Geological Setting, Volcanic Stratigraphy, and Flank Failure of the El Estribo Volcano, Pátzcuaro (Michoacán, Mexico)

Abstract

The El Estribo Volcano is located within the Michoacán–Guanajuato Volcanic Field in western México. Previous works have considered this volcano as a single cinder cone. The results of this study, however, suggest that it consists of a basal shield volcano crowned by a cinder cone. The upper cinder cone has a 1.2 km base and a 0.5 km crater with a maximum altitude of 2450 m a.s.l. The shield volcano has a basal diameter of 3.6 km and it is cut by an E–W-oriented normal fault. Several landslides have been triggered at the fault scarp, resulting in debris avalanche deposits being emplaced to the north into Lake Pátzcuaro. A refined stratigraphy of El Estribo Volcano comprises three main lithological units (Flv-la, E-Sh, and E-Ci): (1) three different sequences of lacustrine and ash layers with ages >30,000 yr, 10,000–30,000 yr, and <3000 yr, respectively (Flv-la); (2) basaltic–andesitic lava flows of the shield volcano (E-Sh); and (3) stratified scoria falls, reworked beds, and scoria falls interbedded with pyroclastic surge deposits (E-Ci) covering a palaeosol dated at 28,360 ± 170 yr BP (Ps). The southern shore of Lake Pátzcuaro is characterized by at least two debris-avalanche deposits, with marked differences in morphology. The first one, dated at 28,000 yr BP, presents an emplacement length of 3.2 km and a height/length (H/L) ratio of 0.06. The second one, dated at 14,000 yr BP, has a maximum run-out of 2 km and an H/L ratio of 0.08. The causes of these collapses are still under study and may involve the operation of different factors, such as: (i) destabilization during the emplacement of the cinder cone; (ii) different rock strengths between the involved rocks and sediments; (iii) seismic events; and (iv) slope instability.