Vol.:(0123456789) 1 3 Environmental Earth Sciences (2022) 81:309 https://doi.org/10.1007/s12665-022-10382-0 ORIGINAL ARTICLE Integrated geophysical investigation for understanding agriculturally induced landslides in southern Peru Hanna E. Flamme 1  · Richard A. Krahenbuhl 1  · Yaoguo Li 1  · Brandon Dugan 1,2  · Jefrey Shragge 1  · Andrew Graber 3  · Dana Sirota 1  · Gavin Wilson 1  · Edgard Gonzales 4  · Javier Ticona 4  · Armando Minaya 4 Received: 16 June 2021 / Accepted: 3 April 2022 / Published online: 26 May 2022 © The Author(s) 2022 Abstract We conducted near-surface geophysical surveys in and around the Majes I agricultural development (60 km west of Areq- uipa, 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 refned 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 identifed 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 afected by signifcant human development. We integrated these results into updated landslide modeling. Our modeling for Majes I suggests stable con- ditions 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 food 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. Keywords Geophysics · Landslide · Agriculture · Modeling · Aquifer · Peru Introduction Majes is one of the largest and most important agricultural developments in the Arequipa region of southern Peru (Fig. 1). The agricultural development was established along the north–west ridge of the Siguas River Valley in the early 1980s atop one of the broad coastal plateaus, referred to as pampas, and it includes approximately 160 km 2 of irrigated land in an arid environment (Wei et al. 2021). The Majes development provides agricultural commodities to the sur- rounding region and contributes over US-$800 million to the Peruvian GDP per year (Gobierno Regional Arequipa 2016). To prepare for such a signifcant agricultural community in elevated desert plateaus, the Peruvian government began the construction of the Majes–Siguas irrigation project in 1971 to transport large volumes of water to the region. The irrigation project is one of the largest civil works in south- ern Peru, transporting approximately 34 m 3 /s of water over 100 km of aqueduct starting at Rio Colca and ending at the Siguas River (Gobierno Regional Arequipa 2016). From the Siguas River, water is moved through 16 km of canal to the Pampa de Majes, where it provides year-round support for agricultural crops including avocado, corn, onion, grapes, tomato, garlic, green beans, pepper, potato, paprika, and alfalfa (Huanca 2011; Gobierno Regional Arequipa 2016). Following the success of agricultural development at Majes I, the Majes–Siguas irrigation project soon will be expanded * Hanna E. Flamme hfamme@mines.edu 1 Department of Geophysics, Colorado School of Mines, Golden, CO 80401, USA 2 Hydrologic Science and Engineering Program, Colorado School of Mines, Golden, CO 80401, USA 3 Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, USA 4 School of Geophysical Engineering, Universidad Nacional de San Agustín de Arequipa, Arequipa, Peru