Rain-Triggered Mass Movement Hazard Assessment of the 2025 Tejar Chimbo Landslide in Andean Ecuador
Journal
Highlights of Sustainability
ISSN
2696628X
Date Issued
2026-06-16
Author(s)
Banegas, Fredy
Salinas, Isela
Toulkeridis, Theofilos
Ordoñez-Fernandez, Jose
Chunga, Kervin
Type
Article
Abstract
The rainfall-triggered landslide that occurred at the Tejar site in Andean Ecuador on 27 April 2025 (12:35 p.m., local time), provides a representative case for understanding the interaction between extreme precipitation and volcanic geomaterials in slope instability processes. This study aims to characterize the geological and geotechnical conditions controlling the failure and to evaluate the mechanisms associated with rainfall-induced saturation in the Andean foothills of San José de Chimbo. Geological reconnaissance identified three main lithological units: cohesive laharic deposits, massive lapilli tuffs, and andesitic to ignimbritic volcanic rocks. Structural analysis revealed well-defined discontinuity planes, including joint systems and shear fractures with normal components, which extend several meters within the rock mass and act as preferential sliding surfaces. The methodology integrates field mapping, kinematic analysis, aerial photogrammetry, laboratory direct shear testing, and deterministic slope stability modeling using limit equilibrium methods. Additionally, historical precipitation records since 2010 were analyzed and correlated with intense rainfall associated with La Niña Modoki conditions. Results indicate that slope instability is primarily controlled by structurally guided planar failure mechanisms, significantly influenced by rock mass saturation and water infiltration along discontinuity planes. Back-analysis demonstrates that the factor of safety (FS) decreases from stable conditions (FS > 1.2) to values close to failure (FS ≈ 1.0) under fully saturated conditions, consistent with observed field behavior. The landslide evolved into debris flows with runout distances of up to 200 m and variable thicknesses. Based on these findings, mitigation measures including reinforced earth walls (e.g., Terramesh systems), slope regrading with berms, and deep anchoring elements were proposed, resulting in a significant increase in slope stability under both static and pseudo-static conditions. The proposed methodology provides a practical and transferable framework for rapid landslide assessment and mitigation in volcanic terrains, particularly in mountainous urban areas of the Andes and other regions with similar geological and climatic conditions. © 2026 Banegas et al.