I guess the peak moment (if you'll excuse the pun) for a good volcano apocalypse story in the U.S. would've been May-July 1980. Or possibly early 1997. But I bet bad movies aren't as effective.

Interesting. A couple thoughts:

Are the general public more afraid of comets/asteroids/meteors hitting the Earth, or of volcanoes? Maybe it depends on where they live -- you can count on the meteor causing worldwide devastation (at least if it's a movie), while the volcano is more localized. (But you noted that even people who live near one may not care, so maybe not.) But even if those two volcano movies Jon pointed two were pretty much flops, the fact that they got made suggested that someone thought the idea would appeal to audiences.

Have there been any Big Quake movies? Maybe in California people are in too much denial to want to see one, and elsewhere in the US it's too unlikely?

I thought Mary Rosenblum's "drylands" stories were really good (and her followup novel fairly good), and she once told me that her research suggested that the drying up of the Pacific Northwest was very plausible. Those stories got a certain amount of attention, but more (I think) for the characters and situations than for playing on people's Post-Disaster fears. So I think you can write a good story about such a situation, it's just not necessarily going to turn into a blockbuster unless it already matches the zeitgeist. (Well, and not necessarily even then, of course.)