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The Michoacán-Guanajuato volcanic field (MGVF) hosts >1,400 monogenetic structures younger than 5 Ma. Here we focus on the Malpaís de Zacapu Late Holocene cluster located in the western part of the Zacapu lacustrine basin, situated in the heart of native Purepecha province. The Malpaís de Zacapu comprises four distinct eruptions: the Infiernillo lava flow emitted at ~1450 b.c.; Malpaís Las Víboras, a purely effusive eruption at ~1000 b.c.; the Capaxtiro compound lava flow at ~150 b.c.; and the most recent eruption, the Malpaís Prieto lava flow at ~a.d. 900. Although these lava flows are not inhabited today, they were densely populated in pre-Hispanic times (before a.d. 1521), especially during the Milpillas phase (a.d. 1200–1450). Volcanological studies (geochemical studies and detailed mapping using high-resolution DEM from LiDAR) allowed us to characterize these eruptions in terms of their magma source (rock chemical composition, mineral assemblage), age (radiocarbon and paleomagnetic dating), magnitude and dynamics (volume, morphology of the deposits), as well as lava flow emplacement duration. The findings allow us to infer the potential impact that these eruptions had on the pre-Hispanic settlement history of the area.

The eruption of the c. 10 km 3 rhyolitic Las Derrumbadas twin domes about 2000 years ago generated a wide range of volcano-sedimentary deposits in the Serdán-Oriental lacustrine basin, Trans-Mexican Volcanic Belt. Some of these deposits have been quarried, creating excellent exposures. In this paper we describe the domes and related products and interpret their mode of formation, reconstructing the main phases of the eruption as well as syn- and post-eruptive erosional processes. After an initial phreatomagmatic phase that built a tuff ring, the domes grew as an upheaved plug, lifting a thick sedimentary pile from the basin floor. During uplift, the domes collapsed repeatedly to form a first generation of hetero-lithologic hummocky debris avalanche deposits. Subsequent dome growth produced a thick talus and pyroclastic density currents. Later, the hydrothermally altered over-steepened dome peaks fell to generate second-generation, mono-lithologic avalanches. Subsequently, small domes grew in the collapse scars. From the end of the main eruptive episode onwards, heavy rains remobilized parts of the dome carapaces and talus, depositing lahar aprons. The Las Derrumbadas domes are still an important source of sediments in the basin, and ongoing mass-wasting processes are associated with hazards that should be assessed, given their potential impact on nearby populations.

Volcanic signatures archived in polar ice sheets provide important opportunities to date and correlate ice-core records as well as to investigate the environmental impacts of eruptions. Only the geochemical characterization of volcanic ash (tephra) embedded in the ice strata can confirm the source of the eruption, however, and is a requisite if historical eruption ages are to be used as valid chronological checks on annual ice layer counting. Here we report the investigation of ash particles in a Greenland ice core that are associated with a volcanic sulfuric acid layer previously attributed to the 79 CE eruption of Vesuvius. Major and trace element composition of the particles indicates that the tephra does not derive from Vesuvius but most likely originates from an unidentified eruption in the Aleutian arc. Using ash dispersal modelling, we find that only an eruption large enough to include stratospheric injection is likely to account for the sizeable (24–85 μm) ash particles observed in the Greenland ice at this time. Despite its likely explosivity, this event does not appear to have triggered significant climate perturbations, unlike some other large extra-tropical eruptions. In light of a recent re-evaluation of the Greenland ice-core chronologies, our findings further challenge the previous dating of this volcanic event to 79 CE. We highlight the need for the revised Common Era ice-core chronology to be formally accepted by the wider ice-core and climate modelling communities in order to ensure robust age linkages to precisely dated historical and paleoclimate proxy records.

Scoria cones are abundant in most volcanic fields on Earth, such as the Michoacán-Guanajuato Volcanic Field, in the central-western sector of the Trans-Mexican Volcanic Belt. However, there are few in-depth studies on their eruptive style and controlling factors, despite of their diversity in shape and composition which implies a wide range of hazards. Here, we present results of morphologic, stratigraphic, sedimentary, petrographic, and geochemical studies of the prominent Las Cabras scoria cone located west of the Zacapu lacustrine basin in the center of the Michoacán-Guanajuato Volcanic Field. This basaltic andesitic to andesitic volcano formed between 27 and 26 kyrs BP on the steep slopes (>10º) of the lava shield of El Tule volcano. Over time, its dominant eruptive style changed from Strombolian to effusive. Initial explosive activity built a 170-m-high scoria cone and deposited thick tephra fallout on the surrounding sloping terrain. Structures in the deposits indicate that early friable fine-grained tephra underwent significant erosion due to syn-eruptive heavy rain coupled with the sloping nature of the underlying ground. This erosion generated lahars that very likely reached the Zacapu lake based on the pre-eruptive topography. As the explosivity dropped, lava was emitted from the base of the cone first to the S and SE, forming a thick, viscous lobe that filled a pre-existing E-W valley. The flow direction then deviated to the N and NE, to form thinner, less-viscous lobes fed from the vent by an open-channel. The lavas are covered by hummocks made of agglutinates and bombs that indicate that the eruption terminated by catastrophic collapse of the SE sector of the cone, possibly triggered by the intrusion of magma within the cone, which destabilized its downslope segment. The sudden flank failure was potentially associated with a late effusive event and the hummocks may have been carried away by the lava surge. Whole-rock chemical variations and crystal disequilibrium textures point toward a complex magma feeding system, involving mixing and mingling between different magma batches. This study shows that the formation of scoria cones on a terrain with a marked slope (>10°) has profound impacts on the eruption dynamics and related hazards due to its effect on cone stability and ash erosion. It also evidences the erosive effect of syn-eruptive rain on fine-grained tephra, especially when deposited on a slope. Finally, it reveals the complex magmatic processes that may occur in the shallow plumbing system of monogenetic andesitic volcanoes, which could be particularly important in inland areas of continental arcs.

International audience; Volcano sector collapses are catastrophic events that can mobilize huge volumes of material and cause changes in the magmatic plumbing system, leading to variations in growth rate and/or composition. Dating pre-historic volcanic debris avalanche deposits is challenging. Geological materials directly recording avalanche formation and amenable to radiometric dating are rare, and, in the case of Holocene events, the applicable radiometric dating techniques are scarce. Socompa volcano suffered the largest collapse event in the Central Volcanic Zone of the Andes, producing one of Earth's most spectacular and best-preserved volcano avalanche deposits. We apply multiple dating techniques to unravel the timing of Socompa's collapse and gain insights into its pre- and post-collapse eruptive history. The age of the collapse event is constrained by a 14C age of 6,200-6,400 BP of a paleosol buried by the avalanche, and by a post-collapse lava flow dated at 5.91 ± 0.43 ka by zircon double-dating. Bayesian age sequence modeling integrating these ages determines that the collapse occurred at 6.18-0.64+0.28 ka. Four zircon eruption dates and one unspiked K-Ar age between 69.2 ± 6.0 and 22.1 ± 1.9 ka constrain the age of the youngest stage of activity before the collapse. The ages, together with paleosurface modeling and volume calculations, allow estimating growth rates for the young pre-collapse and post-collapse stages of ~ 0.2-0.3 km3/kyr and ~ 0.5-2 km3/kyr, respectively, indicating a significant increase in activity after the collapse event. The collapse may have triggered a new growth phase or accelerated an ongoing one and was likely associated with a Plinian eruption that produced widespread pumice fallout. The pre- and post-collapse lavas have similar compositions and zircon crystallization age distributions, suggesting that the same or a similar magma reservoir was tapped before and after the collapse. Thus, huge collapses such as Socompa's event can promote increased volcanic activity as a consequence of the unloading effect, but the overall plumbing system may not be affected enough to show significant variations in erupted compositions, at least transiently. Our results highlight the efficacy of the zircon double-dating method for dating very young felsic lavas and for constraining the age of debris avalanche deposits. This is particularly relevant in the Andean Central Volcanic Zone and other regions with arid climates, where organic material is rare and hence 14C dating is often unfeasible. Furthermore, the post-collapse zircon eruption age of 5.91 ± 0.43 ka is the youngest radiometric age yet obtained for a lava flow in the southern Central Volcanic Zone, highlighting the youth of volcanic activity at Socompa, and confirming its status as a Holocene active volcano.

Simulating lava flows on a gentle slope is complex since they can propagate in a wide range of directions. It is an even greater challenge to define lava flow trajectories when an eruption lasts over several years and flows cool down, changing the surrounding topography. In this study, we test Q-LavHA, an open source plug-in that simulates lava flow inundation calculating its probability, and using Paricutin’s eruption (1943–1952) in central Mexico as a case study. We have appropriately calibrated the Q-LavHA plug-in for the Paricutin case study, which provides insights on how to better model lava flows in gentle terrain. From this work, we observe that each phase is characterized by a unique set of parameters requiring a careful calibration and that low-relief topographies require special consideration. Our findings could be useful for real-time hazard evaluation in future volcanic scenarios in the Michoacán–Guanajuato volcanic field and elsewhere, where new monogenetic eruptions similar to Paricutin can be expected., This research was supported by the Government of Spain through “Juan de la Cierva” postdoctoral fellowship awarded to L. Becerril; NSF EAR 1019798 (2014–2016) and a UNAM-DGAPA postdoctoral fellowship (2018–2019) granted to P. Larrea; National Science Foundation (NSF) EAR grant #1019798 awarded to E. Widom. Consejo Nacional de Ciencia y Tecnología (CONACyT-167231) and Dirección General de Asuntos del Personal Académico (UNAM-DGAPA-IN-104221) granted to C. Siebe; and VeTOOLS and EVE projects funded by the European Commission (EC ECHO SI2.695524 and 826292EC ECHO SI2.695524) granted to J. Martí.

Popocatépetl, one of the most hazardous volcanoes worldwide, poses significant threats for nearby populations in central Mexico. Therefore, it is important to reconstruct its eruptive history, including estimates of lava-flow emplacement times and their rheological properties. These studies define possible future eruptive scenarios and are necessary to mitigate the risk. Stratigraphic studies of the cal 350–50 B.C. Lorenzo Plinian pumice sequence indicate that effusive activity (Nealtican lava-flow field) occurred shortly after explosive activity, reflecting drastic changes in the eruptive dynamics. It was likely due to the efficient degassing of the magma during the Plinian phase and a decrease of magma ascent and decompression rates. Magma mixing, fractional crystallization, and a minor crust assimilation are the processes controlling the differentiation of the Nealtican lavas. We used lava chemical and mineralogical composition to estimate lava-flow viscosities, and used high-resolution elevation data to estimate emplacement times. Results indicate that lava viscosities of andesites and dacites ranged from 109 to 1012 Pa·s and emplacement durations were between ~1 and ~29 years, depending on the flow unit and morphological method employed. Considering the entire volume of emitted lava (4.2 km3) and a mean output rate of ~1 m3/s to ~15 m3/s, we estimated that the effusive phase that produced the Nealtican lava-flow field may have lasted ~35 years. This eruption had a considerable impact on pre-Hispanic settlements around the volcano, whose population exodus and relocation probably contributed to the rise of important cities in central Mexico, such as Teotihuacán and Cholula.

The origin of the large diversity of rock types erupted along the subduction-related Trans-Mexican Volcanic Belt (TMVB) remains highly debated. In particular, several hypotheses have been proposed to explain the contemporary eruption of calc-alkaline and alkaline magmas along the belt. The Michoacán-Guanajuato Volcanic Field (MGVF) is an atypical, vast region of monogenetic activity located in the western-central part of the TMVB. Here we present new petrographic, geochemical, and isotopic (Sr–Nd–Pb–Os) data on recent volcanics in the Jorullo-Tacámbaro area that is the closest to the oceanic trench. TMVB-related volcanics in this area are Plio-Quaternary (

The Serdán-Oriental lacustrine basin in the eastern part of the Trans-Mexican Volcanic Belt holds a volcanic field of >30 monogenetic vents. Among them, the ~1000-m-high, ~11 km3 Las Derrumbadas rhyolite twin domes dominate the interior of the basin and are surrounded by smaller scoria cones, lava flows, shields, tuff rings, and maars. Of interest in this area are rare endemic species encountered in some of the maar lakes, as well as the large number of pre-Hispanic archeological sites indicating that the lacustrine environment became attractive as a dwelling hub during the late Holocene. We conducted a stratigraphic and radiocarbon dating study to reconstruct the volcanic history, assess the impact of past eruptions on the environment and pre-Hispanic populations, and evaluate future volcanic hazards. Accordingly, at least 10 volcanoes were identified to be < 25,000 BC of which eight are Holocene in age (Alchichica, Tecuitlapa, Atexcac, Cerro El Brujo, Tepexitl, Aljojuca, Derrumbadas, Piedras Negras). Hence, the central part of the Serdán-Oriental basin should be considered potentially active and new eruptions are likely to occur in the future. Furthermore, we show that the ~AD 20 Las Derrumbadas eruption is one of the most voluminous silicic effusive eruptions during the Holocene worldwide. This eruption possibly triggered a migration of human populations from dispersed rural hamlets in the central part of the basin toward fewer larger urban sites (e.g. Cantona) at its margins. Finally, the young ages of the maars imply that the unique biodiversity of their crater lakes must have developed over remarkably short timescales.

Ceboruco volcano in the western Trans-Mexican Volcanic Belt is one of the eleven most active stratovolcanoes in Mexico. Due to its recent eruptive history including a large Plinian eruption ~ 1000 years ago, the AD 1870 eruption, and recurrent recent seismic activity, it seemed highly appropriate to construct a hazard map in order to be prepared for future eruptions and their associated hazards. Ceboruco volcano eruptions are predominantly effusive; however, it also has been characterized by a great variability of eruptive styles throughout its record of activity. In fact, some eruptions comprise a significant diversity of volcanic processes, including lava flows, tephra fallout, ballistic emission, pyroclastic flows and surges, and lahars. In this work, we present (1) an integrated and simplified hazard map and (2) more detailed scenario-based hazard maps showing the areas affected by the different expected volcanic phenomena attempting to account for this great diversity of eruptive processes. The maps represent the basis to identify the main hazard zones during a future eruption and the related impacts on population and infrastructure within the area of influence of Ceboruco (~ 700 km2), as well as for undertaking subsequent vulnerability and risk analyses. The maps provide a tool to develop measures of prevention and mitigation of volcanic hazards (preparedness of the population, establishment of evacuation routes and refuges, etc.), as well as for decision-making by authorities during territorial planning (urban expansion for example). The integrated simplified hazard map can also be a tool for dissemination purposes, in order to create awareness of associated hazards derived from a possible future activity of the volcano among the public in general. This is important because in the western sector of the Trans-Mexican Volcanic Belt (and specifically in the State of Nayarit) most volcanic edifices (with the exception of Colima volcano) are closed-vent volcanoes (sealed volcanic vent vs. open-vent systems) with long repose periods (up to ~ 16,000 years for example in the case of San Juan volcano 60 km to the W), a situation that consequently and unfortunately has led to a practically nonexistent volcanic risk perception.

Paricutin volcano is the youngest and most studied monogenetic cinder cone in the Michoacan-Guanajuato volcanic field (Mexico), with an excellent historical record of its nine years (February 1943 to March 1952) of eruptive activity. The eruption produced lavas and tephras that range in composition from basalt to andesite. We have conducted new major and trace element and isotopic studies (whole rock Sr-Nd-Pb-Os) of the Paricutin lavas and tephras spanning the entire duration of the eruption, together with xenoliths found in early erupted lavas and bombs, and crustal samples representative of the Paricutin basement. This work contributes to our understanding of the potential roles of mantle source heterogeneity, subduction-related metasomatism, and crustal assimilation in the petrogenesis of arc magmas; moreover this study underscores the complexity of magma generation and evolution in monogenetic volcanoes. Although Paricutin has been traditionally considered as the classical example of magma evolution by fractional crystallization and crustal contamination, our multi-isotopic study has revealed that Paricutin compositional variations are inconsistent with significant crustal assimilation. Alternatively, we suggest that Paricutin's geochemical evolution can be explained by a combination of variable degrees of fractional crystallization of magmas produced by melting heterogeneous mantle beneath the TMVB that has been metasomatized by subduction components including sediment- and oceanic crust-derived fluids.

International audience; Few monogenetic eruptions that produced lava flows have occurred in historical times, limiting the observations of their impact on human settlements. However, rheological models based on morphological and petrological datasets can contribute to decipher the eruptive dynamics and durations of ancient eruptions. The Malpaís de Zacapu, a temporal-spatial monogenetic volcano cluster at the western margin of the Zacapu lacustrine basin (Michoacán, Mexico), offers a good opportunity to apply such models because of the availability of a high-resolution LiDAR topography from which detailed morphological data was extracted. The Malpaís de Zacapu comprises late Holocene lava flow fields emplaced in the last 3200 years by four different low magnitude volcanic eruptions: Infiernillo, Malpaís Las Víboras, Capaxtiro, and Malpaís Prieto. Jointly these eruptions produced thick andesitic block lava flows covering an area of 38.3 km2 with a volume of ~ 4.4 km3. The lava viscosities at eruption vents were estimated from petro-textural analyses and range between 103 and 106 Pa s, while the final flow apparent viscosities, obtained from dimensional analyses, vary from 108 to 1010 Pa s. We estimated the mean effusion rate and lava flow emplacement duration for each flow field. Results revealed that the more viscous flows, Malpaís Las Víboras and Malpaís Prieto, could have been emplaced in less than 3 years, while the more fluid Infiernillo probably took less than 1 year. In stark contrast, the morphologically different and more voluminous Capaxtiro flow field could have been emplaced in ~ 27 years. These findings can help to evaluate the impact that these eruptions had on adjacent pre-Hispanic populations, known to have inhabited the region since at least 3000 years ago.

We conduct a probabilistic volcanic hazard assessment for Ceboruco volcano (Mexico) using PyBetVH, an e-tool based on the Bayesian event tree (BET) methodology. We use available information about the volcano, including eruptive history, numerical and theoretical models, to generate probability maps. Our hazard assessment accounts for the variability of eruption types expected at Ceboruco and the hazardous volcanic phenomena these eruptions generate. We create a generic event tree for Ceboruco to account for magmatic and amagmatic activity. For a magmatic eruption, we choose three scenarios: i) small (effusive), ii) medium (vulcanian/subPlinian) and iii) large (Plinian) based on the Holocene history of the volcano; with their related hazardous phenomena: ballistics, tephra fallout, pyroclastic density currents, lahars and lava flows. Despite numerous eruptions in the latest Holocene and efforts by several university and government groups to create and sustain a monitoring network, Ceboruco remains under-monitored, meaning that it is intermittently rather than continuously monitored by dedicated groups. With no consistent monitoring data available, we look at the geology and the eruptive history to inform our prior models. We estimate the probability of a magmatic eruption within the next time window (1 year) of ~ 0.002. We show how the BET creates higher probabilities in the absence of monitoring data. That is, there is a cost in terms of higher probabilities and higher uncertainties for having not yet developed a sustained volcano monitoring network. We present absolute probability maps (unconditional in terms of eruption size and vent location) for a magmatic eruption at Ceboruco volcano. With PyBetVH we estimate and visualize the uncertainties associated with each hazard map. Our intent is that hazard maps and uncertainties will be useful to local authorities who need to understand the hazard maps when considering the development of long-term urban and land-use planning and short-term crisis management strategies, and to the scientific community in their efforts to sustain monitoring of this active volcano.

Paricutin volcano is the youngest monogenetic cone of the Michoacán–Guanajuato volcanic field (Mexico), with an excellent historical eruption record from February 1943 to March 1952. The magma emitted during the 9 years of activity was compositionally zoned from basaltic andesite to andesite. This eruption has been considered a classic example of magma differentiation controlled by crustal assimilation combined with fractional crystallization. However, a recent geochemical study of the eruption products points to mantle source heterogeneity and fractional crystallization as the key processes involved in the compositional variability of the magmas. Here we present a detailed petrological characterization of the minerals [olivine, plagioclase, pyroxene, Cr-spinel, and (Ti-)magnetite] to shed light on the processes that led to the chemical evolution of the eruptive products. Our sample set includes the early tephra from the first weeks or months of eruption and the whole sequence of lava flows that followed. The mineral assemblage, their texture, and chemical composition show a systematic evolution between the products from the opening of the explosive vent to the effusive stage. The early tephra are basaltic andesites with oscillatory-zoned olivine and plagioclase, zoned Cr-spinel, and rare pyroxene xenocrysts. In contrast, later erupted tephra and post-January 1944 lavas are basaltic andesites and andesites with normally zoned olivine, Cr-spinel inclusions in equilibrium with the host olivine, and frequent orthopyroxene (after December 1947) with minor chemical zoning. Mineral chemistry data and olivine diffusion timescales, together with whole-rock geochemistry, suggest a convective magma regime with large temperature and oxygen fugacity gradients characterized by short timescales (few days) during the opening stage, followed by a steadier magma regime with longer timescales (few months) and including periodic magma recharge, mixing, and fractional crystallization. In addition, the mineralogical evidence we have gathered does not support considerable crustal assimilation at Paricutin. This study shows that monogenetic eruptions are far from being geochemically simple, and instead involve multiple magma batches with complex storage and mixing stages before eruption. National Research Foundation (NRF) Accepted version Dr. Helena Albert and Prof. Fidel Costa were supported by a National Research Foundation Investigatorship Award (grant number NRF-NRFI2017-06)

Ceboruco (2280 m.a.s.l.), in the western Trans-Mexican Volcanic Belt, is considered among the most hazardous volcanoes in Mexico. Some 55,000 people and important infrastructure (e.g. hydroelectric...

International audience; Given the high eruption recurrence in the Michoacán-Guanajuato volcanic field (MGVF) in central Mexico, the birth of a new monogenetic volcano can be expected in the future. It is important, therefore, to reconstruct the past eruptions of its many different volcanoes, including estimates of lava flow emplacement times and their rheological properties. These studies define the range of possible future eruptive scenarios and are necessary to evaluate potential risk. The Rancho Seco monogenetic volcano, located in the central part of the MGVF (19°37′03”N, 101°28′21”W), was radiocarbon-dated at ~27,845 years BP. Its eruption initiated with a violent-Strombolian phase that produced a scoria cone and was followed by the effusion of at least seven associated andesitic lava flows, reflecting drastic changes in the eruptive dynamics. Effusive activity probably involved decreases in the magma ascent and discharge rates linked to efficient degassing in an open system. Lava chemical composition suggest an origin of partial melting of a subduction-modified hydrated heterogenous mantle wedge and textural and mineralogical analysis indicates significant crystal fractionation and minor assimilation of granodioritic basement rocks. High-resolution LiDAR imagery was used to estimate lava flow viscosities and emplacement times by following a morphology-based methodology. Results indicate that lava flow viscosities ranged from 105 to 109 Pa·s and emplacement durations between 32 and 465 days for the flow units considered (F5 and F6). The entire eruption may have lasted from 2 to 6 years with a mean effusion rate of 4 to 15 m3/s. Our results are also pertinent to archaeologists studying the architectural remains of Angamuco, a large urban pre-Hispanic site built on Rancho Seco's lava flows.

The processes and ranges of intensive variables that control magma transport and dyke propagation through the crust are poorly understood. Here we show that textural and compositional data of olivine crystals (Mg/Fe, Ni and P) from the tephra of the first months of Paricutin volcano monogenetic eruption (Mexico, 1943–1952) record fast growth and large temperature and oxygen fugacity gradients. We interpret that these gradients are due to convective magma transport in a propagating dyke to the Earth’s surface in less than a few days. The shortest time we have obtained is 0.1 day, and more than 50% of the calculated timescales are

The Sierra Nevada Volcanic Range (SNVR), which includes Popocatépetl, Iztaccíhuatl and Tláloc-Telapón volcanoes, has been the source of multiple large explosive eruptions that have dispersed tephra across central México. Several eruptions since 40 ka have previously been described, particularly from Popocatépetl, the southernmost volcano of the range. However, the longer-term eruption history of the SNVR is poorly understood, due to challenges with correlating limited exposures of older pyroclastic sequences, and in discriminating between tephras derived from different sources. Here we describe two extensive exposures located between Popocatépetl and Iztaccíhuatl volcanoes, which provide a more complete and longer-term explosive eruption record of the SNVR: the Nepopualco and Xalitzintla tephra sequences. A detailed tephrostratigraphic survey, together with new40Ar/39Ar geochronological analyses and glass geochemistry, has permitted the characterization of identified eruption units further leading to the determination of geochemical fields for each volcano and the subsequent discernment of volcanic sources. Our results show that, since the collapse of Los Pies Cone, which destroyed the Paleo-Iztaccíhuatl edifice at 631 ± 44 ka (2σ), Iztaccíhuatl has produced at least 6 explosive rhyolitic eruptions. After coeval activity with Popocatépetl, between ~600 and ~ 500 ka, Iztaccíhuatl's explosive activity ceased while Popocatépetl's continued until present day. Popocatépetl has produced at least 27 medium to large explosive eruptions (inferred VEI 4–6), commonly of andesitic to dacitic compositions. Some of these eruptions deposited pumice fallout of >1 m thick in both the Nepopualco and Xalitzintla sequences (e.g. the 339 ± 16 ka [2σ] NT-23/WRT-7 eruption), suggesting that Popocatépetl has produced several eruptions similar in magnitude to well-known the ~14 ka Tutti Frutti Pumice (a VEI 6 eruption with a ~ 5 km3tephra volume). The Popocatépetl and Iztaccíhuatl tephras are interbedded with deposits from more distal volcanoes, including some mafic to intermediate products of unknown sources (possibly from nearby monogenetic cones) and tephras related to the late Pleistocene eruptions of Tláloc-Telapón (including the tephra layer produced by the San Valentin Ignimbrite, recently40Ar/39Ar dated in this study at ~102 ka; 2σ). Our new chemical, stratigraphic and geochronologic investigations of these pyroclastic deposits, predominantly from Popocatépetl and Iztaccíhuatl, provide information on the scale and frequency of medium to large magnitude explosive eruptions over a longer-time period than currently known and that have had potential to disperse tephra across central México since the middle to late Pleistocene. This new data can be used to determine the source of further unknown tephras in the region as well as to better assess the volcanic hazard to the densely populated megalopolis of México City.

Of the 48 volcanoes in Mexico listed as potentially active by the National Center for Disaster Prevention (CENAPRED), Ceboruco, located in the western Trans-Mexican Volcanic Belt, is considered among the 5 most hazardous. Its recent eruptive history includes a large magnitude Plinian (VEI 6) eruption ~ 1000 years ago and the historical 1870–1875 vulcanian (VEI 3) eruption, as well as recent fumarolic and seismic activity.Ceboruco is a relatively young (Three main eruptive scenarios of different magnitudes (large, intermediate, small) and eruption characteristics (likelihood of occurrence: high, medium, small) have been identified and will be presented as a background to build the volcanic hazard map for Ceboruco volcano (presented in part II of this work). Here, we report on the detailed eruptive history, with emphasis on the volcanic products of each of the eruptions, in order to identify those deposits that can serve as a reference for calibrating the modeling software (Tephra2 and Hazmap for ash fallout, Eject! code for ballistics, Etna Lava Flow Model for lava flows, Titan2D for pyroclastic density currents, and Flo-2D and LaharZ for lahars) that will be used in further steps to simulate different volcanic phenomena and lead to the construction of the hazard map.

Paricutin volcano is the youngest and most studied monogenetic volcano in the Michoacan-Guanajuato volcanic field (Mexico), with an excellent historical record of its nine years (February 1943 to March 1952) of eruptive activity. This eruption offered a unique opportunity to observe the birth of a new volcano and document its entire eruption. Geologists surveyed all of the eruptive phases in progress, providing maps depicting the volcano's sequential growth. We have combined all of those previous results and present a new methodological approach, which utilizes state of the art GIS mapping tools to outline and identify the 23 different eruptive phases as originally defined by Luhr and Simkin (1993). Using these detailed lava flow distribution maps, the volume of each of the flows was estimated with the aid of pre- and post-eruption digital elevation models. Our procedure yielded a total lava flow volume ranging between 1.59 and 1.68 km3 DRE, which is larger than previous estimates based on simpler methods. In addition, compositional data allowed us to estimate magma effusion rates and to determine variations in the relative proportions of the different magma compositions issued during the eruption. These results represent the first comprehensive documentation of the combined chemical, temporal, and volumetric evolution of the Paricutin lava field and provide key constraints for petrological interpretations of the nature of the magmatic plumbing system that fed the eruption.

The paleomagnetic dating procedure was applied to a cluster of four partly overlapping monogenetic Holocene volcanoes and associated lava flows, namely La Tinaja, La Palma, Mesa La Muerta, and Malpais de Cutzarondiro, located in the Tacambaro-Puruaran area, at the southeastern margin of the Michoacan-Guanajuato volcanic field. For this purpose, 21 sites distributed as far apart as possible from each other were sampled to obtain a well-averaged mean paleomagnetic direction for each single lava flow. For intensity determinations, double-heating Thellier experiments using the IZZI protocol were conducted on 55 selected samples. La Tinaja is the oldest of these flows and was dated by the 14 C method at ~ 5115 ± 130 years BP (cal 4184–3655 BCE). It is stratigraphically underneath the other three flows with Malpais de Cutzarondiro lava flow being the youngest. The paleomagnetic dating procedure was applied using the Matlab archaeo-dating tool in couple with the geomagnetic field model SHA.DIF.14k. Accordingly, for La Tinaja several possible age ranges were obtained, of which the range 3650–3480 BCE is closest to the 14 C age. Paleomagnetic dating on La Palma produced a unique age range of 3220–2880 BCE. Two ages ranges of 2240–2070 BCE and 760–630 BCE were obtained for Mesa La Muerta and a well-constrained age of 420–320 BCE for Malpais de Cutzarondiro. Although systematic archaeological excavations have so far not been carried out in this area, it is possible that the younger eruptions were contemporary to local human occupation. Our paleomagnetic dates indicate that all four eruptions, although closely clustered in space, occurred separately in time with varying recurrence intervals ranging between ~ 300 and ~ 2300 years. This finding should be considered when constraining the nature of the magmatic plumbing system and developing a strategy aimed at reducing risk in the volcanically active Michoacan-Guanajuato volcanic field, where several young monogenetic volcano clusters have been identified recently. These enigmatic small “flare-ups” (outbursts of small pods of magma in geologically short periods of time within a small area) have also been encountered in other subduction-related volcanic fields around the globe (e.g. Cascades arc in the western U.S.A.) and still require to be investigated by geophysical and petrological means in order to understand their origin.

International audience; "Four monogenetic Holocene lava flows located within the Michoacán-Guanajuato Volcanic Field, Mexico, were sampled for paleomagnetic dating. These flows (namely, El Infiernillo, Malpaís Las Víboras, El Capaxtiro, and Malpaís Prieto) are within the heartland of the pre-Hispanic Tarascan civilization and were inhabited repeatedly since at least 100 BC, but no relation with the volcanic evolution has been proposed so far. The stratigraphically oldest lava flow, El Infiernillo, has a radiocarbon age of 3200 ± 30 yr BP (cal. 1525–1420 BC), and it was used to validate the method. Using full-vector paleomagnetic data from three sites as input for paleomagnetic dating applying the global paleosecular variation model SHA.DIF.14k, an age range of 1500–1370 BC was obtained. Two age ranges of 1340–1230 and 1030–940 BC were obtained for Malpaís Las Víboras. A younger age range of 200–80 BC was obtained for the Capaxtiro lava flow and, finally, the Malpaís Prieto lava flow erupted within the range of AD 830–960. The human occupation history of these flows started around 100 BC during the late Pre-Classic, probably shortly after the Capaxtiro eruption. Archeological records indicate an abandonment of the entire area around AD 900 (late to terminal Classic), which coincides with the paleomagnetic age of the Malpaís Prieto eruption. Interestingly, this area was heavily repopulated again only few hundred years later around AD 1250 and belongs to the core region in which the Tarascan civilization has its roots. The eruption recurrence interval of roughly 1000 years indicates that a new monogenetic eruption should be expected to occur again in the future and that this area deserves to be studied in greater detail with particular emphasis on the impact of past eruptions. This could help to better evaluate volcanic hazards and design preparedness strategies to minimize the impact of a future eruption." (source éditeur)

The White Pumice (WP) is one of the thickest and most voluminous Plinian fallouts produced by Popocatepetl volcano in central Mexico during the Late Pleistocene-Holocene. Its eruption ~ 23,500 14 C y BP (27,800 cal BP) was triggered by the catastrophic failure of the SW flank of the volcano. The resulting debris avalanche was highly mobile reaching 72 km from the cone with an apparent coefficient of friction (L/H) of 0.06. The deposit covers an area of ~ 1200 km 2 , and has a volume of 10.4 km 3 . This gigantic landslide, characterized by exceptionally large proximal hummocks (> 400 m) provoked the sudden decompression of the hydrothermal and magmatic systems, which produced an initial blast followed by the rise of a Plinian column that reached an altitude of ~ 33 km. The isopach map allows the recognition of a dispersal axis pointing toward the south, where an area of ~ 2490 km 2 was covered by > 10 cm of pumice and ash. The total volume of the pumice fallout was estimated at ~ 1.9 km 3 DRE (Dense Rock Equivalent). Pumice clasts are dacitic (62–66 wt.% SiO 2 , anhydrous basis), highly vesicular (55–88 vol.%) and display a seriate texture with phenocrysts of plagioclase + hornblende + augite + hypersthene + oxides (Ti-magnetite and ilmenite) + apatite. As the eruption advanced, discharge rates became more intermittent and the height of the column fluctuated and finally collapsed, generating pumice-and-ash flows that were emplaced around the volcano. This short but intense activity was followed during subsequent years by rain-induced lahars that reached great distances from the volcano. At the same time, more degassed andesitic-dacitic (61–65 wt.% SiO 2 ) magma was erupted effusively (4.4 km 3 , DRE) in the new horseshoe-shaped ~ 5 km-wide crater from which the Tochimilco lava flow descended toward the SSE, where it inundated an area of ~ 68 km 2 and reached as far as ~ 22 km from its source. Since then, multiple eruptions have reconstructed the summit cone, almost completely obliterating the horseshoe-shaped crater. During the course of this catastrophic eruption (VEI = 5) a total volume of ~ 6.3 km 3 (DRE) of juvenile magma (pumice and lava) were emitted and at least an additional ~ 10 km 3 of pre-existing rocks (debris avalanche) mobilized. It surpasses in magnitude most other known Plinian eruptions from Popocatepetl and can be envisaged as an example of a worst-case scenario for hazard evaluation purposes. It dramatically changed the morphology of the volcano and had profound and far-reaching effects beyond its immediate vicinity along rivers draining surrounding plains as well as on the lacustrine basins (e.g. Chalco) to the NE. A repeat of such an eruption in this densely populated area would certainly cause a major calamity of unprecedented dimensions.

The recent identification of Holocene volcanic clusters in small areas within the Michoacan Guanajuato Volcanic Field (MGVF) opens several questions regarding future volcanic hazard assessments in this region. Documenting vent alignments and eruption recurrence intervals within clusters will provide parameters necessary for making temporal and spatial hazard evaluations. Here, we present a possible new case of a small cluster consisting of only two monogenetic volcanoes, El Astillero and El Pedregal located in the ~ 4400-km2 Tancitaro-Nueva Italia region in the southwestern part of the MGVF, only 25 km to the south of Paricutin volcano. We determined from paleomagnetic and radiocarbon dating that El Astillero and El Pedregal most likely erupted one after the other between AD 500 and 700 (within the Late Classic period of Mesoamerican archeology). While the eruptions were likely separated by a short period of time, the exact length is difficult to ascertain. After the ~ 6 years of total estimated eruption duration of the two volcanoes, both together occupied an area of 14.7 km2 and emitted a dense rock equivalent (DRE) volume of magma of ~ 0.5 km3. Notable characteristics of the eruptions include a switch from the explosive activity exclusive of El Astillero (Strombolian) to effusive activity early after the initiation of the El Astillero eruption, a shift in the active vents, and a progressive change in the bulk magma composition from basaltic andesite to andesite throughout the duration of the eruption. This activity first formed the El Astillero scoria cone and tephra deposits followed by its lava field and ended with the emplacement of the El Pedregal viscous lavas. The discovery of pre-Hispanic pottery sherds and obsidian artifacts underneath the El Astillero tephra fallout unambiguously attests to human activities in the area before the eruption. Judging by their eruptive style, the eruptions probably had a limited impact on the small area affected and the surrounding human activities, but the hazard for this area remains since El Astillero and El Pedregal could represent the initial stages of a new cluster that is still in the making. If so, another eruption should be expected in this area again.

We present 32 new paleomagnetic directions and 21 absolute paleomagnetic intensities (PI) from 33 volcanoes, sampled at 66 sites and covering the last 46 ka. Of these, 29 were radiocarbon-dated, 3 by thermo-luminescence, and one is of historical age (AD 1793). Rock magnetic experiments show that the dominant minerals are magnetite and titanomagnetite of low to intermediate titanium content, and of pseudo single domain size. Paleodirections were determined using stepwise demagnetization protocols, and PI by the IZZI or Thellier-Coe protocols, and strict selection criteria were applied to ensure the reliability of the data. Previously published data were evaluated to fulfill similar quality criteria as our data, resulting in: 65 directional data point; 18 paleointensity entries from lavas; 59 archeointensities are found to be acceptable. All accepted data come from a region within an 860 km radius around Mexico City. Paleosecular variation (PSV) curves of the past geomagnetic full-vector were established by using the bootstrap-resampling algorithm combined with cubic P-Splines for smoothing and interpolation. Because of the uneven time distribution of the data, this was done for two successive periods, between AD 2000 – 1600 BC and 1600 BC - 44000 BC. The full-vector PSV curves are unique for the American continents because of their temporal extension end because they include both, directions and absolute PI. The recent PSV curves, the last 3600 years, are of high resolutions which certainly have implication for both regional and global geomagnetic field models. Fast PSV change centered around AD 700 and AD 900, separated by a period of much slower PSV were observed, and rapid PI changes were found around 400 BC and AD 1000. In the period between 1600 BC and 44000 BC, PSV curves are well defined only within some periods and otherwise only define general PSV trends. Several intensity peaks with values up to 65 μT (VADM 15⋅1022 Am2) were observed around 250 BC, 12000 BC, 15000 BC and 27000 BC, and intensity lows around AD 700, 1200 BC, 24000-17000 BC, and 34000 BC. Abnormal directions were found around 26000 BC, with negative inclinations down to about -30°, which may be related to the Mono Lake or Rockall event. A comparison with other PSV curves is complicated by the large distance to Europe and the Hawaiian islands, with longitude differences of 99° and 57°, respectively. Lake sediment data from southern Texas show more differences than agreements, suggesting that either of the data may be affected by systematic errors.

Potrerillo I, Potrerillo II, and San Juanito volcanoes are part of the 28 Late Quaternary monogenetic eruptive vents concentrated along a ~2-km-wide and ~30-km-long stripe in the vicinity of Ceboruco stratovolcano (western Mexican Volcanic Belt). The studied volcanoes are closely spaced and located within a ~12 km2 sub-drainage basin, northwest of Ceboruco's edifice. Eruptive dynamics were inferred from sedimentary, stratigraphic, and pyroclast characteristics. Unlike Potrerillo I, which was formed by an entirely dry explosive magmatic eruption, evidence for the prevalence of initial short-lived phreatomagmatic phases was found for the Potrerillo II and the San Juanito eruptions that ended effusively. In this study we examine the nature and proportion of different types of pyroclasts within the exposed deposits of these three volcanoes, as well as their sedimentary features to better understand the initiation and progression of their eruptions. Our results indicate that both Potrerillo II and San Juanito tephra ring deposits show dominantly atypical, crudely bedded, coarse-grained deposits where the evidence for energetic, diluted pyroclastic density currents is scarce or subordinated. Instead, low energy, shallow seated, phreatomagmatic explosions generated medium-to-coarse grain-sized pyroclasts that were transported within dense tephra jets that were ballistically ejected, which on deposition formed non-turbulent currents with non-extensive lateral movement. The nature of such eruptive style was controlled by the substrate hydrogeology conditions that prevailed at the time of the eruption. So, magmas of different composition (dacitic for Potrerillo II, and basaltic andesite for San Juanito) followed similar dynamics when interacting with water. We propose that fractured aquifers with shallow water tables (or even surface water) existed at the time of both eruptions and interacted explosively with the magmas. In contrast, the construction of Potrerillo I scoria cone, which is related exclusively to explosive magmatic activity, does not show evidence of phreatomagmatic activity. This eruption may have occurred when the water table was deep, or surface water was unavailable. The variations in the depth of phreatomagmatic explosions, the availability of the water involved in the phreatomagmatic phases, and the absence or presence of these phases in the studied volcanoes were probably strongly influenced by the water-bearing conditions of the aquifers at the time of the eruption, which in turn, depended on the amount and distribution of annual rainfall. This study improves our understanding of phreatomagmatic eruptions of diverse magmatic compositions in similar settings. The recognition of associated hazards will allow to further define eruptive scenarios of monogenetic eruptions and help update the volcanic hazard map of the Ceboruco volcano area in the future.

The 1759–1774 eruption of the Jorullo volcano in the Michoacan Guanajuato Volcanic Field (MGVF), Mexico, produced lavas that range in composition from basalt to basaltic andesite. We have conducted new major and trace element and isotopic studies (whole rock Sr–Nd–Pb–Hf–Os, and O isotopes in olivine separates) of the Jorullo lavas and tephras spanning the duration and compositional range of the eruption, to further constrain the potential roles of mantle source heterogeneity, subduction-related metasomatism, and crustal assimilation in the petrogenesis of the Jorullo magmas. This study presents the first Hf, high precision Pb and comprehensive oxygen isotope measurements for Jorullo volcanic rocks. All samples have arc-like trace element patterns with enrichments in large ion lithophile elements (e.g. Ba, Rb, and Pb) and depletions in fluid immobile elements (e.g. Nb, Ta). In addition, the samples show variations in 87Sr/86Sr (0.7038–0.7040), 143Nd/144Nd (0.51280–0.51285), 176Hf/177Hf (0.28297–0.28300), 206Pb/204Pb (18.62–18.66), 207Pb/204Pb (15.57–15.59) and 208Pb/204Pb (38.34–38.43). Osmium isotope signatures are, with one exception, more radiogenic than the depleted and primitive mantle (187Os/188Os = 0.1231–0.1616). Oxygen isotope ratios of olivine phenocrysts (δ18.OSMOW = 5.70–6.02‰) show limited variation, but are isotopically heavier than normal mantle olivine. The samples define two geochemical groups: high-MgO samples with higher 87Sr/86Sr, lower 143Nd/144Nd and 176Hf/177Hf, and a positive correlation of Sr and Pb isotopes; and low-MgO samples displaying lower 87Sr/86Sr but higher 143Nd/144Nd and 176Hf/177Hf than the former group, and a negative correlation of Sr and Pb isotopes. The high-MgO group comprises most of the early tephra and lavas, whereas the low-MgO group includes most of the late tephra and lavas. These compositional variations are inconsistent with shallow level contamination, but rather are interpreted to reflect mantle source heterogeneity. Trace element and isotopic signatures are consistent with North Mexican Extensional Province (NMEP) mantle metasomatised by subduction components composed of sediment- and oceanic crust-derived hydrous fluid. The temporal–compositional variations observed in Jorullo magmas are inferred to result from a combination of variable degrees of fractional crystallization of magmas produced by tapping a progressively less metasomatised mantle source that is vertically and/or laterally heterogeneous.

Geologic mapping of two neighbouring areas (totalling ~770 km2) centred around the Rancho Seco and Mazcuta monogenetic scoria cones and situated between the Patzcuaro and Zacapu lake basins in the Michoacan-Guanajuato Volcanic Field (central portion of the Trans-Mexican Volcanic Belt), allowed the recognition of 62 Quaternary monogenetic volcanic structures, which include cinder cones with associated lava flows, domes, and small-to-medium sized shields. 40Ar/39Ar and 14C radiometric dating, petrography, and whole-rock chemical analyses of volcanic products provide a stratigraphic framework and insight into different eruptive styles, and erupted volumes (~45 km3 of calc-alkaline magma). Pliocene to Holocene monogenetic activity has been frequent in this region, forming structures, which are generally aligned along an ENE-WSW direction associated to the Morelia-Cuitzeo-Acambay normal fault system. The young Rancho Seco and Mazcuta volcanoes are of particular interest because their distal lava flows host the pre-Hispanic archaeological urban centres of Angamuco and Cortijo Viejo, respectively. The Rancho Seco scoria cone was radiocarbon-dated at 27,845 + 445/−425 yr BP and emitted at least six andesitic lava flows which were emplaced toward the SW (Lake Patzcuaro) covering an area of 21.3 km2 with a volume of ~0.64 km3. The Mazcuta scoria cone dated at 7970 ± 135 yr BP produced five basaltic andesite-andesite lava flows toward the NW (Lake Zacapu), where they cover an area of 28.85 km2 with a volume of ~0.57 km3. The recently studied archaeological site of Angamuco became an important urban centre during the rise of the Tarascan Empire in the Post-Classic period (900–1521 CE), while the Cortijo Viejo site remains largely unexplored, but its occupation might fall within the same period. Although the young lava flows on which these sites are built seem inhospitable and barren with a rugged topography and rocky substrate unfit for agriculture, early inhabitants adapted and modified its surface according to their needs. Hence, these archaeological sites exemplify how a seemingly hostile landscape was ingeniously modified to establish population centres with patterns similar to those observed on lava flows elsewhere.

International audience; The Zacapu lacustrine basin is located in the north-central part of the Michoacán-Guanajuato volcanic field (MGVF), whichconstitutes the west-central segment of the Trans-Mexican Volcanic Belt. Geological mapping of a 395 km2 quadrangleencompassing the western margin of the basin, 40Ar/39Ar and 14C radiometric dating, whole-rock chemical and petrographicanalyses of volcanic products provide information on the stratigraphy, erupted volumes, age, and composition of the volcanoes.Although volcanism in the MGVF initiated since at least 5 Ma ago, rocks in the western Zacapu lacustrine basin are all youngerthan ~ 2.1 Ma. A total of 47 volcanoes were identified and include 19 viscous lava flows (~ 40 vol.%), 17 scoria cones withassociated lava flows (~ 36 vol.%), seven lava shields (~ 15 vol.%), three domes (~ 6 vol.%), and one maar (~ 2 vol.%). Eruptedproducts are dominantly andesites with 42 km3 (~ 86 vol.%) followed by 4 km3 of dacite (~ 8 vol.%), 1.4 km3 of basaltic trachyandesite(~ 3 vol.%), 1 km3 of basaltic andesite (~ 2 vol.%), and 0.14 km3 of rhyolite (~ 0.3 vol.%). Eruptive centers arecommonly aligned ENE-WSW following the direction of the regional Cuitzeo Fault System. Over time, the high frequency oferuptions and consequent accumulation of lavas and pyroclastic materials pushed the lake’s shore stepwise toward the southeast.Eruptions appear to have clustered through time. One cluster occurred during the Late Pleistocene between ~ 27,000 and ~21,300 BC when four volcanoes erupted. A second cluster formed during the Late Holocene, between ~ 1500 BC and ~ AD 900,when four closely spaced monogenetic vents erupted forming thick viscous ‘a’a to blocky flows on the margin of the lacustrineflats. For still poorly understood reasons, these apparently inhospitable lava flows were attractive to human settlement andeventually became one of the most densely populated heartlands of the pre-Hispanic Tarascan civilization. With an averageeruption recurrence interval of ~ 900 years during the Late Holocene the western Zacapu lacustrine basin is one of the most activeareas in the MGVF and should hence be of focal interest for regional volcanic risk evaluations.

Limestone assimilation and skarn formation are important processes in magmatic systems emplaced within carbonate-rich crust and can affect the composition of the magma and that of associated volcanic gas. In this study we focus on marble and calc-silicate (skarn) xenoliths from contact reactions between magma and carbonate wall-rock of the Vesuvius volcanic system. We present new elemental and C-O isotope data for marble and skarn xenoliths as well as for igneous rocks collected from the AD 79 (Pompeii) and AD 472 (Pollena) eruptions. The igneous samples have consistently high δ 18 O values (9.3 to 10.8‰), but low H 2 O contents (≤ 1.5%), indicating that magma–crust interaction prior to eruption took place. The marble xenoliths, in turn, record initial decarbonation reactions and fluid-mass exchange in their textures and δ 13 C and δ 18 O ranges, while the skarn xenoliths reflect prolonged magma–carbonate interaction and intense contact metamorphism. Skarn-xenoliths record Ca and Mg release from the original carbonate and uptake of Al and Si and span the full δ 18 O data range from un-metamorphosed carbonate (> 18‰) to values typical for Vesuvius magmatic rocks (~ 7.5‰), which implies that skarn xenoliths comprise carbonate and magmatic components. Textural and chemical evidence suggest that direct carbonate dissolution into the host magmas occurred as well as post-metamorphic skarn recycling, resulting in progressive Ca and Mg liberation from the skarn xenoliths into the magma. Magma–carbonate interaction is an additional source of CO 2 during carbonate break-down and assimilation and we calculate the amount of extra volatile components likely liberated by contact metamorphic reactions before and during the investigated eruptions. We find that the extra CO 2 added into the volcanic system could have outweighed the magmatic CO 2 component by ≥ factor seven and thus likely increased the intensity of both the Pompeii and the Pollena eruptive events.

The Michoacán–Guanajuato Volcanic Field is the largest subduction-related monogenetic volcanic field in the world and includes more than 1000 scoria cones and a few hundred medium-sized volcanoes. Although medium-sized volcanoes (domes and shields) are less abundant, hazards associated with the renewal of this type of activity should not be neglected. Here, we focus on El Metate volcano, the morphologically youngest shield of the field. This volcano has a minimum volume of ~9.2 km3 DRE, and its viscous lava flows were emplaced during a single eruption over a period of ~30 years covering an area of 103 km2. El Metate is thus best labeled as a monogenetic andesite shield. This eruption had a significant impact on the environment (modification of the hydrological network, forest fires, etc.), and hence, nearby human populations probably had to migrate. New C14 dates for the eruption yield a young age (~AD 1250), which briefly precedes the initial rise of the Tarascan Empire (AD 1350–1521) in this region. By volume, this is certainly the largest eruption during the Holocene in the Trans-Mexican Volcanic Belt, and it is the largest andesitic effusive eruption known worldwide for this period. Such a large volume erupted in a relatively short time bears important implications for evaluating future hazards in the Michoacán–Guanajuato Volcanic Field.

The Late Pleistocene (~ 21,000 yr BP) Alberca de Guadalupe maar is one of the few phreatomagmatic volcanoes occurring within the scoria-cone dominated Plio-Quaternary Michoacan-Guanajuato Volcanic Field. The scarcity of this type of volcano implies that conditions favoring their formation are rarely met in this region. We identify these factors by implementing current methods of investigation with emphasis on hydrogeological conditions. We present the stratigraphy (including a set of 40 Ar/ 39 Ar and 14 C dates) of the SE margin of the Zacapu intermontane tectonic basin, where the maar just forms a hole (~ 1 km in diameter, ~ 150 m deep, bearing a ~ 9 m deep lake) in the otherwise planar topography of the underlying early Pleistocene lava flows of the Cerro Pelon scoria cone. The maar is composed of typical phreatomagmatic surge deposits that are poorly sorted and rich in accidental lithics (> 60 wt.% of the deposit) with few juveniles (basaltic andesite, SiO 2 = 54–58 wt.%). The entire structure is cut by an ENE–WSW trending normal fault and is underlain by andesite lavas and silicic ignimbrites (partly inferred from xenoliths encountered in the maar deposits) that are Miocene to Early Pleistocene in age. The crater is at the center of a N–S elongated drainage basin surrounded by topographic highlands that channel water with high hydraulic pressure from most directions towards the location of the maar. This geometric configuration was already in existence at the time of the maar-forming eruption, but the climate was different. Colder and more humid conditions during the Last Glacial Maximum (Cw2-climate type, annual precipitation of > 1000 mm) favored the saturation of the fractured shallow aquifer system (hydraulic conductivity of 10 − 8 to 10 − 7 m/s) that supplied sufficient groundwater at a high flow rate directed towards the center of the basin. Upon contact near surface ( 150 m deep crater with steep inner walls and an underlying shallow diatreme (

International audience; In a recent study, Chevrel et al. (2016a, b) radiocarbon-dated the oldest lava flow of the voluminous (~ 9.2 km3) El Metate shield volcano (Michoacán, Mexico) at cal 1250–1260 CE and proposed that its eruption was monogenetic in origin, with twelve younger lava flows emplaced during a short period of only ~ 35 years, but certainly < 275 years. In order to test this hypothesis, we undertook a detailed paleomagnetic study of five lava flows from El Metate to check the consistency of their paleomagnetic directions. Additionally, a group of representative specimens was treated with the double-heating Thellier experiment using the IZZI protocol for paleointensity determination. Flow mean paleomagnetic directions obtained for four of the flows are indistinguishable, and discordant directions were obtained from the site of the 5th flow measured, probably due to the tilting of the sampled block after remanence acquisition. Mean paleodirections and intensities were used for paleomagnetic dating applying the global paleosecular variation model SHA.DIF.14k. The resulting age range for the eruption is 1150–1290 CE, which overlaps with the range previously determined by the 14C method by Chevrel et al. (2016a). Accepting the 14C age of the oldest flow as the maximum age, the age range would be reduced to 1250–1290 CE, which strongly supports the hypothesis of a monogenetic nature of the El Metate eruption.

More than 350 oriented paleomagnetic cores were obtained for rock-magnetic and paleomagnetic analysis from radiometrically dated (40Ar–39Ar) magmatic rocks occurring in the southern segment (Jorullo and Tacambaro areas) of the Michoacan-Guanajuato Volcanic Field in the Trans-Mexican Volcanic Belt. Most of the lavas (37) stem from monogenetic volcanoes dated at less than 4 Ma. Two additional sites were sampled from the plutonic basement dated at 33–30 Ma. Primary remanences carried by low-Ti titanomagnetites allowed to determining 34 reliable site-mean directions of mostly normal (27) but also reversed (7) polarities. The mean directions of these two populations are antipodal, and suggest neither major vertical-axis rotations with respect to the North America craton nor tilting in the region for the last 4 Ma (rotation and flattening of the inclination parameters being less than −5.9 ± 3.8 and 0.1 ± 3.9, respectively). The corresponding paleomagnetic pole obtained for Pliocene–Pleistocene times is PLAT = 83.4°, PLON = 2.4° (N = 32, A95 = 2.7°). Virtual geomagnetic poles also contribute to the time averaged field global database and to the paleosecular variation (PSV) investigations at low latitudes from lavas for the last 5 Ma, showing a geomagnetic dispersion value that is in agreement with available PSV models. When comparing the magnetic polarities and corresponding radiometric ages of the studied sites with the Cenozoic geomagnetic polarity time scale (GPTS), a good correlation is observable. This finding underscores the suitability of data obtained on lavas in Central Mexico for contributing to the GPTS. Furthermore, the detection of short-lived geomagnetic features seems possible, since the possible evidence of Intra-Jaramillo geomagnetic excursion could be documented for the first time in these volcanic rocks.

The recent paper by Straub et al. (2012) provides a detailedgeochemical study of the compound Texcal lava flow andthe eruptive products of Chichinautzinvolcano, twomono-genetic volcanoes located in close proximity to each otherin the central part of the Sierra Chichinautzin VolcanicField (SCVF) south of Mexico City. The authors chosethese mafic [ocean island basalt (OIB)-type] volcanoesthat belong to the Mexican Volcanic Belt because theyerupted lavas displaying a range of compositions and inaddition are believed to have retained some of their initialgeochemical sub-arc mantle and subducted slab signatures.The latter allowed these authors to make inferences re-garding magma generation processes in a subduction-related tectonic setting.I would like to comment here on one specific point onwhich I hold a significantly different opinion, and whichis important to address because of its diverse ramifications(including volcanic hazard assessment in a densely popu-lated area). This concerns the exact location and morph-ology of the vent(s) and the timing and eruptive style ofthe eruption that produced the Texcal lava flows. In theirfig. 1, Straubet al. (2012) present a geological sketch map,which they call a‘refined’ version of a previous map pub-lished by Siebe et al. (2004a, 2004b). At first sight, the‘refined’map seems almost identical to the map publishedby Siebe et al. (2004a, 2004b). However, a closer look (seeFig. 1a) reveals that the source vent for the compoundTexcal lava flow has been changed.The Guespalapa align-ment of scoria cones, which formed between 4700 and2800 years

International audience; Medium-sized volcanoes, also known as Mexican shields due to their andesitic composition and slightly higher slope angles in comparison to Icelandic shields, occur across the Trans-Mexican Volcanic Belt and represent nearly one third of all volcanic edifices in the Michoacán-Guanajuato Volcanic Field (MGVF). Many questions about their origin and eruptive dynamics remain unanswered. Here, we focus on El Metate, the youngest (∼AD 1250) monogenetic shield volcano of the MGVF and the most voluminous (∼9.2 km3 dense rock equivalent) Holocene eruption in Mexico. Its eruptive history was reconstructed through detailed mapping, geochemical analysis (major and trace elements, Sr-Nd-Pb isotopic data), and rheological study of its thick andesitic flows. Early and late flow units have distinct morphologies, chemical and mineralogical compositions, and isotopic signatures which show that these lavas were fed by two separate magma batches that originated from a heterogeneous mantle source and followed distinct differentiation paths during their ascent. Thermobarometry calculations constraining the conditions of crystallization indicate a temporary storage of the last erupted magma batch at a depth of ∼7–10 km. Lava rheology was estimated using petrographic characteristics, geochemical data, and flow dimensions. The magma viscosity increased from 102–103 Pa s prior to eruption through 106–108 Pa s during ascent, to 109–1011 Pa s during lava emplacement. Though magma viscosity was quite high, the eruption was purely effusive. The explosive eruption of such a large magma volume was probably avoided due to efficient open system degassing (outgassing) of the magma as it ascended through the uppermost crust and erupted at the surface.

The 690 km2 Tacambaro-Puruaran area located at the arc-front part of the Michoacan-Guanajuato volcanic field in the Trans-Mexican Volcanic Belt (TMVB) records a protracted history of volcanism that culminated with intense monogenetic activity in the Holocene. Geologic mapping, 40Ar/39Ar and 14C radiometric dating, and whole-rock chemical analyses of volcanic products provide insights to that history. Eocene volcanics (55–40 Ma) exposed at uplifted blocks are related to a magmatic arc that preceded the TMVB. Early TMVB products are represented by poorly exposed Pliocene silicic domes (5–2 Ma). Quaternary ( 30 km) may be related to high rates of magma production at depth and a favorable tectonic setting.

Volcan Popocatepetl (Mexico) erupted ~ 14,100 14 C yr BP (~ 17,000 cal yr BP) producing the Tutti Frutti Plinian Eruption (TFPE). The eruption tapped two different silicic magmas (GT and MT) that mixed just prior and during the eruption, resulting in the collapse of the reservoir and formation of a caldera. Two fall deposits (GT and MT) and two series of pyroclastic flows (P01 and P02) were emplaced during the eruption. These were studied at 91 sites, where thicknesses were measured, and at many sites the five coarsest lithics observed in each unit were measured. Several samples from deposits were sieved for component analysis. The eruption began with intermittent, short lived eruptions that deposited the GT unit at proximal sites around the volcano. Next, the main Plinian phase of the eruption started, and the MT unit and a pyroclastic flow were deposited to the northwest of the present-day cone. Overall, ~ 3 km 3 of magma were erupted. The pyroclastic flow within MT separates two fall units characterized by different pumice color and lithic content. During deposition of the lower unit (milky pumice) eruptive intensity reached 3 × 10 8 kg s − 1 , producing a Plinian column 37 ± 2 km in height. After emplacement of the pyroclastic flow, a lithic-rich upper unit (orange pumice) was deposited with a peak intensity of 5 × 10 8 kg s − 1 , producing a Plinian column 44 ± 2 km in height. Lithics in the TFPE vary from only volcanic (~ 5 vol.%) in GT, to volcanic, granodiorite, and metamorphic (up to 50 vol.%) in MT. The shift in components and lithic content was produced by the collapse of the reservoir. We suggest that the reservoir was over-pressured because of mixing between GT and MT magmas, and then relaxed when all of GT, and part of MT magma were tapped, triggering collapse. The characteristics of mixing were elucidated by studying banded pumice and mixed populations of crystals found in pumice from both units. In addition, the occurrence of An-rich plagioclase, Mg-rich pyroxene, and Cr-rich magnetite crystals revealed intimate mixing of more mafic magma with MT.