Erta Ale

The Erta Ale is a Volcan shield of Ethiopia located in the north of the Vallée of the great rift, more precisely in the depression Danakil. Erta Ale means smoking mountain in afar.

Presentation

Erta Ale, although not very high (613 meters of altitude), is very étendu : thirty kilometers diameter. It belongs to a volcanic system including/understanding of North in the South the Gada Ale, the Aluminum-Paved Spun, the Borale Ale, Erta Ale, the Hayli Gub and the Ale Bagu which is stretched on 95 kilometers length and 42 kilometers broad. It has a surface of 3800 square meters It is also in the south of the Volcan Dallol.

Erta Ale has at its top a Caldeira of 1 600 meters length on 700 meters of broad directed North-South. In will caldeira are two crater S in the shape of round shafts and with the vertical walls. According to the volcanic activity, lakes of lava are placed in these craters and disappear or overflow temporarily.

Located in a desert and not very easy area of access, Erta Ale is studied volcanologists only since the end of the Années 1960 and the beginning of the Années 1970 but it was observed by Europeans for the first time in 1841 and was climbed in 1873.

The Afars do not approach it, considering that it is the place of life of malfaisants spirits assembling horses.

Eruptive history

In 1968, the first forwarding free - Italian volcanologists arrived at the top of Erta Ale. Haroun Tazieff and Giorgio Marinelli observes two lakes of lave then;: in the northern crater a lake one hundred meters in diameter and very credit and in the central crater a lake 65 meters in diameter and less credit, both being located at a 165 meters depth and being probably active since at least 1906. The level of the lakes did not cease a remonter : in 1971, they were only with one ten meters of the edge of the craters and had about the same diameter and in 1972 they overflowed by drowning the floor of the Caldeira under lava flows. The situation will last until in 1974.

No other observation was carried out until November 1992 except some air overflights and of the satellite observations. A crumbling of the walls of the northern crater had hidden the lake of lava under a mass of remains and the level of the central lake, whose dimensions were from 40 to 70 meters, was gone down again to hundred meters.

In 2001, the war with the Érythrée finishes and of the teams of scientists can make measurements. The lake measures 80 by 100 meters then, is placed with a 80 meters depth and regularly emits fountains of lava from five to ten meters in height. Since this date, the volcano is regularly visited. The observation of the lake of lava shows frequent changes of levels and activity.

The lakes of lava show intense a activité : it is formed a crust of cooled lava but this one is bored by fountains of lava maintained by regular volcanic gas increase. Moreover, currents of convection exist in the lava of the lake, which animates the crust of movements. One can then to some extent observe zones of accretion and miniature Subduction such as in the dorsal and the pits of subduction.

Today, the two lakes of lava it are cooled, and are wrapped of a thin layer of basalt. In the largest crater, only four fumerollic chimneys (Hornito S) are still present, revealing the interior of the magma in fusion still in flow. But the lake of lava can recombler constantly.

Geology

The lava emitted by Erta Ale basaltic, is slightly gasified and its higher measured temperature rose with 1 217°C. These data indicate that the magma is of the same type as that emitted on the level of the oceanic dorsals.

The heat flow measured is of 30.10 ³ watts/m ².

Indeed, the Danakil depression where the volcano is located constitutes in fact a branch of the continental rift which course Eastern Africa of North to the South and which will in the long term give a new ocean or a new standard sea in the same way than the Red Sea.

See too

Valley of the great rift
Geography of Ethiopia
Volcano Dallol
Afar
Danakil

External bonds

Erta Ale on the site of Total the volcanism programm
Futura sciences - File on Erta Ale

Sources

Site of the Company Geneva Volcanology on Erta Ale

Reference

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