tsunami, which killed almost 230,000 people in fourteen countries including Indonesia, Sri Lanka, India, Thailand, Somalia, Myanmar, Maldives, Malaysia, Tanzania, Seychelles, Bangladesh, South Africa, Yemen and Kenya (listed in order of confirmed death numbers).

The 2004 Indian Ocean earthquake and tsunami (also known as the Boxing Day Tsunami and, by the scientific community, the Sumatra–Andaman earthquake) occurred at 07:58:53 in local time (UTC+7) on 26 December, with an epicentre off the west coast of northern Sumatra, Indonesia. It was an undersea megathrust earthquake that registered a magnitude of 9.1–9.3 Mw, reaching a Mercalli intensity up to IX in certain areas. The earthquake was caused by a rupture along the fault between the Burma Plate and the Indian Plate.

A series of massive tsunami waves grew up to 30 m (100 ft) high once heading inland, after being created by the underwater seismic activity offshore.

Despite a delay of up to several hours between the earthquake and the impact of the tsunami, nearly all of the victims were taken by surprise. There were no tsunami warning systems in the Indian Ocean to detect tsunamis or to warn the general population living around the ocean. Tsunami detection is not easy because while a tsunami is in deep water, it has little height and a network of sensors is needed to detect it.