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Small event, big impact : insights from Vallunaraju cascade event on April 28, 2025, Cordillera Blanca, Peru
Glacial lake outburst floods (GLOFs) are sudden releases of water from glacier-fed lakes. They can be triggered by a range of processes, including ice or rock avalanches, moraine failures, etc, and are recognized as among the most destructive cryospheric hazards.
a) Regional context showing the glacier and lakes inventory and documented GLOFs in the Cordillera Blanca (Peru) ; b) Enlarged view of the Casca valley, Vallunaraju glacier and flood path to the Independencia district. c) Pléiades RGB imagery (true-colour composite, bands 1 2 3) showing the source area before and after the event (©CNES/AIRBUS). The urban extent was updated for the year 2025 using the Pleiades image, on the basis of the OpenBuildings dataset (v.3).
a) Reconstructed GLOF dynamics from Lakes A and B to the beginning of the Independencia district. Red-blue colorbar shows local sediment yields rates (m³/m) averaged each 50 m. a1) Field photo of the deposit cone (4,290 m a.s.l.) caused by the GLOF in the foreground, and the strong erosion of the pre-existing cone in the background ; a2) Aerial photo at the outlet of section E’–F’ showing traces of erosion and deposition between ; a3) Erosion and deposition in the Independencia district ; a4) Photograph of the first depositional area (4,290 m a.s.l.) showing remnants of fine sediments after the GLOF event. b) Volumetric sediment quantification for GLOF propagation along the 14 km river channel. Alpha (α) shows the average slope (in percentage) of the drawn black line.
In the Cordillera Blanca, Peru, one of the world’s best-documented GLOF regions, most studies and risk-management strategies have historically focused on large glacial lakes (>0.1 km²), mainly because they store larger volumes of water and have often been associated with catastrophic events. However, small and medium-sized lakes (<0.1 km²) are far more numerous in many deglaciating mountain ranges and remain frequently underrepresented in hazard assessments.
In this study, we reconstructed the 28 April 2025 Vallunaraju GLOF in the Cordillera Blanca, Peru. The event was triggered by a rockfall that impacted two small periglacial lakes (< 0.01 km²) in the upper Casca Valley. Using very-high-resolution Pléiades satellite imagery and digital surface models (including acquisitions supported through CIEST²) we quantified the source-area changes, downstream erosion, and sediment entrainment along the flood path. Documented impacts included two fatalities and damage to five bridges, twenty-nine houses and water infrastructure. Although the initial lake-water release was modest, approximately 42×10³ m³, the flood progressively entrained sediment along its 14 km path toward the Huaraz–Independencia conurbation. This process amplified the total moving mixture to approximately 296×10³ m³, about 6–7 times the initial lake volume. Depending on plausible drainage scenarios, entrained sediment accounted for 73–84% of the total mixture volume, whereas lake water contributed 13–15% and background discharge ∼1–5%. These results demonstrate that downstream erosion and sediment availability controlled the magnitude of the event more than the initial lake volume itself.
The Vallunaraju sediment-amplified cascade highlight a critical gap in current GLOF assessments : the need to integrate trigger susceptibility, downstream propagation, sediment entrainment, exposure, and social vulnerability. Such an integrated perspective is essential to better anticipate emerging risks in rapidly changing mountain environments.
In this study, we reconstructed the 28 April 2025 Vallunaraju GLOF in the Cordillera Blanca, Peru. The event was triggered by a rockfall that impacted two small periglacial lakes (< 0.01 km²) in the upper Casca Valley. Using very-high-resolution Pléiades satellite imagery and digital surface models (including acquisitions supported through CIEST²) we quantified the source-area changes, downstream erosion, and sediment entrainment along the flood path. Documented impacts included two fatalities and damage to five bridges, twenty-nine houses and water infrastructure. Although the initial lake-water release was modest, approximately 42×10³ m³, the flood progressively entrained sediment along its 14 km path toward the Huaraz–Independencia conurbation. This process amplified the total moving mixture to approximately 296×10³ m³, about 6–7 times the initial lake volume. Depending on plausible drainage scenarios, entrained sediment accounted for 73–84% of the total mixture volume, whereas lake water contributed 13–15% and background discharge ∼1–5%. These results demonstrate that downstream erosion and sediment availability controlled the magnitude of the event more than the initial lake volume itself.
The Vallunaraju sediment-amplified cascade highlight a critical gap in current GLOF assessments : the need to integrate trigger susceptibility, downstream propagation, sediment entrainment, exposure, and social vulnerability. Such an integrated perspective is essential to better anticipate emerging risks in rapidly changing mountain environments.
This work was made possible through a strong collaboration between OSUG laboratories in France, including ISTerre, IGE, and EDYTEM, and key Peruvian partners, including Universidad Nacional Santiago Antúnez de Mayolo (UNASAM), Instituto Nacional de Investigación en Glaciares y Ecosistemas de Montaña (INAIGEM), Autoridad nacional del Agua (ANA), and Instituto Geológico Minero y Metalúrgico (INGEMMET).
The full study is published in : NATURE, npj Natural Hazards
Fundings : CNES (post-doctoral scholarships) ; CNRS (PAPROG, Labcom) ; Prociencia-Concytec (Péru)
Fundings : CNES (post-doctoral scholarships) ; CNRS (PAPROG, Labcom) ; Prociencia-Concytec (Péru)
References :
Cusicanqui, D., Loarte, E., Gómez, W. et al. Small event, big impact : insights from Vallunaraju cascade event on April 28, 2025. npj Nat. Hazards 3, 51 (2026).
Scientific contacts :
- Diego Cusicanqui – ISTerre, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, Univ. Gustave Eiffel, Grenoble, France