The violent Strombolian eruption of 10 ka Pelado shield volcano, Sierra Chichinautzin, Central Mexico

Abstract

Pelado volcano is a typical example of an andesitic Mexican shield with a summital scoria cone. It erupted ca. 10 ka in the central part of an elevated plateau in what is today the southern part of Mexico City. The volcano forms a roughly circular, 10-km wide lava shield with two summital cones, surrounded by up to 2.7-m thick tephra deposits preserved up to a distance of 3 km beyond the shield. New cartographic, stratigraphic, granulometric, and componentry data indicate that Pelado volcano was the product of a single, continuous eruption marked by three stages. In the early stage, a > 1.5-km long fissure opened and was active with mild explosive activity. Intermediate and late stages were mostly effusive and associated with the formation of a 250-m high lava shield. Nevertheless, during these stages, the emission of lava alternated and/or coexisted with highly explosive events that deposited a widespread tephra blanket. In the intermediate stage, multiple vents were active along the fissure, but activity was centered at the main cone during the late stage. The final activity was purely effusive. The volcano emitted > 0.9 km3 dense-rock equivalent (DRE) of tephra and up to 5.6 km3 DRE of lavas. Pelado shares various features with documented “violent Strombolian” eruptions, including a high fragmentation index, large dispersal area, occurrence of plate tephra, high eruptive column, and simultaneous explosive and effusive activity. Our results suggest that the associated hazards (mostly tephra fallout and emplacement of lava) would seriously affect areas located up to 25 km from the vent for fallout and 5 km from the vent for lava, an important issue for large cities built near or on potentially active zones, such as Mexico City.