Geophysical Characterization of Moraine Deposits at Uspaccocha Glacial Lake (Apurímac, Peru): Implications for Moraine-Dam Stability Assessment

This study focuses on the internal structure and hydrogeological behavior of the moraine dam retaining Uspaccocha glacial lake, a high-mountain glacial system located in the tropical Andes of southern Peru. Accelerated glacier retreat in the region has increased the susceptibility to glacial lake outburst floods (GLOFs), one of the main glacier-related hazards in high-mountain Andean environments.

Vertical Electrical Sounding (VES), Seismic Refraction (SR), and Multichannel Analysis of Surface Waves (MASW) were jointly applied to characterize the subsurface geometry, lithological variability, and mechanical conditions of the moraine deposits. The surveys revealed a complex subsurface sequence composed of a shallow, poorly consolidated till layer ranging from 7 to 20 m in thickness, overlying a more compact basal till reaching thicknesses of up to 45 m. The underlying limestone-related bedrock was identified at depths ranging from 27 to 80 m.

Correlations between intermediate resistivity values and seismic velocity distributions revealed a discontinuous and irregular groundwater level consistent with the chaotic nature of the moraine deposits. These observations indicate that lithological heterogeneity and subsurface water flow strongly control internal permeability and potential instability processes within the moraine dam.

The integrated geophysical approach allowed for a detailed characterization of subsurface conditions within the moraine dam, particularly the distribution of saturated zones and lithological variability. At Uspaccocha, the observed lithological variability and irregular groundwater distribution suggest that subsurface conditions may influence slope instability and internal erosion processes. The findings highlight the need for continuous monitoring and multi-hazard assessments in response to the increasing impacts of glacier retreat in the tropical Andes, while also demonstrating the value of integrated geophysical characterization for understanding the internal dynamics of moraine dams.