Integrated geophysical investigation for understanding agriculturally induced landslides in southern Peru

We conducted near-surface geophysical surveys in and around the Majes I agricultural development (60 km west of Arequipa, Peru), where the nexus of geology and agriculture has increased landslide activity along the Majes–Siguas River Valley. Through DC resistivity, transient electromagnetics (TEM), and seismic surveys, we refined the understanding of local geology, characterized the agricultural impact on the local water table, and updated landslide modeling to help inform discussions on landslide mitigation strategies at Majes I and landslide prevention at the planned Majes II site. At the Majes I development, we identified an increase in water table and water saturation due to irrigation. At the planned Majes II site, which shares similar geology to Majes I, we interpret the regional water table that has yet to be affected by significant human development. We integrated these results into updated landslide modeling. Our modeling for Majes I suggests stable conditions prior to irrigation; as the water table rose from irrigation, landsliding began and evolved as a retrogressive failure that is now focused along the headscarp near critical infrastructure including the Carretera Panamericana (Pan-American Highway). Majes II is currently stable and irrigation management, such as drip versus flood techniques, must be supported. Soil ameliorants such as polymers and/or biochar should be encouraged to hold water near the roots to reduce the risk of landslide initiation. Combined this work shows the value of integrated hydrological and geophysical research for landslide management and optimized irrigation.