What ‘supervolcano’ actually means
USGS uses the term for volcanic centres that have produced magnitude-8 eruptions, involving more than about 1,000 cubic kilometres of erupted material. Yellowstone has produced giant caldera-forming eruptions in its geological past.
What the worst case would do
A future giant eruption could devastate the nearby region with pyroclastic flows, spread ash across large parts of North America and perturb global climate for years.
Why ‘overdue’ is misleading
Volcanoes do not erupt on a timetable. Yellowstone’s past intervals are not regular enough to turn an average recurrence time into a countdown, and USGS reports no evidence that a catastrophic eruption is imminent.
What monitoring would see
The Yellowstone Volcano Observatory tracks earthquakes, ground deformation, gas and thermal activity. Scientists expect a truly giant eruption to be preceded by intense, widespread unrest far above normal background levels.
Research record
USGS Yellowstone — Questions About SupervolcanoesOfficial · open sourceUSGS — What would happen in another Yellowstone supereruption?Official · open sourceUSGS — No, Yellowstone isn’t going to wipe out humanityOfficial · open sourceCould Yellowstone End Civilisation?
Direct answer: Yellowstone could cause a global-scale disaster in an extreme future eruption, but it is not ‘overdue’, there is no evidence a supereruption is imminent, and such an event would not automatically mean human extinction.
High-consequence, extremely low-probability hazard. The evidence supports monitoring and preparedness, not countdown narratives.