Resumo

CASTILLO, Miguel; MUNOZ-SALINAS, Esperanza  e  ARCE, José Luis. Assessment of the fluvial erosive system in the Popocatépetl volcano (Mexico) by means of morphometric analysis. Bol. Soc. Geol. Mex [online]. 2015, vol.67, n.2, pp.167-183. ISSN 1405-3322.

Fluvial systems are sensitive to changes in tectonics, volcanic processes, climate and lithology. These factors can modify the erosion rates producing changes in the topography of mountains, channels and hillslopes. The analysis of the longitudinal profile of rivers and the morphometry of river basins are powerful tools that allow the detection of both tectonic and climatic signals and also allow the detection of zones presenting lithologies with a high degree of resistance to erosion. Most of the studies in landscape evolution have been focused on mountain settings driven by active tectonics. The study of stratovolcanoes has, however, received less attention although they are an important part of mountainous reliefs, specially in central Mexico. Here we analyze the stream long profiles of the Popocatépetl volcano (n = 12) and the morphometry of its river basins (n = 11) with the aim to obtain the quantitative data of relief and explore the relation between the mountain topography and the erosion due to fluvial processes. Our results indicate that both the normalized channel steepness index (k_sn) and stream power (AS) increase at the transition between the mountain area and piedmont. The erosion rates are particularly high downstream of headwaters. We detected the presence of knickpoints (n = 19), which in most of the cases, are generated at the front of lava flows. We found a moderate correlation (R² = 0.51; n = 11) between the distance of knickpoint retreat and the drainage area and a weak to moderate correlation (R² = 0.38) between the retreat rate and the drainage area. Our results suggest that the age and resistance of lavas to erosion control the rates of knickpoint recession which has a mean of 0.05 ± 0.02 m yr^-1. The river basin morphometry indicates that the hillslope morphology is not tightly related to fluvial incision. Nevertheless, the channel incision rates are high in most of valleys of the study area. We conclude that the fluvial system is in disequilibrium, probably due to the continuous volcanic activity of Popocatépetl volcano.

Palavras-chave : longitudinal profile of rivers; river basin morphometry; knickpoints; Popocatépetl volcano.

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