Deslizamiento de tierras activo en Metztitlán, Hgo.

Abstract

From December 1991 to October 1992, an active landslide occurred near Metztitlan, Hgo. The town is located on a Hill formed by the debris of a large collapse that occurred during the Quaternary. The first active sliding occurred in December 1991 when several fissures appeared with a total length of 53 m. By May 1992 the fissures measured 263m and in October a total length of 1500 m had been reached. The landslide is rotational in several different blocks covering from the thalweg of Tlaxomotl stream to the main divide, separated by 6 main fractures parallel to the stream. At two locations the speed of opening of the fissures was measured from 0.3 mm/day to 3.3 mm/day, measured at 7 days intervals. A marl bed started sliding on top of an underlying shale bed; both strata are tilted towards the stream and are exposed by vertical erosion. This movement destabilized a mass of unconsolidated material with a volume of 850,000 m3, which resulted in the sliding of blocks over a 350m stretch of terrain. Over 30 houses have been damaged, and a XVI century convent is at risk. Vertical erosion by the Tlaxomotl underground water flow in the collapse debris, and human activities, arc the main factors that triggered the landslide process.