Facebook was founded in early 2004
- the year the tsunami hit - but it wasn't open to the general public at the time. Twitter didn't come into existence until 2006. And part of the inspiration for YouTube came when a founder was looking for online videos of the tsunami - and couldn't find them.
So what might the reaction to the tsunami have looked like on today's social media? We asked the audience of the BBC's Indonesian Service to tweet messages as if they had gone back in time to 26 Dec 2004.