AN EXCEPTIONALLY WIDESPREAD IGNIMBRITE WITH IMPLICATIONS FOR PYROCLASTIC FLOW EMPLACEMENT

PUMICE-rich pyroclastic flows leave deposits called ignimbrites(1), wh ich are common in the eruption records of are and intracontinental vol canoes(2,3). Pyroclastic flows represent the most dangerous manifestat ion of volcanism(4) because of their volumes, rapid emplacement at hig h temperatures, and capacity to extend >100 km from the source. Howeve r, maximum distances travelled and extents of areas destroyed by pyroc lastic flows remain poorly known. Historic examples have been relative ly small, the largest reaching to only similar to 35 km from the vent( 5), but prehistoric ignimbrites over 150 km across are known(3,6-10). The largest ignimbrites are invariably partly buried or eroded, and on ly minimum estimates of their size (and hence of their destructive cap acity) can be made. Here we describe the similar to 1-Myr-old Kidnappe rs ignimbrite, erupted from the Taupo Volcanic Zone in New Zealand, wh ich we have correlated for greater than or equal to 385 km and which t hus represents the most widespread ignimbrite yet known, We suggest th at this wide distribution primarily reflects a coupling of high initia l flow velocities with large mass fluxes, and that favourable flow pat hs and emplacement of flows over a wet substrate may have aided their mobility.