Physical-mechanical behavior of fresh and completely altered rocks as an important factor of slope instability in the El Rosario Monarch Butterfly Sanctuary, Michoacán, Mexico

Slope instability in the Butterfly Biosphere Reserve (RBMM) Michoacán, Mexico, is a widespread phenomenon that results from the complex interaction among different factors such as climate, slope, and the spatial distribution of different rock units. The climate is temperate subhumid, with rains in summer and an annual average rainfall of 700 to 1250 mm. The main physiographic units of the area are volcanic mountains, with slopes greater than 30 degrees. The main scope of this study is to characterize the physical-mechanical properties of fresh and completely altered lower Miocene andesitic lavas of the Sierra de Angangueo (Cerro El Campanario, province of El Rosario, Michoacán) by implementing laboratory tests (bulk density, permeability, porosity, uniaxial compressive strength). The fresh rock sample presents total porosity, permeability, and UCS values of 0.262 mD, 17.1 %, and 63.5 MPa, respectively. Instead, the altered rock display values of 393.71 mD, 60.9 %, and 0.26 MPa. Our results suggest that the slope and the degradation of the rock properties induced by alteration are the conditioning factors of instability in the region. Atypical rainfalls may act as triggering mechanism for slope failure.