Measuring the Rate of Lava Effusion by Insar

The rate at which lava emerges from a volcano is a fundamental property of the dynamics of the eruption. Intensive field measurements can capture this. However, for many, often cloud-covered, volcanoes with long-lived eruptions, spaceborne InSAR provides a potentially useful source of information. Repeated DEM creation at intervals allows the changing thickness of the lava flow field to be measured and incremental changes to calculate the volumetric lava flux rate. ERS data from (i) an andesitic lava dome eruption at Soufri re Hills, Montserrat , and (ii) a basaltic andesite lava flow-field at Arenal volcano, Costa Rica illustrate the method. There are two main limitations. Firstly, flowing or otherwise thermomechanically unstable surfaces that are active between interferogram pair acquisitions leads to decorrelation. This effect is particularly difficult on lava domes where the surface is extremely dynamic. Compound lava flow-fields are more tractable. Secondly, very slight motions on flows that have "stopped" can be confused with topography in repeat-pass interferograms. The InSAR-measured rate of lava effusion at Arenal fits well with rates calculated by other methods over the last 30 years. Radar systems best suited to this task should be L-band, have short orbit repeat intervals and moderate perpendicular baselines.