I feel the supervolcanic eruption was sped up by someone. As all the scientists seemed in shock how fast it happened without warning. Kane and Sinatra might of got bored of waiting for it to happen naturally, or thought if it happened earlier it would cause more panic within the Supreme Court/Congress/Joint Chiefs of Staff as without them around controlling their new underground city would be more easy, and then they be the most powerful people down there.
With Episode 8 being called "The Man Who Kept the Secrets" I sense this going to be Kane Bradford.
His secrets will be how him and Sinatra caused the end of the world, Kane was famous for drilling for oil.
What if this skill came in handy to be able to push the timetable of the eruption?!