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Failure conditions and triggers of the Achoma landslide, central Andes region, Arequipa Peru
Alarcon, Oscar
Alarcon, Oscar
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2023
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2024-11-29
Abstract
The Colca Valley has historically been subject to a variety of geological hazards such as landslides, rock falls, and debris flows. On June 18, 2020, a rotational landslide occurred near the community of Achoma in the Colca Valley. The event destroyed agricultural land, impacting the finances of many families, and the displaced material crossed the Colca River and created a dam that increased the risk of flooding for the towns upstream.
To estimate the critical groundwater conditions that caused the Achoma landslide, limit equilibrium and finite element analyses were completed. Also, forward modeling was completed to analyze the hazard posed by further movement of the scarp. The research relied on two-dimensional models that required several kinds of information to provide valid results. At the Achoma site, the information on the strength of in situ soil and rock materials and the depth and distribution of groundwater is extremely limited and the access to the zone is restricted and dangerous. Therefore, remote sensing data was used to inform these parameters, accompanied by probabilistic analysis. The use of satellite images, drone images, and three-dimensional models was also vital to complete the research.
The slope stability was dependent on lacustrine sediments composed of clayey silts interbedded with sandstones and conglomerates of the Colca formation. The trigger of the landslide was a combination of natural and anthropogenic factors which produced changes in the groundwater levels. The principal causes identified are rainfall, extensive irrigation activity on the landslide area, and potential leakage from an irrigation project conformed by a canal and tunnel uphill from the landslide.
Considering the results, we observed differences in the influence of the different triggering mechanisms. The impact of the rainfall was low to moderate because almost no rain occurred two months before the landslide. The agricultural activity in the area has a moderate influence because the irrigation could result in excess water percolation to the perched water table. And finally, the effect of the Majes-Siguas canal and tunnel observed was moderate-high. Models results show that the leakage from the tunnel is more likely than leakage from the canal.
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