Volcán Citlaltépetl (Pico de Orizaba) with an elevation of 5,675 m is the highest volcano in Nort... more Volcán Citlaltépetl (Pico de Orizaba) with an elevation of 5,675 m is the highest volcano in North America. Its most recent catastrophic events involved the production of pyroclastic flows that erupted approximately 4,000, 8,500, and 13,000 years ago. The distribution of mapped deposits from these eruptions gives an approximate guide to the extent of products from potential future eruptions. Because the topography of this volcano is constantly changing computer simulations were made on the present topography using three computer algorithms: energy cone, FLOW2D, and FLOW3D. The Heim Coefficient (µ), used as a code parameter for frictional sliding in all our algorithms, is the ratio of the assumed drop in elevation (H) divided by the lateral extent of the mapped deposits (L). The viscosity parameter for the FLOW2D and FLOW3D codes was adjusted so that the paths of the flows mimicked those inferred from the mapped deposits. We modeled two categories of pyroclastic flows modeled for the level I and level II events. Level I pyroclastic flows correspond to small but more frequent block-and-ash flows that remain on the main cone. Level II flows correspond to more widespread flows from catastrophic eruptions with an approximate 4,000-year repose period. We developed hazard maps from simulations based on a National Imagery and Mapping Agency (NIMA) DTED-1 DEM with a 90 m grid and a vertical accuracy of ±30 m. Because realistic visualization is an important aid to understanding the risks related to volcanic hazards we present the DEM as modeled by FLOW3D. The model shows that the pyroclastic flows extend for much greater distances to the east of the volcano summit where the topographic relief is nearly 4,300 m. This study was used to plot hazard zones for pyroclastic flows in the official hazard map that was published recently.
Journal of Volcanology and Geothermal Research, 2015
Abstract The Late Pleistocene (~ 21,000 yr BP) Alberca de Guadalupe maar is one of the few phreat... more Abstract 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 (
... 1). The three most recent of these explosive eruptions occurred within the period of human oc... more ... 1). The three most recent of these explosive eruptions occurred within the period of human occupation, between 3195 and 2830 BC, 800 and 215 BC, andA. D. 675 and 1095, with devastating Page 270. ... Major eruptions occurred ca. 3050 BC, 200 BC, and AD 823 (Fig. ...
The 690 km2 Tacámbaro-Puruarán area located at the arc-front part of the Michoácan-Guanajuato vol... more The 690 km2 Tacámbaro-Puruarán area located at the arc-front part of the Michoácan-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 (<2 Ma) volcanoes (114 mapped) are mainly scoria cones with lavas (49 vol.%), viscous lava flows (22 vol.%), and lava shields (22 vol.%). Erupted products are dominantly either basaltic andesites (37 vol. %), or andesites (17 vol.%), or span across both compositions (28 vol.%). Basalts (9 vol.%), dacites (4 vol.%), shoshonites (2 vol.%), and other alkali-rich rocks (<3 vol.%) o...
. Volcanic signatures archived in polar ice sheets provide important opportunities to date and co... more . 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.
The Serdán-Oriental lacustrine basin in the eastern part of the Trans-Mexican Volcanic Belt holds... more 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, Der...
Abstract Paricutin volcano is the youngest and most studied monogenetic volcano in the Michoacán-... more Abstract Paricutin volcano is the youngest and most studied monogenetic volcano in the Michoacán-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&#39;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 1.68km³ 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.
Journal of Volcanology and Geothermal Research, 2017
Claus Siebe, Sergio Salinas, Lilia Arana-Salinas, José Luis Macías, James Gardner, Rosanna Bonasi... more Claus Siebe, Sergio Salinas, Lilia Arana-Salinas, José Luis Macías, James Gardner, Rosanna Bonasia The White Pumice (WP) is one of the thickest and most voluminous Plinian fallouts produced by Popocatépetl volcano in central Mexico during the Late Pleistocene-Holocene. Its eruption ~ 23,500 14C 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 km2, and has a volume of 10.4 km3. This gigantic landslide, characterized by exceptionally large proximal hummocks (&gt; 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 km2 was covered by &gt; 10 cm of pumice and ash. The total volume of the pumice fallout was estimated at ~ 1.9 km3 DRE (Dense Rock Equivalent). Pumice clasts are dacitic (62–66 wt.% SiO2, 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.% SiO2) magma was erupted effusively (4.4 km3, 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 km2 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 km3 (DRE) of juvenile magma (pumice and lava) were emitted and at least an additional ~ 10 km3 of pre-existing rocks (debris avalanche) mobilized. It surpasses in magnitude most other known Plinian eruptions from Popocatépetl 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 1759-1774 eruption of the Jorullo volcano in the Michoacán Guanajuato Volcanic field (MGVF), ... more The 1759-1774 eruption of the Jorullo volcano in the Michoacán 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 87 Sr/ 86 Sr
The Jorullo monogenetic volcano erupted 250 years ago at the southern border of the Trans-Mexican... more The Jorullo monogenetic volcano erupted 250 years ago at the southern border of the Trans-Mexican Volcanic Belt (TMVB), an area that records a long history of magmatic and tectonic activity. The oldest rocks that crop out in the area are early-Oligocene (32.7 ± 0.2 Ma) dioritic to granitic (60-72 wt.% SiO 2) plutons intruded by younger to contemporaneous (30.3 ± 0.1 and 33.3 ± 0.7 Ma) aplitic (76-78 wt.% SiO 2) dikes and mineralized veins. Volcanic rocks related to these intrusives form a thick sequence exposed in cliffs, from the base of which an altered andesite (58 wt.% SiO 2) was collected. The nearby epithermal Cu-mineralization of the Inguarán mining area to the southeast is also related to this Tertiary volcanic episode. The oldest expression of the TMVB in this area is represented by Pliocene (3.2-2.4 Ma) basaltic andesite to andesite (53-63 wt.% SiO 2) lavas (with pyroxene ± olivine) forming extensive mesas, eroded mounds, and thick elongate flows, that were unconformably deposited on top of the Oligocene rocks. Their emplacement was followed by erosion approximating a rate of 100 m/Ma over the past 3 Ma. This led to the formation of an inverted topography reflecting the higher resistance to erosion of these lavas that were originally deposited in valleys and today constitute prominent mesas. During the last 1 Ma, at least twenty-six monogenetic scoria cones formed in the study area, erupting about 10.2 km 3 of lava and pyroclastics dominantly composed of olivine and pyroxenebearing andesites (61 vol.% DRE), lesser basaltic andesites (30 vol.% DRE), and a minority of olivine-rich basalts (10 vol.% DRE). These eruptive products include the K-rich basaltic trachyandesites of Cerro La Pilita, a scoria and lava cone located close to Jorullo. The ≤ 27 ka San Hilario and Esmeralda lavas, which are located 13 km southeast of Jorullo, are the southernmost eruptive products of the TMVB and also the youngest volcanoes after Jorullo in this area. Mapping of main faults and scoria cone alignments on regional and local scales reveals that the ascent of dikes feeding Quaternary eruptions in the Jorullo area was controlled by westnorthwest and west-southwest basement structures, northeast-oriented subduction-related horizontal compressional stress probably associated with crustal fractures, and a major northwest-trending seismically active fault zone that passes near Paricutin and Jorullo.
Volcán Citlaltépetl (Pico de Orizaba) with an elevation of 5,675 m is the highest volcano in Nort... more Volcán Citlaltépetl (Pico de Orizaba) with an elevation of 5,675 m is the highest volcano in North America. Its most recent catastrophic events involved the production of pyroclastic flows that erupted approximately 4,000, 8,500, and 13,000 years ago. The distribution of mapped deposits from these eruptions gives an approximate guide to the extent of products from potential future eruptions. Because the topography of this volcano is constantly changing computer simulations were made on the present topography using three computer algorithms: energy cone, FLOW2D, and FLOW3D. The Heim Coefficient (µ), used as a code parameter for frictional sliding in all our algorithms, is the ratio of the assumed drop in elevation (H) divided by the lateral extent of the mapped deposits (L). The viscosity parameter for the FLOW2D and FLOW3D codes was adjusted so that the paths of the flows mimicked those inferred from the mapped deposits. We modeled two categories of pyroclastic flows modeled for the level I and level II events. Level I pyroclastic flows correspond to small but more frequent block-and-ash flows that remain on the main cone. Level II flows correspond to more widespread flows from catastrophic eruptions with an approximate 4,000-year repose period. We developed hazard maps from simulations based on a National Imagery and Mapping Agency (NIMA) DTED-1 DEM with a 90 m grid and a vertical accuracy of ±30 m. Because realistic visualization is an important aid to understanding the risks related to volcanic hazards we present the DEM as modeled by FLOW3D. The model shows that the pyroclastic flows extend for much greater distances to the east of the volcano summit where the topographic relief is nearly 4,300 m. This study was used to plot hazard zones for pyroclastic flows in the official hazard map that was published recently.
Journal of Volcanology and Geothermal Research, 2015
Abstract The Late Pleistocene (~ 21,000 yr BP) Alberca de Guadalupe maar is one of the few phreat... more Abstract 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 (
... 1). The three most recent of these explosive eruptions occurred within the period of human oc... more ... 1). The three most recent of these explosive eruptions occurred within the period of human occupation, between 3195 and 2830 BC, 800 and 215 BC, andA. D. 675 and 1095, with devastating Page 270. ... Major eruptions occurred ca. 3050 BC, 200 BC, and AD 823 (Fig. ...
The 690 km2 Tacámbaro-Puruarán area located at the arc-front part of the Michoácan-Guanajuato vol... more The 690 km2 Tacámbaro-Puruarán area located at the arc-front part of the Michoácan-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 (<2 Ma) volcanoes (114 mapped) are mainly scoria cones with lavas (49 vol.%), viscous lava flows (22 vol.%), and lava shields (22 vol.%). Erupted products are dominantly either basaltic andesites (37 vol. %), or andesites (17 vol.%), or span across both compositions (28 vol.%). Basalts (9 vol.%), dacites (4 vol.%), shoshonites (2 vol.%), and other alkali-rich rocks (<3 vol.%) o...
. Volcanic signatures archived in polar ice sheets provide important opportunities to date and co... more . 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.
The Serdán-Oriental lacustrine basin in the eastern part of the Trans-Mexican Volcanic Belt holds... more 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, Der...
Abstract Paricutin volcano is the youngest and most studied monogenetic volcano in the Michoacán-... more Abstract Paricutin volcano is the youngest and most studied monogenetic volcano in the Michoacán-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&#39;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 1.68km³ 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.
Journal of Volcanology and Geothermal Research, 2017
Claus Siebe, Sergio Salinas, Lilia Arana-Salinas, José Luis Macías, James Gardner, Rosanna Bonasi... more Claus Siebe, Sergio Salinas, Lilia Arana-Salinas, José Luis Macías, James Gardner, Rosanna Bonasia The White Pumice (WP) is one of the thickest and most voluminous Plinian fallouts produced by Popocatépetl volcano in central Mexico during the Late Pleistocene-Holocene. Its eruption ~ 23,500 14C 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 km2, and has a volume of 10.4 km3. This gigantic landslide, characterized by exceptionally large proximal hummocks (&gt; 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 km2 was covered by &gt; 10 cm of pumice and ash. The total volume of the pumice fallout was estimated at ~ 1.9 km3 DRE (Dense Rock Equivalent). Pumice clasts are dacitic (62–66 wt.% SiO2, 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.% SiO2) magma was erupted effusively (4.4 km3, 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 km2 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 km3 (DRE) of juvenile magma (pumice and lava) were emitted and at least an additional ~ 10 km3 of pre-existing rocks (debris avalanche) mobilized. It surpasses in magnitude most other known Plinian eruptions from Popocatépetl 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 1759-1774 eruption of the Jorullo volcano in the Michoacán Guanajuato Volcanic field (MGVF), ... more The 1759-1774 eruption of the Jorullo volcano in the Michoacán 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 87 Sr/ 86 Sr
The Jorullo monogenetic volcano erupted 250 years ago at the southern border of the Trans-Mexican... more The Jorullo monogenetic volcano erupted 250 years ago at the southern border of the Trans-Mexican Volcanic Belt (TMVB), an area that records a long history of magmatic and tectonic activity. The oldest rocks that crop out in the area are early-Oligocene (32.7 ± 0.2 Ma) dioritic to granitic (60-72 wt.% SiO 2) plutons intruded by younger to contemporaneous (30.3 ± 0.1 and 33.3 ± 0.7 Ma) aplitic (76-78 wt.% SiO 2) dikes and mineralized veins. Volcanic rocks related to these intrusives form a thick sequence exposed in cliffs, from the base of which an altered andesite (58 wt.% SiO 2) was collected. The nearby epithermal Cu-mineralization of the Inguarán mining area to the southeast is also related to this Tertiary volcanic episode. The oldest expression of the TMVB in this area is represented by Pliocene (3.2-2.4 Ma) basaltic andesite to andesite (53-63 wt.% SiO 2) lavas (with pyroxene ± olivine) forming extensive mesas, eroded mounds, and thick elongate flows, that were unconformably deposited on top of the Oligocene rocks. Their emplacement was followed by erosion approximating a rate of 100 m/Ma over the past 3 Ma. This led to the formation of an inverted topography reflecting the higher resistance to erosion of these lavas that were originally deposited in valleys and today constitute prominent mesas. During the last 1 Ma, at least twenty-six monogenetic scoria cones formed in the study area, erupting about 10.2 km 3 of lava and pyroclastics dominantly composed of olivine and pyroxenebearing andesites (61 vol.% DRE), lesser basaltic andesites (30 vol.% DRE), and a minority of olivine-rich basalts (10 vol.% DRE). These eruptive products include the K-rich basaltic trachyandesites of Cerro La Pilita, a scoria and lava cone located close to Jorullo. The ≤ 27 ka San Hilario and Esmeralda lavas, which are located 13 km southeast of Jorullo, are the southernmost eruptive products of the TMVB and also the youngest volcanoes after Jorullo in this area. Mapping of main faults and scoria cone alignments on regional and local scales reveals that the ascent of dikes feeding Quaternary eruptions in the Jorullo area was controlled by westnorthwest and west-southwest basement structures, northeast-oriented subduction-related horizontal compressional stress probably associated with crustal fractures, and a major northwest-trending seismically active fault zone that passes near Paricutin and Jorullo.
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