Yep, there's lots of smaller thematic social media collections in university or community archives. There was a new one for Brexit I saw doing the rounds on archivist circles on Twitter last week. There's also a couple of them for BlackLivesMatter. I can't think of any for Arab Spring to link you too off the top of my head but I'm sure there's more than one. I've built one from scratch before at an old job based on a campus controversy. Anything you're looking for in particular?

These are somewhat controversial among archivists and activists though, because they are built and collected without explicit consent, just the implicit consent that everything people put public on the Internet is "fair game." I don't really have a professional opinion on collecting this digital ephemera myself, but there are lots of people who have some robust opinions for and against it.