THREE-DIMENSIONAL (3D) MODEL OF THE ERTA ALE VOLCANO IN THE AFAR DEPRESSION OF ETHIOPIA FROM REMOTE SENSING DATA INTEGRATION

The Quaternary Erta Ale shield volcano is located in the northern part of the Afar Depression in Ethiopia dominated by the Dankil Depression. It extends in a northwest-southeast direction for approximately 90 kilometers, and has a width of approximately 40 kilometers. While it is 613 meters high, Erta Ale volcano itself is found in a valley in the Afar Depression, situated 160 meters below sea level. The volcano was formed due to the stepping of the Red Sea spreading center onto land, and currently propagating in a southeast direction forming “embryonic spreading center” within the Afar depression. This is reflected in the seismic and volcanic activities, manifested in the presence of one of the few long-lived magma lakes on Earth. The vast extent of Erta Ale volcano, its remoteness, as well as its ground mapping logistical challenges, together with the lack of vegetation covers make it an ideal candidate for applying remote sensing technology to geological mapping. This work takes advantage of the availability of different types of remote sensing data to use an integrative approach to delineate geological features of the Erta Ale volcano and the surrounding Dankil Depression. It uses: (1) The 30 meters spatial resolution Landsat Thematic Mapper (TM) with six spectral bands in the Visible and Near Infrared (VNIR), and Shortwave Infrared (SWIR) region of the electromagnetic radiation for obtaining spectral information to map lithological variation. (2) The 25 meters spatial resolution RADARSAT C band (wavelength = 6 centimeter) to map surface roughness and morphological-defined structures. (3) The 90 meters spatial resolution Shuttle Radar Topography Mission (SRTM) to obtain topographic information of the terrain. Results of supervised classification were draped onto a Digital Elevation Model (DEM) obtained from SRTM data. This enabled differentiating between different pulses of volcanic eruptions, as well as mapping the various lithological units of the surrounding Dankil Depression. The result is a three-dimensional (3D) model of the Erta Ale volcano displaying the different rock units that can be viewed from different angles and at various scales. This work demonstrates the utility of remote sensing data integration for geological mapping in arid regions, especially remote and inaccessible terrains.