Crater lakes reveal volcanic heat and volatile fluxes

Aqueous lakes situated at the top of active but quiescent volcanoes serve as gas condensers and calorimeters that provide long-term integrated release rates of volatiles and heat during passive degassing of subsurface magma. Some crater lakes contain the most acid natural water on Earth (pH <0). Analysis of hydrogeology of the acid lake at Volcan Poas, Costa Rica, reveals volatile release rates into the hydrosphere of 0.78 Gg/yr fluorine, 15 Gg/yr chlorine, and 13 Gg/yr sulfur (1 Gg = 10⁹ g) and a power output of 200 MW during passive degassing in 1988-1989. An equivalent flux of sulfur may be precipitating as chemical sediments in the crater lake. After magma intrusion or hydrofracturing events in the subsurface, these fluxes were observed to double (F, Cl) or even increase tenfold (S) for short periods of time. Data from Grimsvotn volcano, Iceland, are also presented. Power output for each volcano can also be used to calculate rate of magma cooling in the subsurface. -from Authors