Lorenzo Vázquez-Selem

Late Quaternary Glaciation of Mexico

The glacial chronology of Mexico is based on glacial landforms of Iztaccihuatl (5,282 m a.s.l., 19°10′N, 98°40′W), Nevado de Toluca (4,558 m a.s.l., 19°08′N, 99°45′W), and La Malinche (4,461 m, 19°14′N, 98°00′W). Morphostratigra-phy, tephrochronology and 81 cosmogenic 36Cl exposure ages from Iztaccihuatl reveal new insights into the glacial sequence in Mexico. The most extensive recorded advance (Nexcoalango) occurred during Marine Isotope Stage 6 (MIS 6), probably at 195,000 BP and reached c. 3000 m. Iztaccihuatl lacks clear evidence of Wisconsinan glaciation prior to 20,000 cal yr BP. The local Late Pleistocene glacial maximum occurred after the climax of the Last Glacial Maximum (LGM). A first pulse (Hueyatlaco 1 advance) peaked at 20,000–17,500 cal yr BP and a second one (Hueyatlaco 2) at c. 17,000–14,000 cal yr BP. Valley glaciers reached to c. 3400–3500 m a.s.l. Recessional moraines developed from 14,000 to 13,000 cal yr BP, followed by a rapid glacier retreat at 13,000–12,000 cal yr BP. Subsequently, glaciers peaked again at c. 12,000 cal yr BP reaching c. 3800 m (Milpulco 1), and built recessional moraines until c. 10,000 cal yr BP. Then between c. 8300–7000 cal yr BP glaciers formed small but distinctive moraines above 4000 m a.s.l. (Milpulco 2). No evidence of glacier expansion has been found between Milpulco 2 deposits and the massive moraines of <1000 cal yr BP (Ayoloco) that occur at 4300–4700 m a.s.l. Possible correlations between the glacial record of Iztaccihuatl and other glacial sequences (La Malinche, Nevado de Toluca) are presented. The equilibrium line altitudes (ELA) of glaciers reveal ELA depressions for the five late Quaternary advances of 1030 m, 930 m, 730 m, 550 m and 250 m, respectively. The overall pattern of glaciation is similar to those of mid-latitude North America and tropical South America, thus supporting the general synchroneity of major climatic events. A temperature decrease of 5–9°C estimated from Hueyatlaco ELA supports marked cooling over tropical land and oceans during the LGM. Although inconclusive, evidence does not indicate glacier expansion during, but rather immediately following the Younger Dryas Chronozone. However, a global early-to-mid-Holocene event (8200 cal yr event) is coeval with Milpulco 2 advance, and the Ayoloco advance is contemporaneous with the Little Ice Age.

Mapping and modelling mass movements and gullies in mountainous areas using remote sensing and GIS techniques

Abstract Natural as well as human-induced mass movements and gullies are severe environmental hazards. Remote sensing data offer promising possibilities for identification and monitoring. But their effective use in mountainous areas is hampered by cloud effects and relief-controlled factors, which cause geometric distortions and shadow areas, among other constraints. Nevertheless, aerial photographs and satellite images (visible, infrared and microwave bands), or combinations thereof, have been successfully used to discriminate and delineate landslide and gully types. GIS modelling of mass movements and gullies, using ancillary information in combination with remote sensing data, is rapidly developing. The shortcomings of deterministic modelling of such chaotic phenomena as mass movements and gullies highlight the relevance of GIS-assisted approaches to exploratory and predictive modelling. This paper describes practical applications of remote sensing and GIS for mapping, monitoring, exploring cause-effect relationships and assessing hazards of mass movements and gullies in hilly and mountainous areas.

Orbital pacing and ocean circulation-induced collapses of the Mesoamerican monsoon over the past 22,000 y

The dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles, ocean circulation through its influence on atmospheric circulation, and sea-surface temperatures. However, few records from the summer North American Monsoon system are available to test for a synchronous response with other global monsoons to shared forcings. In particular, the monsoon response to widespread atmospheric reorganizations associated with disruptions of the Atlantic Meridional Overturning Circulation (AMOC) during the deglacial period remains unconstrained. Here, we present a high-resolution and radiometrically dated monsoon rainfall reconstruction over the past 22,000 y from speleothems of tropical southwestern Mexico. The data document an active Last Glacial Maximum (18–24 cal ka B.P.) monsoon with similar δ18O values to the modern, and that the monsoon collapsed during periods of weakened AMOC during Heinrich stadial 1 (ca. 17 ka) and the Younger Dryas (12.9–11.5 ka). The Holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation. We conclude that the Mesoamerican monsoon responded in concert with other global monsoon regions, and that monsoon strength was driven by variations in the strength and latitudinal position of the Intertropical Convergence Zone, which was forced by AMOC variations in the North Atlantic Ocean. The surprising observation of an active Last Glacial Maximum monsoon is attributed to an active but shallow AMOC and proximity to the Intertropical Convergence Zone. The emergence of agriculture in southwestern Mexico was likely only possible after monsoon strengthening in the Early Holocene at ca. 11 ka.

Multiple Dendrochronological Signals Indicate The Eruption Of Parícutin Volcano, Michoacán, Mexico

Abstract The eruption of Parícutin (1943–1952), a cinder cone volcano in Michoacán, Mexico, caused dendrochronological and dendrochemical responses that might be useful as general dating tools for eruptions. For the eruption period, pines near Parícutin have slightly suppressed ring widths plus high inter-annual variability of width. Wood anatomy changes include traumatic resin ducts and thin bands of false latewood. Dendrochemistry of tree rings shows little temporal variation in most elements, but beginning in 1943 sulfur content increased in rings of four trees and phosphorus content increased in rings of two trees. Hypotheses for increased S and P include new availability of pre-existing soil S and P and/or new input of S and P from the tephra itself. Pines at Parícutin also show suppressed ring widths for five years beginning in 1970, and had the eruption date not been known, the most likely conclusion from ring-width data alone would have been an eruption from 1970 to 1974. However, the 1970s suppression was in response to defoliation by a pine sawfly outbreak, not an eruption. For dendrochronological dating of cinder-cone eruptions, a combination of multiple characteristics (width, chemistry, and anatomy) would be more reliable than depending on any one characteristic alone.

Tree-ring reconstruction of past lahar activity at Popocatépetl volcano, Mexico

Lahars represent a major threat on the slopes of volcanoes all over the world. In order to realistically assess hazards, knowledge on the occurrence and timing of past lahar activity is of crucial importance. However, archival data on past events is usually scarce or completely missing. Tree-ring records have repeatedly proved to be a reliable data source for the reconstruction of past geomorphic events. However, tree rings have seldom been applied for the identification of past lahars. Therefore, it was the aim of this study: (i) to identify and describe disturbances in tree growth induced by well-documented lahar events and on this basis; and (ii) to recognise older, unknown lahar events with tree-ring analyses. Based on these goals, we collected 140 tree-ring series from 62 trees (Abies religiosa, Pinus hartwegii and Pinus ayacahuite) standing inside or adjacent to the lahar channel in the Huiloac gorge at Popocatépetl volcano, central Mexico. Most commonly, the known lahar events of 1997 and 2001 resulted in abrupt changes in tree-ring width as well as injuries. The same growth disturbances could be identified in the tree-ring series, indicating that five previously unknown lahar events would have occurred during the 20th century. Popocatépetl is one of the best surveyed volcanoes in the world and past eruptions are precisely noted in archives. As most of these unknown events occurred during periods with no volcanic activity, we believe that they were rainfall-induced rather than related to volcanic activity. In order to assess rainfall intensity threshold values for the triggering of events, the analyses of meteorological data needs to be integrated. In general, the investigated tree species proved to be highly suitable for the reconstruction of mass-movement processes. Therefore, the applied methods can be transferred to other locations where data on past events are missing.

Late Quaternary glaciations of Téyotl volcano, Central Mexico

Geomorphic and stratigraphic evidence of three glacial advances were found on the Late Pleistocene lavas of Teyotl volcano (4660 m), located in the Iztaccihuatl volcanic complex ( ca . 19 °N). The first glaciation (terminal moraines at 3400–3200 m) took place prior to 14,500 years BP. The second one (terminal moraines at 3800–4000 m) between 14,500 and 4800 years BP, apparently at the end of the Pleistocene. The third one (terminal moraines at 4060–4240 m) occurred after 4800 years BP, most likely around 2000 years BP. Small rock glaciers developed above 4300 m, probably during the Little Ice Age. Correlations are suggested with the glacial advances of other mountains of Central Mexico. Assuming that moist (and cool/cold) climates are responsible for glacial advances, the timing of glaciations is hypothesized in the light of existing palaeoecological records.

Geomorphic effects of the retreat of Jamapa Glacier, Pico de Orizaba volcano (Mexico)

ABSTRACTPico de Orizaba (5,700 m), on the eastern edge of the Transmexican Volcanic Belt, is an active volcano whose most recent eruption took place in 1687. Its summit is now covered by an ice cap from which several glaciers form. As on other mountains of central Mexico, the glaciers of Pico de Orizaba have retreated considerably during the past century and, in particular, during the last decades. This study focuses on the recent evolution of Jamapa Glacier, on the northern part of the mountain. It analyzes the geomorphologic processes in relation to the rapid retreat of the glacier snout and the intense periglacial activity on the valley sidewalls. The paper presents data on the thermic regime of ice cover deposits and their contrast with that of the glacier. At the end, it summarizes a model of the geomorphic evolution of the area below a retreating glacier.

Tree-ring based record of intra-eruptive lahar activity: Axaltzintle valley, Malinche volcano, Mexico

Abstract Lahars are a widespread phenomenon in volcanic environments and good knowledge generally exists on contemporary, syn-eruptive lahar activity. Much less data is, by contrast, available on post-eruptive lahars and/or hydrogeomorphic processes out of extinct volcanic complexes. In this study we present a reconstruction of intra-eruptive lahar activity in Axaltzintle valley (Malinche volcano) using growth-ring records of 86 Abies religiosa trees. Based on the identification of 217 growth disturbances, field evidence and hydrological records we reconstruct a total of 19 lahars for the period 1945–2011. The reconstructed lahars were mostly triggered by moderate intensity, but persistent rainfalls with sums of at least ~100 mm. By contrast, the 1998 and 2005 lahars were presumably triggered by hurricane-induced torrential rainfalls with >100 mm in three days.

History of pedogenesis and geomorphic processes in the Valley of Teotihuacán, Mexico: Micromorphological evidences from a soil catena .

Este trabajo proporciona nuevas evidencias sobre la historia edafologica y geomorfologica en el Valle de Teotihuacan, Mexico. El paisaje del suelo en este lugar esta formado por un Luvisol y un “suelo negro”, cuyos analisis micromorfologicos permitieron: (a) distinguir entre procesos in situ y procesos heredados, y (b) establecer las relaciones espaciales de erosion/sedimentacion a traves de una catena de tres perfiles de suelo. La seleccion de los suelos se realizo a partir de fotointerpretacion y posterior verificacion de una toposecuencia que mostraba una distribucion desde ladera media hasta piedemonte coluvial. Las muestras de estos perfiles fueron caracterizadas de manera fisico-quimica, incluyendo la observacion micromorfologica de laminas delgadas con microscopio petrografico. Los resultados obtenidos se resumen en las observaciones geomorfologicas, la descripcion y el analisis de los perfiles de suelo de la catena Zacatlan, y los resultados micromorfologicos. El conjunto permitio interpretar y reconocer tanto los procesos edafogeneticos actuales como los heredados debidos al transporte por erosion de suelo en epocas pasadas. En el “suelo negro” los procesos clave son el desarrollo de propiedades verticas, la humificacion y la acumulacion de carbonatos secundarios; la micromorfologia tambien revelo fragmentos de arcilla iluviada y nodulos de hierro redepositados. En el Luvisol domina la iluviacion de arcilla asociada con procesos redoximorficos. En los horizontes verticos se observo la presencia de fragmentos de pomez fuertemente meteorizados coexistiendo con fragmentos de roca y minerales con debil meteorizacion. Los edaforrasgos del “suelo negro” difieren fuertemente de los del Luvisol, lo cual permitio reconocer rasgos heredados del Luvisol en los horizontes del “suelo negro”. Por lo tanto, las observaciones micromorfologicas nos permiten proponer que el “suelo negro” probablemente incorporo materiales del Luvisol, los cuales fueron anteriormente coluviados. La presunta fase de erosion puede corresponder con una aridizacion climatica.

Régimen histórico de incendios y su relación con el clima en un bosque de Pinus hartwegii al norte del estado de Puebla, México

El bosque de Pinus hartwegii en el ejido Rinconada, municipio de Chignahuapan, representa la region de mayor incidencia de incendios forestales en el estado de Puebla. Con el objetivo de reconstruir la historia del fuego y determinar su asociacion historica con el clima, se tomaron 43 muestras con cicatrices de incendios y se analizaron con base en tecnicas dendrocronologicas; de 40 muestras, se lograron datar 235 cicatrices de incendios. Se reconstruyo la historia del fuego para el periodo 1876-2011 (136 anos). El 91,7 % de los incendios se registro en la estacion de primavera y el 8,3 % en verano. El intervalo medio de incendios (MFI, por sus siglas en ingles) y el intervalo de la mediana de probabilidad de Weibull (WMPI, por sus siglas en ingles) al considerar todas las cicatrices fue de 5,6 y 5,0 anos, respectivamente; mientras que para los incendios mas grandes o extensos cuyas cicatrices se registraron en el 25 % de las muestras o mas, los valores de MFI y WMPI fueron de 9,2 y 8,5 anos, respectivamente. La presencia de incendios fue continua hasta la primera decada del siglo XXI; sin embargo, posterior a 1988 se observo una disminucion en su frecuencia. Se determino una relacion positiva entre la disminucion de la precipitacion (sequia) y la ocurrencia de incendios. De igual manera, valores negativos de NINO 3 y PDSI, asociados a condiciones de sequia, han influido positivamente en la modulacion de la frecuencia historica de incendios en esta region del centro de Mexico.