Morphology, structure and kinematics of a rainfall controlled slow‐moving Andean landslide, Peru

Abstract

The large slow‐moving landslide of Maca is located in the upper Colca valley (southern Peru), a region characterized by a well pronounced rainy period, and intense and recurrent sustained seismicity. The landslide, developed in deep lacustrine deposits, has recently accelerated, threatening the Maca village. This work aims at understanding the rupture mechanism and the causes of the recent landslide reactivation/acceleration. We present a multidisciplinary characterization of the Maca landslide that includes: (i) geological and morphological mapping in the field; (ii) remote sensing analysis using an historical aerial photograph of 1955 and the Pléiades satellite images (2013); (iii) global positioning system (GPS) including time‐series of surveys over 13 years, and continuous measurements over 14 months; (iv) a geophysical campaign with deep electrical resistivity tomography profiles acquired across the landslide mass. Our study shows that this 60 Mm3 landslide, which can be classified as a clay/silt compound landslide, moved by 15 m between 2001 and 2014 with a large inter‐annual velocity variation (up to a factor of 500) depending on the rainfall intensity. We suggest that these dramatic changes in velocity are the result of the combination of a threshold mechanism and the short intense rainy season in Peru. This study reveals three main driving factors acting at different timescales: (i) over several decades, the river course has significantly changed, causing the Maca landslide reactivation in the 1980s due to the erosion of its toe; (ii) at the year scale, a minimum amount of rainfall is required to trigger the motion and this amount controls the landslide velocity; (iii) transient changes in slide velocity may occur anytime due to earthquakes. This study particularly highlights the non‐linear behaviour of the motion with rainfall. Copyright © 2016 John Wiley & Sons, Ltd.

Rain and small earthquakes maintain a slow-moving landslide in a persistent critical state

“…1 and Supplementary Fig. 1) has been identified has a clay/silt compound slide with a rupture surface of uneven curvature 24 and thus, belongs to the soil slide category 25 . This 60 million m 3 landslide impacts a village in a rural area in the Colca Valley, southern Peru, in a very seismically active zone 26,27 .…”

Self‐Entrainment Motion of a Slow‐Moving Landslide Inferred From Landsat‐8 Time Series

“…As a consequence, the study of slow-moving landslides may lead a better understanding of the physical processes governing both slow and rapid landslides (Palmer, 2017). In recent years, various studies of slow-moving landslides (e.g., Bennett et al, 2016;Handwerger et al, 2013Handwerger et al, , 2015Hsu et al, 2014;Iverson & Major, 1987;Lacroix et al, 2014Lacroix et al, , 2015Reid, 1994;Schulz et al, 2009;Zerathe et al, 2016) have revealed a rich diversity in kinematics, with various forcing factors, for example, rainfall, earthquakes, glacial retreat, and anthropogenic activity. These forcings act over a wide variety of timescales, from seconds (earthquakes Lacroix et al, 2014) to several decades (glacial retreat Strozzi et al, 2010), thus making their study challenging.…”

“…Landslide motion is often interpreted to occur as a direct consequence of external forcing factors (e.g., Handwerger et al, 2013Handwerger et al, , 2015Hsu et al, 2014;Lacroix et al, 2014;Reid, 1994;Zerathe et al, 2016), such as rainfall or ground shaking (i.e., from earthquakes). However, different internal processes may also influence landslide motion; for example, progressive failure is thought to play a key role in the initiation of landslide motion (Amitrano, 2004;Carey & Petley, 2014;Eberhardt et al, 2004;Gischig et al, 2016;Lacroix & Amitrano, 2013).…”

A micromechanical model of rate and state friction: 1. Static and dynamic sliding

“…One obvious reason is an applied normal stress much lower than for tectonic faults or laboratory experiments (typically of the order of 10–100 MPa) so that very few contacts reach the plastic limit, an effect enhanced for smoother surfaces. This would be consistent with the fact that the interface of the Maca landslide studied in [ Lacroix et al , ] is about 70 m below the surface [ Zerathe et al , ]. Assuming a rock density of 3000 kg/m 3 , this corresponds to a lithostatic pressure of about 2 MPa, 1 or 2 orders of magnitude lower than typical normal stress in laboratory experiments.…”