A newly discovered, large volume (3.3 km3) volcanic debris-avalanche is described from the Pirongia Volcano in North Island, New Zealand. Mapping, field surveys and drill core data were used to reconstruct the distribution and facies of the deposit (the Oparau breccia). The debris avalanche was channelised into a lowland graben structure resulting in a prolonged runout distance of ≥20 km and substantial thickness of >200 m in medial areas. The deposit contains block and matrix facies dominated by ankaramite basalt sampled from the oldest parts of the volcanic edifice. The age of deposition of the Oparau breccia is constrained to the period 2.2-1.75 Ma. The collapse source zone is marked by a prominent unconformity on the southwestern flank of the mountain. Movement on faults within the graben is identified as the most likely cause of sector collapse. The collapse scarp is infilled by 5 km3 of post-collapse volcanic material.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5505549
El Campo Volcánico Xalapa (CVX) consta de 42 conos de escoria y al menos 2 volcanes escudos, cuyas edades varían entre 2 millones de años (M.a.) hasta 870 años (a) antes del presente (datos radiométricos publicados). Mediante la determinación de los parámetros morfométricos, se estimaron las edades relativas de los conos de escoria (tipo de volcán predominante en el CVX) aun no fechados. La densidad de los conos de escoria dentro del campo varia de 0 hasta 2 por km2. El uso de la función kernel permite identificar zonas con mayor densidad de volcanes al NW de Xalapa entre Acajete y Las Vigas de Ramírez (grupo La Joya) y al norte de Coacoatzintla, mientras zonas con concentraciones menores están localizadas alrededor de Pacho Viejo y al norte de Ayahualulco. Aunque el Campo Volcánico Xalapa no es el campo con mayor número de edificios del Cinturón Volcánico Trans-Mexicano (CVTM), ni el más denso; sin embargo se debe crear consciencia de que puede dar lugar al nacimiento de un nuevo volcán en el futuro. Un monitoreo sería deseable.Palabras clave: Campo volcánico Xalapa; conos de escoria; volcanes escudo; volcanes; parámetros morfométricosAbstractThe Xalapa Monogenetic Volcanic Field (XMVF) defines a group of 42 scoria cones and at least two lava shields that erupted between 2 million and 870 years before present (according to published radiometric data). In this study, we measured the morphometric parameters of XMVF scoria cones in order to assign relative ages to undated volcanic centers. The density of vents within the limits of the volcanic field (estimated by using spatial point density analysis) and found to vary from 0 to a maximum of 2 volcanoes per square kilometer. Kernel density function analysis revealed that the highest concentrations of volcanoes occur NW of Xalapa between Acajete and Las Vigas de Ramirez (La Joya group), and N of Coacoatzintla, while lesser concentrations occur around Pacho Viejo and to the N of Ayahualulco. Although the XMVF is relatively small and has a low vent-density compared to other volcanic fields in the Trans-Mexican Volcanic Belt, a greater level of public awareness and hazard monitoring, is required in preparation for the next XMVF eruption.Keywords: Xalapa Monogenetic Volcanic Field; scoria cones; lava shields; volcanoes; morphometric parameters
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.