Abstract

ANDRES DE PABLO, Nuria et al. Post-laharic evolution of a proglacial cannel: the Huiloac creek (Mexico). Bol. Soc. Geol. Mex [online]. 2014, vol.66, n.2, pp.305-328. ISSN 1405-3322.

In the last eruptive period of Popocatépetl volcano (19º 02'N, 98º 37' W, 5424 m) several syn-eruptive lahars modified the fluvial network of the northeastern slope, where the Huiloac River is located. The lahars that produced the most important morphological changes took place in 1997 and 2001. Although some explosive events have taken place since then, such as the recent eruptions of May and June 2013, lahars related to volcanic activity have not been recorded in Huiloac gorge. This article proposes a methodology to detect and quantify morphological changes and to determine the dynamics of erosion and sedimentary processes in a section of Huiloac gorgef or the first seven years after the syn-eruptive lahar of 2001. This method combines the interpretation of a temporal series of geomorphological maps and topographic profiles across the channel using CAD (Computer-aided design) and GIS (Geographic Information Systems). Finally, the analysis of the geomorphic and topographic evolution is cross-referenced with available information on rainfall. The results show that the initial phase (up until October 2002) is characterized by incision and removal of the material that filled the river bed during the 2001 lahar. Afterwards, the geomorphological action of running water and the dynamics of slopes widened and deepened the channel, although sedimentation occurred as well, as evidenced by river-banks and lahar terraces. The frequency and capacity of secondary lahars, fed by rainfall and glacier melt water, are the factors that determine the domain of erosion or sedimentation in Huiloac. Thus, it has been observed that in seasons with less rain and regular precipitation, fewer morphological variations occurred and a smaller amount of material was eroded, such as in the period 2004 ‒ 2006. On the other hand, exceptional rainfall in the dry season (January 2002 and January 2004) or continuous rains at the end of the wet season (September and October 2007) triggered processes of erosion by incision, lateral erosion, and removal of the laharic deposits. It can be concluded, at the end of this first period of observation, that despite considerable erosion, the riverbed is still unstable due to steep slopes on the sides of the river.

Keywords : Geomorphological mapping; lahars; GIS; CAD; Popocatépetl; Mexico.

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