Volcanic plume thermal radiation: 1972 eruption of piton de la fournaise, Réunion Island

Using an infrared radiometer, the authors measured the infrared radiation emitted by the plume during the 1972 Piton de la Fournaise (Réunion Island) eruption in the 9.1- to 11.9-μm range.Eight histograms summarize twenty hours of continuous measurements and show a flux between 0.557 and 1.279 W/cm² with an average of 0.88 W/cm². The greatest number of events correspond to the flux emitted by lava fountains, while the high and rare flux values (4–6 W/cm²) correspond to detonations of chemical explosions, probably of H₂ and O₂.After calibration in the laboratory on a reference black body and in the field by correlation with field observations, such a technique can be used to follow changes of volcanic activity in remote and dangerous spots. Information on the number of explosions, their magnitude, and the presence and relative significance of hot magma can be transmitted continuously to a safe place.