Ran across this one via Smithsonian GVP. It is a smallish volcanic eruption NW of the Ethiopia – Djibouti border. Manda – Inakir was the site of a 1928 – 1929 basaltic eruption that created a cinder cone and lava flow near the village of Korili and the Andabba Plain.
The region is part of an active seafloor rifting event that is part of the Afar Depression. Recent volcanic eruptions associated with the rifting event include Ardoukoba 1978 to the SE of Manda – Inakir, a major rifting event at Dabahu – Manda Hararo 2005 – 2010 to the NW, an eruption from Erta Ale in 2008 farther to the NW, and an eruption from Nabro to the NNE in 2011. Granyia did an excellent post on Ardoukoba November 2016.
We will use the Manda – Inakir as a starting point for the larger discussion of recent volcanism in the region.
The region is perpendicular to the Ethiopian – Djibouti border in the Ethiopian highlands. The location of the most recent eruption in 1928 – 1929 is a full 600 m above sea level in Djibouti near the SE end of the rifts. Volcanic activity here is concentrated along two parallel rifts, Manda and Inakir. The rifts are generally NW – SE with the southern end in Djibouti. There is a volcanic edifice located right at the triple junction between the three national borders, Ethiopia, Djibouti and Eritrea.
Climate is generally hot and dry with cooler desert nights. Trees and local forests tend to be located where local water pools.
Surrounding villages are Bure to the north, Dorra to the SE and Assa Gaila to the ESE.
The Smithsonian GVP lists only 16,000 within 30 km of the volcanoes and 224,000 within 100 km.
The region is economically poor, with little infrastructure. Though there is a proposed geothermal project on the Djibouti side of the border based on the presence of magma relatively close to the surface. A 2012 paper by Haga, et al described field studies necessary to exploit the Manda – Inakir rift system for geothermal energy. Surveys of the region discovered active fumaroles, hot springs on the sedimentary plains, and gas emissions from several sites surrounding the fissure system. Drilling for local water wells has discovered what is described as anomalous hot water occurrences, with occasional temperatures above 80 C. There is an extensive hydrothermal system associated with the rifting volcanism. Initial research into geothermal potential of the region suggests it can support a number of micro-geothermal plants in the 10 – 100 kW range. Well depths would be in the 1 – 2 km range.
Since this is my first excursion into the Afar Triangle, a short discussion of the region is in order. In short, the region is a tectonic mess, as a triple junction of rifts propagates W to SW into Africa. This propagation has been driven by what is called the Ethiopian Plume Head, a hotspot that arrived around 30 Ma. The plume head arrival created the most recent Large Igneous Province eruption sequence in the Afar with basalt eruptions peaking some 30 Ma.
The Afar is defined by the Ethiopian plateau to the west, Somali plateau to the SE and Danakil Highlands to the NE. The Ethiopian trap basalts were erupted 31 – 29 Ma. Total coverage of these basalts was 210,000 km2 on the Africa side of the combined rifts. Activity in Yemen covered at least 80,000 km2. Total volume of these traps is estimated at 1.2 million km3. These eruptions coincided with regional uplift of the Ethiopian plateau. The Ethiopian plateau has been lifted at least 2 km by the underlying mantle plume.
Overall tectonic movement has been movement of the Arabian Plate away from Africa, opening the Red Sea. The Aden Ridge propagates in from the East and the Eastern Africa Rift propagates in from the SW. The triple junction for all these tectonics is the Afar, which has the Ethiopian Plume head underneath it, providing copious amounts of eruptible magma. The overall Ethiopian plateau is split to the east by the Afar and to the SW by the East African Rift.
The northern portion of this active region is defined by the propagation of rifting under the Red Sea. The SE end of this rift moved inland and continues to rift in roughly 60 km long segments. These segments are typically parallel separated by a couple kilometers. Erta Ale, Tat Ale, Alayta and Dabbahu – Manda Hararo activity is all related to SE propagation of this rifting event.
Recent activity in the Afar are located along axial grabens along the rifting segments, and include fissure eruptions, silicic central volcanoes and basaltic shield volcanoes. This volcanic activity is similar to that along mid-oceanic ridge segments. There are similarities to the relationship between fissure swarms and central volcanoes also seen in Iceland.
In addition to the Large Igneous Province event 31 – 29 Ma, there have been multiple volcanic episodes in the Afar. The most prolific of these were the Mabla rhyolites, 14 – 10 Ma, the Dahla basalts, 8 – 6 Ma, and the Afar Stratoid Series, 4 – 1 Ma. In some ways, volcanic activity has been nearly continuous for the last 4 Ma in the Afar.
Central volcanic centers produce basalts while marginal volcanic centers produce trachyites, rhyolites and ignimbrites. The Stratoid Series is a pile of 1 – 6 thick pahoehoe basalt flows up to 1,500 m thick on the floor of the Afar Depression.
Dabbahu – Manda Hararo Rifting Event
The Dabbahu – Manda Hararo activity 2005 – 2010 is the most recent volcanic activity associated with rifting propagation. The Manda – Inakir activity is at the SW end of this rifting segment.
The 2005 activity began in September with a large dyke emplacement. There was a small rhyolite eruption from a fissure at the northern tip of the dike. This rifting event opened a series of fissures and reactivated faults along a 60 km segment of the rift. Dike volume was 2.5 km3 with the source being near the center of the rift. The dike was detected via seismicity and surface deformation.
Crust thickness of this part of the Afar varies from around 16 km to the north and 45 km beneath the Ethiopian plateau.
Since this began in 2005, there have been 13 basaltic dikes emplaced. There have been three small volume basaltic eruptions from the southern and central parts of the axial graben in 2007, 2009 and 2010. These fissure eruptions produced rubbly pahoehoe flows up to 2 m thick.
Manda – Inakir Rift Volcanism
The Mousa Ali stratovolcano sits on the tri-point intersection of the Ethiopia, Djibouti and Eritrea borders. It is 2,021 m high, topped with a caldera, and rhyolite lava domes and flows. Its most recent eruption was perhaps 500,000 years ago. The Wiki describes its vegetation as lush with flowering shrubs and plants. This vegetation supports abundant wildlife. It is perhaps 10 km to the NE of the Manda – Inakir volcanic rifts.
The Manda – Inakir range has two rift zones. The older Inakir rift has volcanic rocks overlying a NW – SE dome 12 x 25 km cut by a 2 – 3 km wide rift zone. The more recent Manda rift has roughly the same orientation, parallel with the Inakir rift. It projects into Ethiopia with only the southern end in Djibouti. That end is 2 km wide and fractured.
The older Inakir rift had volcanic rocks overlying an 12 x 25 km dome of basement rocks. It is cut by a rift 2 – 3 km wide with 250 m of subsidence in the rift. There are basaltic cinder cones along the faults along the rift that erupted lava flows down the flanks of the dome, making the entire structure appear to be a large shield volcano. Activity along the Inakir rift dates 350 – 190,000 years.
The newer active Manda rift mostly lies in Ethiopia, with only its southern end in Djibouti. The densely fractured rift zone is 2 km wide. The northern rift has been volcanicly active during historic times. Basaltic volcanic activity built cinder cones along the fault lines defining the rift. The most recent eruption was 1928 – 1929 near Korili in Djibouti built the Kammourta cinder cone and lava flow. The complex is uplifted to 600 m above sea level. Activity along the Manda rift dates 140 – less than 25,000 years, with the newest eruptions generally in the western portion of the rift in Ethiopia. Interestingly, the most recent eruption was in the SE portion of the rift near the Andabba Plain.
The Smithsonian GVP lists five volcanic features associated with Manda – Inakir. Volcanic cones include Andabi Gabalti and Kammourta, which was the most recently active volcanic feature. There is the Dirdo Koma crater and the Inakir and Manda fissure vents.
The 1928 – 1929 eruption started with strong earthquakes. Residents in Korili village 10 km from the new volcano saw dust in the sky and hears explosions. The newly constructed Kammourta volcano ended up being 400 tall and 400 m wide with two lobes of a’a lava flowing SE toward the neighboring Andabba Plain.
Earthquakes associated with the eruption lasted a month and opened up fractures on the SW side of the Andabba Plain that modified the drainage patterns into the plain by as much as a meter. It also rearranged growing patterns of a small forest at the foot of the Inakir.
Tectonics in the region have been driven by the actions of what is called the Ethiopian Plume Head that reached the bottom of the plate boundaries some 30 Ma. Initial rifting was along the East African and Red Sea rifts. The Gulf of Aden rift began its propagation from the Indian Ocean toward the hotspot (plume head) area and arrived in the vicinity some 20 Ma. At the same time, the Red Sea rift propagated southwards, also toward the hotspot (plume head) area.
The Afar depression started to stretch and open. Two microplates, the Danakil and Ali Sabieth blocks were isolated around 10 Ma and the depression started to open.
In the last 4 Ma, rotation started in central Afar. By 1 Ma, the Aden rift was on the western edge of the Danakil block and has been propagating northward. The established Manda – Harro rift that marked the southern end of the Red Sea ridge system (rift / spreading center) propagated southwards along the western edge of the Afar depression. At least 5 small blocks rotated during the last 1 My. Their western ends broke loose, and the eastern boundary was anchored to the Ali Sabieth microplate.
Early opening of the Gulf of Aden has been episodic with varying speeds. It was initially rapid and then slowed and stalled as the Aden rift reached the plume area 10 Ma and stalled some 10 – 4 Ma. Spreading was transferred into the Afar and propagated northward. This created a lacerated structure of Afar volcanics with rotated volcanics, stripes and blocks generated by rift and transfer zone propagation as the zone propagated. This will eventually lead to continental breakup.
Manda – Inakir, Manda – Hararo, and the greater Afar region will continue to rift as the continental rifting event progresses. There will be periodic outbreaks of basaltic volcanism, uplift, subsidence, as the seafloor spreading continues. At some later date, the sea will invade the newly rifted area, not unlike what it has done in the Gulf of California. Expect volcanic, earthquake and tectonic activity in the region to continue.