A ~31 ka Plinian-subplinian eruption at Tláloc Volcano, Sierra Nevada, Mexico

Tláloc volcano (19°24`40"N; 98°42`48"W; 4,120 m.a.s.l.) is a Pliocene-Pleistocene stratovolcano located NE of México City, Mexico. It represents the northernmost volcano of the N-S Sierra Nevada Range, which consists of Tláloc-Telapón, Téyotl, Iztaccíhuatl, and Popocatépetl volcanoes. Tláloc has always been considered the oldest (and extinct) volcano of the Sierra Nevada Range, although no detailed studies had been carried out. Recent field data has revealed important new information about its eruptive history, including a large magnitude Plinian-subplinian eruption, here referred to as the Multilayered White Pumice (MWP). This eruption started with a continuous yet unstable eruptive column that reached the stratosphere, which deposited several pumice-rich horizons that total 1 m at a distance of 12 km from the volcano. A preliminary isopach map of the deposit indicates that these fall layers were distributed mainly to the north-northeast, and encompass a minimum area of 120 km2 around the volcano. The event ended with total collapse of the eruptive column, which produced four, pumice-rich pyroclastic flows dispersed on the N and E slopes of the volcano. Those flow deposits fill gullies up to 25 m in thickness, at a distance of 12 km from the vent. The deposits are massive matrix-supported layers consisting of block-size fibrous rhyolitic pumice set in an ashy matrix rich in quartz and biotite crystals. Pumice clasts contain phenocrysts of K- feldspar, quartz, biotite, and Fe-Ti oxides. Charred logs are common, and charcoal from those logs yield an age of 31,490 +1995/-1595 years BP. So far, the MWP is the youngest dated deposit of Tláloc Volcano. Our results call into question the widespread idea of a N-S migration of the volcanism in the Sierra Nevada, beginning with the formation of Tláloc volcano and ending with the active Popocatépetl volcano.