Examination of the composition and spatial distribution of volcanic products in the Manda Hararo-Dabbahu rift segment, Afar (Ethiopia) using calibrated airborne hyperspectral Eagle and Hawk data

The concept of plate tectonics is widely accepted, and there is a reasonable consensus as to how it operates. However, the processes and controls involved in continental rifting and the generation of new oceanic crust are less well understood as such environments are commonly located in off-shore or remote settings. The current rifting episode and suite of eruptions in the Afar Depression (northern Ethiopia) offer a unique opportunity to study the interplay of magmatism and tectonism during continental break-up in an active setting. The multi-disciplinary NERC-funded Afar Rift Consortium was established to conduct an extensive study to enhance our understanding of geological activity at divergent plate boundaries. This paper outlines preliminary results from a large Hyperspectral airborne campaign over Afar, using the NERC Airborne Research and Survey Facility (ARSF) terrain survey and hyperspectral imaging capabilities. This was flown following an Alpha 5 proposal to the ARSF as part of the research conducted by the Afar Rift Consortium. An initial campaign in 2008 was severely affected by poor weather conditions however in November 2009 a second campaign successfully acquired 54 flight lines each of Eagle (VIS-NIR) and Hawk (SWIR) hyperspectral imagery, covering an area of approximately 1450 km2. The British Geological Survey (BGS), as a partner in the Afar Rift Consortium, has been tasked to geometrically and atmospherically correct 480Gb of raw hyperspectral data and to provide a seamless dataset as an input to the consortium. LiDAR data acquired during the campaign has been processed elsewhere and provided a suitable terrain model for geometric correction. Ground ASD field spectroscopy measurements acquired during the 2008 abandoned campaign enabled the removal of atmospheric artefacts. The resulting hyperspectral reflectance data have been analysed using hyperspectral image processing techniques to discriminate volcanic features, particularly to examine and map the compositional variations of young (< 1Ma) volcanic products in the centre of the rift segment. Initial investigations have focused on the Dabbahu volcano at the northern edge of the Manda-Hararo – Dabbahu rift. The area is part of an extensive igneous province and ranges in composition and eruptive style from effusive transitional basalts to explosive products of volcanism that are rhyolitic in composition. This research project has highlighted the successful contribution of Eagle and Hawk hyperspectral remote sensing to an igneous region where challenging terrain prevents extensive field mapping, and spectral analysis of broadband multispectral imagery (Landsat ETM+ and ASTER) has failed to adequately distinguish subtleties in compositional variation. However, it has also highlighted the challenges for data storage and processing capabilities associated with such a large hyperspectral campaign. Examples of the processed hyperspectral imagery will be shown in this paper