My favorite Big, Dumb Disaster Movies:
Backdraft (1991) - I'm not sure I consider this to be a disaster movie, but I do see it mentioned on these lists once in a while. If we're gonna call it a disaster movie, I'm definitely putting it on my list. But if not, that's okay. Regardless, if you ever need a jolt of testosterone without all the violence, this movie will grow you a whole mustache.
The Core (2003)
Dante's Peak (1997)
The Day After Tomorrow (2004)
Outbreak (1995)
The Towering Inferno (1974) - I think this is probably the movie that set me on my lifelong path of destruction.
Twister (1996)
Volcano (1997)
My favorite Legit-Good Disaster Movies:
Children of Men (2006) - Unlike Backdraft and Take Shelter, below, I almost never see this mentioned in lists of disaster movies, and it's not because people didn't like it. Go figure.
The China Syndrome (1979)
Cloverfield (2008) - Why this and not other kaiju movies? Because the protagonists never fight the monster. They just scream and run and die. Even in the scenes where our heroes see the Army fighting back, it's not stirring or invigorating, it's still just terrifying and our heroes do what most of us would do and keep running. It's also a parable (fable?) about 9/11, so in that sense you could say it's about terrorism, and I'm not including any other movies about terrorism. I wouldn't stop you from calling this an alien invasion movie, and I haven't got any of those here, either. So, okay, if for any of those reasons you want to strike this from your list of disaster movies, I won't hold it against you.
Contagion (2011)
Deep Impact (1998)
Greenland (2020)
Hours (2013) - Not to be confused with The Hours. Heh.
The Last Days / Los últimos días (2013)
The Poseidon Adventure (1972)
Take Shelter (2011) - Like Backdraft, I don't know if I really think of this as a disaster movie, but I see it referred to that way sometimes. If it's gonna be called a disaster movie, I have to have it here. If not, that's fine, it'll show up on other lists.
These Final Hours (2013)
The Wave / Bølgen (2015)
I know I'm forgetting some. I also decided that disastrous events that affect only a small number of people are Survival Movies, and constitute a whole separate list. Apollo 13; The Martian; Castaway; etc.