GRSG Conference 2020 Presentation

Title: Remote Sensing Methods applied for Geothermal Exploration in North Ghoubbet, Djibouti

Author: Alina Ermertz

The exploration of geothermal sites includes complex studies of geological, geochemical and geophysical conditions and is a very time- and cost-consuming process.

The application of remote sensing data is a major advantage for such reconnaissance studies, as wide-ranging information can be gathered prior to detailed studies of specific sites. Especially in areas where accessibility is a limiting factor, remote sensing studies save time and effort.

In terms of the BGR Project “Geothermal Energy in East Africa”, the exploration of geothermal sites in Djibouti is supported in several fields of expertise, including geochemistry, geophysics and remote sensing.

Remote sensing methods are applied to define areas of enhanced geothermal potential in the study area “North Ghoubbet”. The geological setting is characterized by the location of Djibouti within the Afar Triple Junction, where the two spreading ridges of the Red Sea and the Gulf of Aden meet the East African Rift System. This setting results in major tectonic and volcanic activity along the active Asal-Ghoubbet Rift system bordering the study area to its southwest.

Freely available multispectral remote sensing data of the Sentinel-2 mission as well as digital elevation models derived by the SRTM mission are used for detailed lineament mapping.

The knowledge of the structural framework of an area is very important for the assessment of geothermal potential, as a high density of lineaments indicates enhanced permeability for hydrothermal fluids and therefore enhanced geothermal potential.

Lineaments primarily strike parallel to the Asal-Ghoubbet Rift system, being oriented NW-SE while conjugated structures appear in a NE-SW direction. Three different areas, where a high density of lineaments coincides with fumarolic activity, were defined for further exploration.

Field investigations show that fumarolic activity occurs in alteration zones of several meters of extension, characterized by intense alteration of the basaltic bedrock. Alteration minerals predominantly are clay minerals and iron-bearing minerals that are mapped including Worldview-3 data in the analysis.

The combination of both, lineament mapping and alteration mineral mapping, contributes to a basic understanding of the geothermal reservoir in North Ghoubbet.