Kinematics of a Translational/Rotational Landslide, Central Andes, Northwestern Argentina

Abstract

The eastern foothills of the Central Andes, known as the Subandean Ranges, in Peru, Bolivia, and northwestern Argentina, are characterized by heavy rainfall, weakly cemented substrate rocks, thick regoliths, and bedding planes parallel to mountain slopes, features that create serious landslide hazards (Multinational Andean Project: Geoscience for Andean Communities, http://www.pma-map.com). A moderately sized landslide (the Termas Hill landslide) occurred in August 2003 on a slope of the Andean foothills in northwestern Argentina (Figure 1). The slide disrupted regolith and rock, leaving a steep-walled scarp and severing a 130-m-long segment of forest road. The sliding block travelled downslope a few tens of meters, undergoing fragmentation and torsion. On the basis of a topographic survey and structural evidence, this article discusses the geometry and kinematics of the Termas Hill landslide. Figure 1. Location maps. (A) South America with Argentina outlined and square representing inset B (TC = Tropic of Capricorn). (B) Salta Province (S = Salta City; RF = Rosario de la Frontera; TC = Tropic of Capricorn; open rectangle shows location of map in inset C). (C) Simplified geologic map overlaid on a Thematic Mapper satellite image (white rectangle represents area of landslide; x = campsite adjoining large pond; r = topographic ridge; f = reverse fault affecting Termas Hill landslide; Q = Quaternary deposits; A = Anta Formation, geology taken from Seggiaro and others, 1997). (D) Average rainfall between 2000 and 2005, inclusive; meteorological station located 30 km north from landslide site, in similar geomorphic and climatic situation. The Subandean Ranges in northwestern Argentina (22–26°S; Figure 1A and B) have a humid subtropical climate with annual precipitation of 700–1,200 mm and an average air temperature of 20°C. The climate is mild with a dry winter season. Rainfall is concentrated in the austral summer months and is of the monsoonal type (Figure 1D). The Subandean Ranges …