The worst tsunami in history happened 20 years ago. Here's how it unfolded

The 2004 Indian Ocean tsunami was one of the most severe natural disasters in human history. This catastrophic event brought devastating blows to multiple countries, resulting in immense loss of life and property damage. The scale of the disaster underscored the vulnerability of coastal communities and the need for improved disaster preparedness.

On December 26, 2004, at 7:58 AM local time, a powerful earthquake with a magnitude of at least 9.1 struck the Indian Ocean near the northern coast of Sumatra, Indonesia. Within 15 minutes, the tsunami began to hit the coasts of northern Sumatra and the Nicobar Islands, according to data from the Australian Institute for Disaster Resilience. Approximately two hours later, the tsunami reached Sri Lanka, India, and Thailand. About seven hours later, the waves even impacted Mauritius and the east coast of Africa.

The U.S. National Oceanic and Atmospheric Administration estimated that waves reached heights of up to 51 meters in Aceh province, northern Sumatra, Indonesia. These waves were approximately 30 times the height of an average Australian person and seven times the height of a two-story building. The tsunami caused the deaths of at least 227,000 people in over a dozen countries from Indonesia to the coast of Africa, with Indonesia, Sri Lanka, Thailand, and India being the most severely affected.

The Australian Institute for Disaster Resilience called it the worst tsunami in history and one of the ten largest earthquakes ever recorded. Dr. John Dawson, Community Safety Leader at Geoscience Australia, stated, "It is undoubtedly the tsunami that has caused the largest number of deaths, dating back to historical records from 365 AD." He also pointed out, "What stands out to me is the large number of people who died a long way from where the earthquake occurred. Over 52,000 people died more than 1,000 kilometers from the earthquake, which is unusual in disasters."

Dawson stated that earthquakes of this magnitude are very rare, with the only recent earthquake of similar scale being the one that occurred in the Tohoku region of Japan in 2011, which triggered the Fukushima nuclear disaster. He added, "In 2004, there was no tsunami warning capability in the Indian Ocean, so the region was unaware of it, which is one of the reasons why so many deaths occurred—the waves arrived without warning." Since the Indian Ocean earthquake, Geoscience Australia and the Bureau of Meteorology have been working together to monitor earthquakes and potential tsunamis. On the 20th anniversary, they hope people will not forget this event. "The risk with very rare but catastrophic events is that it gradually fades from people's memory, and people forget," Dawson said. "That's why it's important to reflect on the events of 2004 and say this could happen again. Are our communities prepared for it?"