Survivors Mark 20 Years Since World’s Deadliest Tsunami with Ceremonies at Places Devastated by the 2004 Tragedy

Thousands gathered in mourning on Thursday, Dec. 26, to mark two decades since the world’s largest tsunami.

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.

At mass graves throughout Indonesia’s Aceh province on Thursday, people gathered and prayed to honor victims of the tragedy, The Associated Press reported. At one in Ulee Lheue village, where 14,000 unidentified victims are buried, families of those killed by the tsunami wept and placed flowers.

There were similar memorial ceremonies in Ban Nam Khem, a small fishing town in Thailand that was among those most devastated by the tsunami in the country, as well Chennai, India, and Pereliya, Sri Lanka, the AP reported.

Louis Mullan and his younger brother, Theo, were only teenagers when the tsunami destroyed Khao Luk, Thailand, where their family was on vacation, killing their parents.

The boys flew back to Cornwall, England, a week after the storm as orphans. But when they arrived home, they received an unexpected message from a neighboring family of four offering to take them in, Louis told PEOPLE in November.

“She felt something was telling her that she had to do that,” Louis said of the mom that suggested she take them in. “If we didn’t have that, I think that’s when it would’ve been so much harder.”

He added, “The opportunities they’ve offered us and the love that they’ve given us has made us who we are.”

For Rachel Hearson, it was a “pocket of air” that saved her life as the storm slammed the Phi Phi Islands in Thailand, where she was on holiday, she told PEOPLE last month. Hearson, now 61, was rescued by a small fishing boat before she went back to land to look for her partner, Cici Romain, who she eventually found amid the wreckage helping others. 

Though she didn’t have any formal medical training, she held the hands of the survivors as they waited for the rescue helicopters. Two decades later, she said she’s given up her career as a fashion designer to instead work for a cancer charity — learning from the tragedy, “I can be there for other people if I’m needed.”

“Maybe it’s hard [for the younger generation] to understand,” Soffie Modin, another survivor of the tsunami, told PEOPLE. Modin was also on vacation on the Phi Phi Islands and required eight months of hospital and home care to recover from an injury to her leg. While she survived, her then-fiancé’s brother was killed in the disaster.

Modin is one of the many survivors who appears in National Geographic’s Tsunami: Race Against Time, a powerful four-part docuseries that sheds light on the bravery and heroism by the survivors of the disaster.

“It’s a little bit nice to just lift that lid again,” Modin told PEOPLE about her participation in the docuseries, noting the necessity for new generations to learn about the tragedy.