Vol 60, Núm.. 2, 2008, p. 187-201

Mechanical instability quantification of slopes at Cofre de Perote volcano, eastern Mexico

Cuantificación de la inestabilidad mecánica en pendientes del volcán Cofre de Perote, México oriental

Rodolfo Díaz Castellón1 ,*, Gerardo Carrasco Núñez2, Alfonso Álvarez–Manilla Aceves1 , 3

1 Posgrado en Ciencias de la Tierra Centro de Geociencias Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Qro. 76230
2 Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Qro. 76230.
3 Dirección de Estudios de Posgrado de la Facultad de Ingeniería, Universidad Autónoma de Querétaro, Ciudad Universitaria, Cerro de las Campanas s/n, Querétaro, Qro. 76010.

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Cofre de Perote (CP) volcano is located at the eastern end of the Trans–Mexican Volcanic Belt (TMVB) at 19°30' Lat N, 97°10' Long W. At a height of 4,282 m.a. s.l, it comprises one of the most massive structures within the Citlaltépetl – Cofre de Perote volcanic range (CCPVR), which constitutes an important physiographic barrier that separates the central altiplano, also known as Serdán Oriental, from the coastal plains of the Gulf of Mexico. This massive structure has repeatedly collapsed, and at least two of the collapse events occurred long after activity ceased, suggesting that even extinct volcanoes may pose an important hazard to nearby populated areas. In the present work, volcanic instability is approached through both quantitative and descriptive methods that include combined numerical analysis of limit equilibrium, calculated with Bishop's modified method, and finite element analysis. The combined techniques were applied after attaining mechanical parameters in the laboratory, the field and through careful geological observations in order to obtain a model that approaches structural conditions prior to the destruction of the volcano.

Reconstruction of the ancient volcano was used to propose an instability model for the modern summit, where maximum stress/ strain relationships before failure were determined for the reconstructed section and actual volcano summit. Results obtained from these models indicate that the volcanic edifice is still unstable, could experience failure in the near future, and should be considered for future hazard assessment.

Key words: volcanic instability, Cofre de Perote, quantitative assessment, inactive volcanoes.