Geology and radiocarbon ages of Tláloc, Tlacotenco, Cuauhtzin, Hijo del Cuauhtzin, Teuhtli, and Ocusacayo monogenetic volcanoes in the central part of the Sierra Chichinautzin, México

Tláloc, Tlacotenco, Cuauhtzin, Hijo del Cuauhtzin, Teuhtli, and Ocusacayo monogenetic volcanoes located within the Sierra del Chichinautzin Volcanic Field (SCVF) at the southern margin of Mexico City were studied to further refine attendant volcanic hazards in this heavily populated region. Based on fieldwork and Landsat imagery interpretation, a geologic map was produced, morphometric parameters characterizing the cones and lava flows were determined, and the areal extent and volumes of erupted products were estimated. The longest lava flow was produced by Tlacotenco and reached 9.5 km from its source; total areas covered by lava flows from each eruption range between 12.8 km2 (Tlacotenco) and 54.4 km2 (Tláloc); and total erupted volumes range between 0.26 and 1.36 km3 per volcano. Radiocarbon measurements of a paleosol underneath an ash layer from the Tláloc scoria cone yielded an age of 6200 years BP, while charcoal found within block-and-ash flow and lahar deposits from Cuauhtzin dome yielded ages of 7360 and 8225 years BP, respectively. The Tlacotenco dacite lava flow overlies Popocatépetl's Tutti Frutti Plinian pumice fall deposit dated at 14,000 years BP and is therefore younger than this prominent stratigraphic marker. On the other hand, Teuhtli and Hijo del Cuauhtzin scoria cones and the Ocusacayo andesite lava flows are overlain by the Tutti Frutti and therefore older than 14,000 years BP. These new dates together with other published dates for scoria cones in the SCVF imply that the previously determined recurrence interval during the Holocene for monogenetic eruptions in the SCVF of <1700 years [Siebe, C., Rodríguez-Lara, V., Schaaf, P., Abrams, M., 2004a. Radiocarbon ages of Holocene Pelado, Guespalapa, and Chichinautzin scoria cones, south of Mexico_City: implications for archaeology and future hazards. Bull. Volcanol. 66, 203-225.] needs to be corrected to <1250 years. This means that the time of quiescence since the last eruption of the SCVF (1670 years BP) exceeds that of the estimated recurrence interval during the Holocene.