We have a dormant volcanic formation at the East end of Lake Superior. There's another one in the vicinity of Martinsville and Baden Springs Indiana. I know of one that's still chemically different enough on the top to show up as a large round zone just Souf' of Seymour, Indiana.
Those things are dormant just like the one in Reston, Virginia is dormant.
I don't expect them to blow up any time soon BUT..... (heavy drums beating in the background) .... it's a lot easier to get them to do that than most folks imagined.
BTW, there's one at the confluence of the Rhine and Mein rivers in Deutschland. Even has some still extant vents. It has gone off a time or two since the disappearance of the Eur-Asian ice!