Formation of new beaches from lahar deposits, Ambae volcano, Vanuatu

Lahar deposits resulting from the eruption of Ambae (Vanuatu) in 2017–2018 were transformed into black sand beaches at the discharge points of water flow paths. This occurrence represents a novel and unreported phenomenon for Ambae. This study proposes that the combination of steep slopes generally 20–25% with relatively short flow paths (5–10 km) and substantial ash accumulation at the summit facilitated the rapid transfer of material from the volcanic summit to the coastal zone, providing the energy necessary for the gradual seaward extension of the coastline and the formation of beaches. The occurrence of this phenomenon is limited to specific areas, contingent upon the distribution of ash deposits on the summit. The western section of the crater's summit has predominantly accumulated ash, partially due to the consistent presence of trade winds. This region coincides with the origins of the flow paths supplying the lahar zone. Since 2018, the newly formed beaches persist, offering promising prospects for the island's development, including the identification of freshwater sources. The study also delves into the most destructive event of the eruption and proposes that a combination of the lahar and landslide events precipitated the destruction of the village of Waluembue. Paradoxically, the lahar's arrival preceded the landslide, providing a warning call to the inhabitants and giving them crucial time to evacuate before the catastrophic impact.

Christy Haruel, Philipson Bani, Dan Tari, François Nauret, Estelle F. Rose-Koga. Formation of new beaches from lahar deposits, Ambae volcano, Vanuatu. Bulletin of Volcanology, 2024, 86 (8), 73 [12 p.]. ⟨10.1007/s00445-024-01755-3⟩. ⟨insu-04676494⟩
docType_s : ART
journalTitle_s : Bulletin of Volcanology
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