In November 2007, the extrusion of a new lava dome evaporated Kelud volcanic lake in Java, Indonesia. Four months before a detailed echo sounding survey of the volcanic lake coupled to floating accumulation chamber measurements detected abnormally high carbon dioxide emissions. It constituted the earliest sign of the volcanic unrest; well before any other monitored parameter. CO2 flux is quantified using an empirical equation based on the volume of bubbles backscattered in the water column. Its comparison with the fluxes retrieved from the floating chamber method better constrain carbon dioxide dynamics in the volcanic lake. It reveals that 70% of the carbon dioxide enters the lake in a dissolved form, while the remaining 30% is supplied to the lake on a gaseous state. Almost three-quarter of the ascending bubbles dissolve in the water column leaving the majority of the 330 Tons day-1 of carbon dioxide diffusing at the air-water interface. Copyright 2012 by the American Geophysical Union. ; SCOPUS: re.j ; info:eu-repo/semantics/published ; 11 PP