While it's true that the Yellowstone caldera is a massive, hidden "supervolcano" of sorts, it only blows about once every 600,000 years or so.
Present-day predictions that say Yellowstone is going to blow in the next 70 or 80 years are based on pure hokum. There's no geological evidence whatsoever that indicates a blowing of the caldera is going to happen any time soon.
Yes, it's true that once Yellowstone does blow, it will blanket the atmosphere with ash and cause mass global starvation, likely collapsing the human population by 80% or so. It will be catastrophic... but it's extremely unlikely to happen in our lifetimes.
You'd be much better off focusing on global events that are realistically likely to occur in the next few years or decades: Global debt collapse, cyberwar grid collapse, EMP nuclear weapons, acts of war, etc.
There is an outside chance, by the way, that someone could detonate a nuclear bomb in the ground inside Yellowstone and possibly set off the caldera... but the last time I was in Yellowstone, there was a massive body of water (a lake) over the caldera, making such an attempted act of eco-terrorism virtually impossible to carry out.
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