Lava lake surface characterization by thermal imaging: Erta 'Ale volcano (Ethiopia)

Active lava lakes represent the exposed, uppermost part of convecting magma systems and provide windows into the dynamics of magma transport and degassing. Erta 'Ale volcano located within the Danakil Depression in Ethiopia hosts one of the few permanent convecting lava lakes, probably active for a century or more. We report here on the main features of the lava lake surface based on observations from an infrared thermal camera made on 11 November 2006. Efficient magma circulation was reflected in the sustained transport of the surface, which was composed of pronounced incandescent cracks that separated wide plates of cooler crust. These crossed the lake from the upwelling to the downwelling margin with mean speeds ranging between 0.01 and 0.15 m s−1. Hot spots eventually opened in the middle of crust plates and/or along cracks. These produced mild explosive activity lasting commonly between ∼10 and ∼200 s. Apparent temperatures of cracks ranged between ∼700 and 1070°C, and of crust between ∼300 and 500°C. Radiant power output of the lake varied between ∼45 and 76 MW according to the superficial activity and continuous resurfacing of the lake. Time series analysis of the radiant power output data reveals cyclicity with a period of ∼10 min. The combination of visual and thermal observations with apparent mean temperatures and convection rates allows us to interpret these signals as the periodic release of hot overpressured gas bubbles at the lake surface.