Christmas in 2004, a 9.1 magnitude earthquake triggered tsunami waves that killed some 230,000 people across a dozen countries.

On Dec. 26, 2004, in one of the worst natural disasters of the modern era, a 9.1 magnitude earthquake spurred catastrophic waves that brought destruction and devastation to at least 12 countries. It left some 230,000 people dead, and some 1.7 million more were displaced — hitting India, Indonesia, Sri Lanka, and Thailand the hardest.

The powerful 9.1-magnitude earthquake off the coast of the Indonesian island of Sumatra, triggered a tsunami that killed around 230,000 people across a dozen countries.

Survivors and families of victims visited mass graves, lit candles and comforted one another across Southeast and South Asia in ceremonies to mark the disaster that killed some 230,000 people.

The brunt of the tsunami was felt in the Indonesian province of Aceh, where 170,000 people perished. Sri Lanka, India and Thailand were devastated, too. More than a thousand miles apart, across the Indian Ocean, hundreds of coastal communities were united in their grief, and in facing years of rebuilding and regrouping.

Understanding of the Sumatran subduction zone and its hazards has increased since the 2004 Indian Ocean earthquake and tsunami.

The Asian tsunami that crashed into coastal communities around the Indian Ocean on Dec. 26, 2004, is this century’s deadliest natural disaster so far.

Emotional ceremonies were expected across Asia on Thursday to remember the 220,000 people who died two decades ago when a tsunami devastated coastal areas around the Indian Ocean, in one of the worst natural disasters in human history.