AGE, MAGNITUDE, AND CATASTROPHIC IMPACT OF POPOCATÉPETL’S EPICLASSIC (~A.D. 900) “PINK PUMICE” PLINIAN ERUPTION
The “Pink pumice” (PP) fallout was produced by Popocatépetl volcano during a Plinian (VEI=4-5) eruption ~ A.D. 900. It is part of a sequence that starts at the base with a few cm of laminated pyroclastic surge deposits followed by four distinct pumice fall units (P0, P1, P2, and P3) that are intercalated by pyroclastic flow deposits. Subsequently, these primary deposits became the source of lahars. The composition of the pumice varies insignificantly (SiO2 = 61 to 63 wt.%) with phenocrysts of plagioclase > orthopyroxene > clinopyroxene ± olivine ± opaques.
Sizes of lithics and isopach maps for each pumice fallout both indicate eruption columns that successively increased in height from ~21 km at the beginning of the eruption (P0) to 28 km toward the end (P3). The distribution of fallout shifted significantly from an initial dispersal axis towards the SW (P0) with a successive clockwise rotation to the NNE (P1), NE (P2) and finally to the E (P3). A total area of ~1000 km2 that includes pre-Hispanic settlements, was buried under >10 cm of pumice with a volume of ~0.5 km3 of dense rock equivalent (DRE). The short Plinian phase was followed by years of periodic flooding by massive rain lahars that affected ravines and large portions of the surrounding plains of Puebla. After the cataclysmic phase, a small dome filled the crater and produced small viscous lava flows that spilled shortly beyond the crater rim on the upper slope.
This eruption had a considerable impact on pre-Hispanic settlements, namely the large city of Cholula whose population exodus and relocation certainly had a long-lasting effect over areas far beyond the volcano.