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Failure conditions and triggers of the Achoma landslide, central Andes region, Arequipa Peru
Lemus, Oscar Santi, Paul M. (Paul Michael), 1964- Colque, Percy Meza, Pablo Salas, Guido
Lemus, Oscar
Santi, Paul M. (Paul Michael), 1964-
Colque, Percy
Meza, Pablo
Salas, Guido
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2023-04
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Abstract
The Colca River valley in southern Peru is the longest waterway of the Pacific Peruvian hydrologic basins, starting in the PerĂº Altiplano, and crossing the western Andean Cordillera to the Pacific Ocean. The area has been regularly impacted by large landslides of the valley slopes, and geologic evidence documents intense, recurrent, and catastrophic events, like landslides, debris avalanches, and floods. On June 18, 2020, more than 5,400,000 m3 of soil and weak rock slid into the Colca River valley near the town of Achoma. The rotational slide involved 40 hectares of land that was displaced 500 meters. The event destroyed the agricultural land, impacting the economy of many families, and the displaced material over the Colca River created a dam that increased the risk of flooding for the towns upstream. The exact factors that led to the landslide in Achoma, including triggering factors, are uncertain. The activity of farms, most of which are currently irrigated or have been irrigated in the past, and the presence of a large water transportation canal upslope of the landslide are the most likely causes of the increase in ground-water levels leading to failure. The purpose of this work is test various groundwater and infiltration scenarios to estimate the amount of water involved in the destabilization and triggering of the Achoma landslide, using numerical simulation of changing groundwater conditions. While not definitive, our early work indicates that, even though the landslide occurred during the dry season and before the irrigation began for the year, we cannot yet rule out irrigation as a contributing factor. On the other hand, increasing ground-water levels from leakage from the water conveyance canal appears to be a necessary component to cause slope failure.
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