Remarkable geochemical changes and degassing at Voui crater lake, Ambae volcano, Vanuatu

• Published in: Journal of volcanology and geothermal research 2009-12, Vol.188 (4), p.347-357
• Main Authors: Bani, Philipson, Oppenheimer, Clive, Varekamp, Johan C., Quinou, Thomas, Lardy, Michel, Carn, Simon
• Format: Article
• Language: English
• Subjects: Ambae volcano; crater lake colour change; Crystalline rocks; Earth Sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Geochemistry; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Lake Voui; Sciences of the Universe; SO 2 emissions; Volcanology
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/j.jvolgeores.2009.09.018

Ambae (also known as Aoba), is a 38 × 16 km 2 lozenge-shaped island volcano with a coastal population of around 10 000. At the summit of the volcano is lake Voui — one of the largest active crater lakes worldwide, with 40 × 10 6 m 3 of acidic water perched 1400 m a.s.l. After more than 300 years of dormancy, Ambae volcano reawakened with phreatic eruptions through Voui in 1995, and culminating in a series of surtseyan eruptions in 2005, followed by a rapid and spectacular colour change of the lake from light blue to red in 2006. Integrating lake water chemistry with new measurements of SO 2 emissions from the volcano during the 2005–2006 eruptive period helps to explain the unusual and spectacular volcanic activity of Ambae — initially, a degassed magma approached the lake bed and triggered the surtseyan eruption. Depressurization of the conduit facilitated ascent of volatile-rich magma from the deeper plumbing system. The construction of a cone during eruption and the high degassing destabilised the equilibrium of lake stratification leading to a limnic event and subsequently the spectacular colour change.