Djibouti borders Eritrea to the north, Ethiopia to the West and Somalia to the South. Its Eastern coastline is strategically placed on the Bab el-Menab Strait, at the top of the Gulf of Aden and at the mouth of the Red Sea. The Djiboutian port serves as the gateway to the Suez Canal, one of the world’s busiest shipping routes. The port is the lifeblood of the economy, providing the biggest source of income in this country. The estimated population is circa 923,000, the majority of whom live around the capital also called Djibouti. The land area is 23,200 km2.
Figure 3. Location map of Djibouti
Djibouti is covered by a large lava field interspersed with volcanos and craters. The country is at the centre of the Afar Triangle, a wide area (~200 000 km²) acting as a triple junction where the three rifts of Red Sea, Ethiopian and Gulf of Aden are converging. The connections of those rifts are asymmetrical and create a complex diffuse deformation creating the Afar depression, a unique situation in the world with continental-rift merging with oceanic-rift.
Figure 4. Djibouti geology overview
Djibouti’s topography is closely linked with the recent geologic history. The country is shaped by the long fracture lines oriented mainly NW-SE, cutting the country into long plateau and deep depressions including the famous Assal lake at -155m below sea level. The Assal rift in geographic centre of the country divide the country into two main zones on each side. In the north part of the gulf of Tadjourah lies mountain ranges and plateau made of basalts and rhyolites (mount Eguer Aleïta: 1 799m). The south western part of the gulf and Assal rift is made of a series of asymmetrical grabens and horsts with rift within rift structures. The deepest depression is host of the Assal lake the lowest point in Africa at -155m below sea level, but also the location of the youngest volcanic eruption, Ardoukôba in 1978. The Assal lake is surrounded by a salt plain deposited by continuous evaporation of the lake, while being refilled by the sea through cracks on the rift axis. At the western border with Ethiopia lie the Abhé Bad lake within another depression. It is a unique sight with carbonate chimney up to tens of meters high, with fumaroles and hot springs from volcanic activity. Most of the other depressions are closed basins filled with sediments bordered by high ridges (above 1000m high), including Gaggadé and Hanlé.
The Assal Rift
The rift of Assal (12-15 km wide) with its NW-SE trend is an active rift, with the latest eruption dating back to 1978 (volcano Ardoukoba). The rift is the continental continuation of the oceanic spreading axis of the Gulf of Aden, going through the Gulf of Ghoubbet with a NE-SW direction and into the lake of Assal with a NW-SE direction. It is opening at a rate of few centimetres per year, while the floor is sinking and the shoulders are rising. Fault planes are steep (>80° dip) with mostly normal dip-slip movement (200m throw), they may also locally become reverse. The rift is covered by numerous open fissures and small faults, reaching width of several meters and length of some kilometres. These fissures are mostly parallel to the main extension, but others show a E-W orientation consistent with a sinistral strike-slip parallel to the rift. Antithetic faults generate small asymmetrical grabens and horsts (rift within rift), this asymmetry is furthermore marked by the offset between the zone of strongest tectonic activity (NE) and that of most intense volcanism and fumarole activity (SW). Thus, suggesting a NE migration of the spreading axis. The asymmetry of the rift is also seen in the rock formations, the southwest margins are in the Stratoïd Series, while the northeast margins are in the Dalha Series overlying the Mabla rhyolites of the Danakil Block. Many springs and fumaroles are located along the shore of Assal lake, which coincide with the rift axis.
Figure 5. Salt plain of the Assal lake
Figure 6. Abhé Bad lake with its massive carbonate’s chimney
Assaleyta exploration permit
Assaleyta prospect is located on the south shoulder of the Assal rift. The Assaleyta exploration permit covers an area of 70.9 km². The prospect lies 1km from the road RN10, 110km from Djibouti city and 10km from the Assal lake.
Figure 7. Assaleyta exploration permit (Landsat background)