The 2009-2010 eruption of Gaua volcano (Vanuatu archipelago): Eruptive dynamics and unsuspected strong halogens source

During this eruption the quiescent and voluminous Lake Letas was slightly affected by the eruption. Nevertheless the hydrothermal discharge point into the lake, situated on the southeastern part of Mt. Garet appeared to be relatively active. At this particular location rock forming elements, leached out from volcanic rock by acid fluids released by the new intrusion of magma, were discharged along with anions into Lake Letas. This release has triggered localized chemistry changes in the lake. We speculate that this discharge has also disturbed the bottom water in a limited perimeter, remobilizing reduced Fe to the surface and subsequently triggering the change in the water color by Fe oxidation.