Eruptive history of Dubbi volcano, northeast Afar (Eritrea), revealed by optical and SAR image interpretation
A study of the remote Dubbi volcano, located in the northeastern part of the Afar triangle, Eritrea, was carried out using JERS-1 Synthetic Aperture Radar (SAR) and Landsat Thematic Mapper (TM) imagery. It investigated the last known eruption of Dubbi volcano in 1861, the only volcano in Afar for which historical reports indicate a major explosive eruption. Various image processing techniques were tested and compared in order to map different volcanic units, including effusive and explosive products. Principal component analysis and optical-SAR fusion were found to be useful to determine the extent of the 1861 pumice deposits surrounding the volcano. SAR imagery revealed old lava flows buried below tephra deposits, emphasizing the ground penetrating property of the L-band (HH polarization). The interpretation obtained from satellite imagery was cross-checked with sparse historical testimonies and available ground-truth data. Two scenarios are proposed for the 1861 eruptive sequences in order to estimate the volumes of lava flows erupted and the timing of explosive and effusive activity. Identified as a bimodal basaltic-trachytic eruption, with a minimum volume of 1.2 km3 of hawaiite lava and a minimum area of 70 km2 of trachytic pumice, it represents the largest known historic eruption in the Afar triangle. This paper raises the issue of the potential volcanic hazards posed by Dubbi, which concern both the local population and the maritime traffic using the strategic route of the Red Sea.