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

摘要

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 ma.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 leadinf to a limnic event and subsequently the spectacular colour change.