Abstract

VAZQUEZ-RIOS, Mireya  and  FRANCO-RAMOS, Osvaldo. Dendrogeomorphic reconstruction of mass movements and lahars in Barrancas Seca and Ojo Salado, Pico de Orizaba, Mexico. Invest. Geog [online]. 2022, n.107, e60470.  Epub June 20, 2022. ISSN 2448-7279.  https://doi.org/10.14350/rig.60470.

Tree growth ring analysis has been used to spatially and temporally reconstruct geomorphological processes of the recent past in different geomorphic settings. In areas where there is forest, it is common for trees to be damaged by geomorphological processes, and these trees respond by disturbing the growth rings. The analysis of these disturbances provides information on the year of occurrence, dynamics, frequency and distribution of these processes. In such a way that trees are important natural archives and a reliable source of information, especially in places of difficult access where data is scarce or null, as in the case of several volcanic ravines in central Mexico. This research was carried out in the Seca and Ojo Salado ravines located northeast of the Pico de Orizaba volcano, where dendrogeomorphological methods were applied to analyze mass removal processes (landslides, rock falls) and lahars, using Pinus hartwegii , Pinus patula trees . and religious Abies. On the other hand, photogrammetric surveys were made in two sectors of the ravine with which high-resolution DEMs were built, which allowed the precise location of the sampled trees and a geomorphological interpretation of the study sites.

Regarding the results of the work, we identified that the number of disturbances in the trees due to mass removal processes was 29 and the most common were: impact scars (45%) and Tangential Rows of Traumatic Resin Ducts or TRD (21 %). In the case of lahars, the total number of disturbances was 70, and the most frequent were: TRD (61%) and impact scars (20%). The reconstruction of geomorphological processes was carried out from 1983 to 2018. In sector A, located at ~2800 masl, a landslide and the frequency of rock falls were analyzed. In sector B, located between 3,410-3,460 masl, slope processes were also studied, although special emphasis was placed on the reconstruction of lahars. In this altitudinal sector, lahars were also analyzed in the Ojo Salado ravine, which is a tributary of the main ravine. In sector A, 11 rockfall events were dated in the years: 1987, 1995, 2002, 2004-2007, 2011, 2014-2016. In sector B, six mass removal processes (1983, 2000-2001, 2003, 2015 and 2017) and 11 lahars (1983, 1988, 1991, 2000-2001, 2003, 2006, 2012, 2014-2015 and 2017) were identified. ). All the mass removal events in sector B coincide with the lahars in that same sector. In contrast, only three geomorphological processes coincided between sectors A and B in the years: 2006, 2014 and 2015. In addition, some lahars dated in the Barranca Seca (1983, 1991, 2000 and 2012) were also identified in its tributary the Barranca Salty eye. The results obtained confirmed the potential of Pinus hartwegii and Abies religiosa to carry out dendrogeomorphological analyses, and for the first time the potential of Pinus patula to study geomorphological processes was tested with satisfactory results, despite the growth problems it presented, since several fake rings. On the other hand, the events dated in this research coincide with the occurrence of other geomorphological processes dated in other volcanoes in central Mexico, which suggests that some of them could be triggered by regional factors such as hydrometeorological phenomena. For example, hurricanes and tropical storms that entered the Mexican territory along the Atlantic Ocean coast were identified as the possible triggers of five events (2005, 2011, 2014, 2012, 2017). In this way we conclude that dendrogeomorphology is a useful method to analyze geomorphological processes in forested areas, which represent a danger for human settlements, since in many cases they are exposed to phenomena controlled by climatic and/or geological forcing. Knowledge about the dynamics of the ravines and the frequency with which the analyzed geomorphological processes occur can contribute to the construction of natural hazard prevention plans in the area, taking into account that some communities such as Cuiyachapa and Cuiyachapa are located a few kilometers away. Tetelzingo. Also, this research can support the management of the Pico de Orizaba National Park and the next updates of the Management Program.

Keywords : dendrogeomorphology; rock falls; landslides; lahars; Pico de Orizaba.