The ignimbrite flare-up
Western North America is buried under repeated supereruptions as the subducting slab rolls back.
- When
- —
- Duration
- 8.9 million years
- Known to
- ± 2 million years
- Era
- Oligocene, Cenozoic
Between roughly 36 and 25 million years ago the western United States and Mexico experience one of the most intense episodes of explosive volcanism in the geological record, producing hundreds of calderas and ash-flow sheets from Colorado to the Sierra Madre Occidental. The trigger is the foundering and rollback of the flat Farallon slab that had driven the Laramide orogeny, letting hot asthenosphere flood in beneath thick continental crust. The ash blankets are what bury and preserve the mammal faunas of the western badlands.