With only a few visitors per month, news from the “mountain of the Maasai gods” is rare and often difficult to use to understand the evolution of volcanic activity over time. But two recent expeditions by the 80 Jours Voyages agency one year apart show a gradual and moderate evolution of the active vents over time, as well as an undeniable filling of the small summit crater… This will also interest you[EN VIDÉO] 8 things to know about volcanoes Objects of fascination and terror, volcanoes are among the most irreducible forces… as evidenced by the thermal signals frequently spotted inside the summit crater on satellite images of this sector. But the temperature of this very special lava – a carbonatite – being around 500°C, the thermal signals are quite weak compared to more traditional lava eruptions, which prevents accurate assessment and monitoring of the activity. It is then necessary to rely on direct observations which are quite rare, because the volcanovolcano is in a fairly desertdesert place and its ascent is dissuasive, even if the spectacle promised up there is obviously worth the detour… A crater which gradually fills up he paroxysmal eruption of 2007-2008 formed a crater about 300 meters in diameter, with a steep central part whose floor was estimated to be 120 meters deep. After this event, the classic activity resumed quickly, rather on the edges of these steep walls, and had already raised the crater floor by about twenty meters. Today, it is located around 2,800 meters above sea level, about 70 meters below the lip of the crater and seems to have risen a little more than five meters in a year… If the activity continues in this way, it it will therefore probably be necessary to wait at least two decades for the filling of the crater to be complete and for it to overflow again, as between 1998 and 2007! Unlike last year’s expedition, no recent large lava flows could be noticed. The active vents were still in a central position, some in the same position as the year before, but they are difficult to recognize as these volcanic conescones are fragile and therefore with a very changing morphologymorphology… Thanks to Sylvain Chermette, manager of the agency 80 Jours Voyages which allows me to use these photos free of charge, thus illustrating this article nicely. There are still places available for his stay on Lengaï from June 7 to 17, 2024. Discovering the most unusual volcano on the planet With its vertiginous sides and volcanic silhouette, it stands in the middle of the Tanzanian savannah, not far from the Lake Natron. According to the Maasai people, a semi-nomadic tribe living in this sector of Africa, the volcano is inhabited by the creator god Engai, who gave it its name. Superb landscape, mystical place, the mountain of the Maasai gods is also a volcanological curiosity! Because this volcano is the only one in the world to emit carbonatites, lavas of black color when they are in fusionfusion and which become white as they cool… Article by Ludovic LeducLudovic Leduc, published on April 13, 2023 This volcano is located in the beautiful middle of the East African rift which crosses Africa for at least 5,000 kilometres, from Afar to Mozambique. This rift is the consequence of an extensive process which, in time, could split the African continent in two. This allows the partial melting of the coatcoat at this level, but with a very low rate, which produces magmas rich in alkalines (sodiumsodium and potassiumpotassium in particular). The ascent of this magma in the earth’s crustearth’s crust towards the volcano would then be associated with a process of separationseparation of two magmatic liquidliquids, magmas that can be differentiated by their siliconsilicon content. The first is silicate, like the vast majority of terrestrial magmas, and nepheline in nature. It constitutes a deep reservoir of the volcano. The mysterious origin of the astonishing carbonated lavas of Lengaï unveiled But, from this magma, a second liquid is extracted because of its immiscibility with the first and, by contrastcontrast of density, rises in the volcanic edifice to form a superficial reservoir. This magma is very special, because it contains less than 20% silicon (against more than 40% for all other magmas on EarthEarth) and is very rich in calciumcalcium, sodium and potassium: it is carbonatitic in nature. Eruptions of two kinds This superficial reservoir feeds the almost permanent activity of this volcano, a unique activity on our Planet! Indeed, Ol Doinyo Lengaï is the only terrestrial volcano that emits this type of lava! However, these lavas are very surprising: they are exceptionally fluid, black to dark brown in color when they are in fusion and at around 500°C only — compared to 800 to 1,200°C for “classic” magmas. ! In addition, they react very quickly in the atmosphere and, in a few hours, the mineral carbonates alter and whiten… If these carbonatites make the singularity of this volcano, they nevertheless only make up about 5% of the volumevolume of the volcano, the rest corresponding to the nepheline magma! The latter is associated with violent eruptions which, in general, recreate a crater at the top of the volcano. Thus before 2007, the summit crater of the volcano was filled, completely filled by the carbonatites emitted during the previous four decades, to such an extent that the crater overflowed. So much so that the curious could venture as close as possible to these astonishing lavas! But a violent eruption occurred from September 2007, with a paroxysm in February 2007 during which an ash plume 15 kilometers high was formed! A crater 300 to 350 meters in diameter was shaped during this eruption, instead of the platform before… Then, as after the violent eruptions of 1917, 1940-1941 and 1966-1967, the carbonatitic activity has resumed, and is beginning to fill this deep crater… A black and white crater now observable climb to the top of the volcano. We can thus see that the floor of the crater is gradually rising, so that the activity is now observable in good conditions… This is how in June 2022, Sylvain Chermette and his clients observed five to seven active vents at the bottom of the crater, aligned in a west-northwest/east-southeast direction. The activity on each of them was variable. Here, projections reached a few meters high, building relatively erect cones several meters high. There, flows poured out at the bottom of the crater. In the center of it, the base of an ancient imposing and collapsed cone sheltered small bubbling lakes… A varied spectacle according to the vents therefore, according to the day and the night, but also during the three days that they remained at the top of the volcano. Sylvain Chermette is going back there next June: will the volcano have evolved? Thanks to Sylvain Chermette, manager of the 80 Jours Voyages agency, who allows me to use these photos free of charge, thus illustrating this article nicely. There are still places available for his stay on the Lengaï next June. The activity of Lengaï in video. © Sylvain Chermette, 80 Days Travel