Review of geology and geomorphology of the Xalapa Monogenetic Volcanic Field, eastern Trans-Mexican Volcanic Belt

Abstract

Monogenetic volcanic fields have associated volcanic hazards that are not always well constrained due to the lack of complete and well established geological and geomorphological studies, field boundaries, volcano inventories, and of detailed reconstruction of individual volcano eruptive histories. This work presents a detailed review and further insights into geology and geomorphology of the Xalapa Monogenetic Volcanic Field (XMVF), achieved by completing a comprehensive revision of all previous works on the XMVF, along with new data produced from extensive fieldwork, field and digital mapping, radiocarbon dating, and morphometric and density analyses. The main results are: (i) a renewed inventory of 72 XMVF monogenetic volcanoes - a total number larger than previously recorded (59); (ii) identification of six new and not previously identified monogenetic volcanoes: La Natividad, La Pedrera, El Puente, Rancho Sicomoro, and Puentecillas scoria cones, and the Tenampa maar; (iii) recognition of four possible new volcanoes integrating the Macuiltépetl cluster, recorded in historical documents; (iv) corrections and new volcanoes identified in the volcano clusters of Pextlan, La Joya, Ocotepec, and Cruz Negra; (v) geological mapping of all lava flows associated with the 72 monogenetic volcanoes; (vi) comprehensive morphometric analyses of all 72 reported volcanoes; (vii) three new radiocarbon ages corresponding to 780 ± 60 BP and 1340 ± 60 BP lava flows of El Volcancillo scoria cone, and to 1300 ± 60 BP and 1115 ± 80 BP lavas of La Pedrera volcano; (viii) new evidence of the late Pleistocene to Holocene age of the Acatlán scoria cone; (ix) new outline of the boundaries of the XMVF based on fieldwork and remote sensing; and (x) volcanoes and lava flows density and distribution maps. From these results, we conclude that, in case of renewed monogenetic activity in the XMVF, the most likely deterministic hazard model would comprise effusion of lavas of variable length (3–40 km), of up to extremely long tube-fed pahoehoe lava flows; explosive activity ranging from typical to violent Strombolian style eruptions producing scoria cones, extensive fallouts, and associated pyroclastic density currents; and phreatomagmatic style activity producing maars, tuff rings and/or tuff cones, and sequences of wet pyroclastic density currents. Hazard distributions in these scenarios would be mainly controlled by topography, local tectonics, groundwater level and basement rocks lithology, and would mostly affect the north and south flanks of Cofre de Perote volcano, as well as central XMVF sectors where the metropolitan area of the city of Xalapa and towns of Naolinco and Acatlán locate. From this review, we conclude that without any further studies of geology and chemistry of every single volcano, the western boundaries of the XMVF will remain unclear, and the associated volcanic risk will remain underestimated. This work provides a fundamental basis from which further and more detailed work could be attained.