IANIGLA   20881
Unidad Ejecutora - UE
congresos y reuniones científicas
Inventory of landslides at the Santa Cruz river basin (San Juan, Argentina) and its relationship with the Andean cryogenic environment
Congreso; XI. International Conference On Permafrost; 2016
In mountainous areas as the Andes it is common to see mass removal processes produced at different scales, levels of activity and speed. Several authors have also reported that in regions underlain by permafrost there is the development of a special type related to the active layer which can occur when there is loss of shear strength, this process is called active layer failure.The objective of this work is to identify and characterize the different types of landslides in the upper stretch of the Santa Cruz River basin in the Central Andes in the province of San Juan, Argentina on the assumption that they have a trigger mechanism linked to cryogenic processes.The Santa Cruz River basin of 432 km2 is located between 31 ° 44´ to 31 ° 55´ S and 70 ° 11´ and 70 ° 28´ W in the province of San Juan, Argentina. In the region there are abundant periglacial landforms and processes, as well as indicators of landslide processes. Seismic events related to those indicators are discarded because most of those events have their hypocenter more than 100 km of distance from the studied region and from 1985 to the present, no data related to removal processes are recorded as mass triggered by earthquakes (Penna et al., 2013).Based on the digital analysis of high-resolution images, 39 rock- and / or debris slides, translational, rotational movements and composite bodies were identified. Extraction of topographic parameters from a digital elevation model also allowed the quantification of topographic determinants for each of them. It was found that the average height of the crown is 3900 m and 3500 m was the altitude at the foot. The average slope of the detachment is 23° and in the sector of the resulting body it is 17°. The total length measured between the crown and the foot varies between 165 and 2850 m while the detachment scar is between 18 and 240 m. The displaced masses are between 30-4150 m wide and 120-2700 m long. The total area involved in the landslide represents 4.3% of the surface of the basin.The identified bodies also show a major lithological and geometric control, since they occur mainly in continental environment with sedimentary lithologies or on very weathered igneous rocks, on slopes with unfavorable orientations. Fundamentally, the landslides zones as well as the deposits are located on slopes facing W, W-SW and W-NW. These orientations represent the most vulnerable hillsides, unprotected by the surrounding relief itself and receive a higher rate of global solar radiation throughout the year. Although there are no chronological datings of the studied deposits, based on geomorphological criteria they can be classified as inactive deposits and their estimated age can range from 100 to 5000 years (BP).It is to add that the average altitude of the failure crowns is closely similar to the average altitude of the annual isotherm 0 °C and the lower limit of mountain permafrost in situ (without creeping). An important effect of permafrost is to stabilize slopes, increasing the resistance to the shear angle; however, an increase in the amount of moisture in the active layer or supra permafrost layer can contribute to reducing the resistance of the granulometric sedimentary material and trigger detachments. Haerberli (1992) indicated that an increase in air temperature produces not only degradation of permafrost but also slope instability in glacial and periglacial regions. This work proposes the degradation of Andean permafrost in San Juan linked to the increase of temperature within the climatic variability of the Holocene as a possible trigger for landslides.BibliographyHaeberli, W., 1992. Construction, environmental problems and natural hazards in periglacial mountain belts. Permafrost and Periglacial Processes 3 (2), 111-124.Penna, I., Derron, M.H., Volpi, M. and Jabodeyoff , M., 2013. Analysis of past and future dam formation and failure in the Santa Cruz River (San Juan province, Argentina). Geomophology, vol. 186: 28-38