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<p>The Cordillera Blanca (Peru) is among the world’s best documented GLOF regions. Yet hazard prioritisation frameworks still focus mainly on large lakes (&gt;0.1 km²), while the numerous small (&lt;0.01 km²) and medium (0.01–0.1 km²) lakes remain comparatively underassessed. In Huascarán National Park, 67% of the 882 inventoried lakes are small and 26% are medium-sized. In this study, we reconstruct the 28 April 2025 Vallunaraju cascade event in the Casca valley, where a rockfall impacted two small lakes and triggered an outburst flood reaching the Huaraz–Independencia conurbation 14 km downstream. Documented impacts included two fatalities and damage to five bridges, twenty-nine houses and water infrastructure. Although the modest initial lake-water release (~42 × 10<sup>3</sup> m<sup>3</sup>), progressive channel-bed entrainment increased the total moving mixture volume by ~6–7 times to 296 × 10<sup>3</sup> m<sup>3</sup>. 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%. We interpret Vallunaraju as a sediment-amplified cascade showing that small-lake outbursts can generate severe downstream consequences where triggers, abundant erodible sediment and exposure coincide, supporting integrated assessments that include small lakes, trigger susceptibility and propagation and exposure controls.</p>

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Small event, big impact: insights from Vallunaraju cascade event on April 28, 2025

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月28日

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  • Diego Cusicanqui,
  • Edwin Loarte,
  • Wilson Gómez,
  • Hilbert Villafane,
  • Kristen L. Cook,
  • Guillaume Piton,
  • Benjamin Lehmann,
  • Florence Magnin,
  • Adina E. Racoviteanu,
  • Swann Zerathe,
  • Simon Filhol,
  • Katy Medina,
  • Rolando Cruz,
  • Ronald Concha,
  • Juan C. Torres-Lázaro,
  • Pascal Lacroix

摘要

The Cordillera Blanca (Peru) is among the world’s best documented GLOF regions. Yet hazard prioritisation frameworks still focus mainly on large lakes (>0.1 km²), while the numerous small (<0.01 km²) and medium (0.01–0.1 km²) lakes remain comparatively underassessed. In Huascarán National Park, 67% of the 882 inventoried lakes are small and 26% are medium-sized. In this study, we reconstruct the 28 April 2025 Vallunaraju cascade event in the Casca valley, where a rockfall impacted two small lakes and triggered an outburst flood reaching the Huaraz–Independencia conurbation 14 km downstream. Documented impacts included two fatalities and damage to five bridges, twenty-nine houses and water infrastructure. Although the modest initial lake-water release (~42 × 103 m3), progressive channel-bed entrainment increased the total moving mixture volume by ~6–7 times to 296 × 103 m3. 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%. We interpret Vallunaraju as a sediment-amplified cascade showing that small-lake outbursts can generate severe downstream consequences where triggers, abundant erodible sediment and exposure coincide, supporting integrated assessments that include small lakes, trigger susceptibility and propagation and exposure controls.