ERS SAR interferometry of an erupting volcano on a tropical island: Soufriere Hills volcano, Montserrat

SAR interferometry can, potentially, supply two types of useful information relevant to the 1995-99 eruption of Soufriere Hills Volcano, Montserrat: (i) the topography of the growing lava dome and its apron of pyroclastic flows, and (ii) the surface deformation of the volcano due to magma movement within. Phase information from ERS SAR data collected from July 1997 to November 1998 has been studied. The growing lava dome is too dynamic a surface to preserve topographic information, even with tandem data. Away from the dome the volcano does have some coherent surfaces on the lower flanks of the volcano covered by pyroclastic flow deposits. Some 35 day temporal baselines give reasonable interferograms, from which the authors have mapped changes in flank topography since the start of the eruption. Longer temporal baselines give progressively less information. To understand the differential interferometric signal requires the removal of the pyroclastic flow topography, and, perhaps, independent measures of the settling of the pyroclastic flow surfaces and the variability of the tropospheric water vapour.