Mass flux measurements at active lava lakes: Implications for magma recycling

Remotely sensed and field data can be used to estimate heat and mass fluxes at active lava lakes. Here we use a three thermal component pixel model wi th three bands of Landsat thematic mapper (TM) data to constrain the therma l structure of, and flux from, active lava lakes. Our approach considers th at a subpixel lake is surrounded by ground at ambient temperatures and that the surface of the lake is composed of crusted and/or molten material. We then use TM band 6 (10.42-12.42 mu m) with bands 3 (0.63-0.69 mu m) or 4 (0 .76-0.40 mu m) and 5 (1.55-1.75 mu m) or 7 (2.08-2.35 mu m), along with fie ld data (e.g., lava lake area), to place limits on the size and temperature of each thermal component. Previous attempts to achieve this have used two bands of TM data with a two-component thermal model. Using our model resul ts with further field data (e.g., petrological data) for lava lakes at Ereb us, Erta 'Ale, and Pu'u 'O'o, we calculate combined radiative and convectiv e fluxes of 11-20, 14-27 and 368-373 MW, respectively. These yield mass flu xes, of 30-76, 44-104 and 1553-2079 kg s(-1), respectively. We also identif y a hot volcanic feature at Nyiragongo during 1987 from which a combined ra diative and convective flux of 0.2-0.6 MW implies a mass flux of 1-2 kg s(- 1). We use our mass flux estimates to constrain circulation rates in each r eservoir-conduit-lake system and consider four models whereby circulation r esults in intrusion within or beneath the volcano (leading to endogenous or cryptic growth) and/or magma mixing in the reservoir (leading to recycling ). We suggest that the presence of lava lakes does not necessarily imply en dogenous or cryptic growth: lava lakes could be symptomatic of magma recycl ing in supraliquidus reservoirs.