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 th e Afar triangle, Eritrea, was carried out using JERS-1 Synthetic Aperture R adar (SAR) and Landsat Thematic Mapper (TM) imagery. It investigated the la st known eruption of Dubbi volcano in 1861, the only volcano in Afar for wh ich historical reports indicate a major explosive eruption. Various image p rocessing techniques were tested and compared in order to map different vol canic units, including effusive and explosive products. Principal component analysis and optical-SAR fusion were found to be useful to determine the e xtent of the 1861 pumice deposits surrounding the volcano. SAR imagery reve aled old lava flows buried below tephra deposits, emphasizing the ground pe netrating property of the L-band (HH polarization). The interpretation obta ined from satellite imagery was cross-checked with sparse historical testim onies and available ground-truth data. Two scenarios are proposed for the 1 861 eruptive sequences in order to estimate the volumes of lava flows erupt ed and the timing of explosive and effusive activity. Identified as a bimod al basaltic-trachytic eruption, with a minimum volume of 1.2 km(3) of hawai ite lava and a minimum area of 70 km(2) 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 rout e of the Red Sea.