People are gathering in prayer and visiting mass graves in Indonesia’s Aceh province to mark 20 years since the massive Indian Ocean tsunami, one of modern history’s worst natural disasters

Christmas in 2004, a 9.1 magnitude earthquake triggered tsunami waves that killed some 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.