Activity: 1800s-1966

The first scientific description of Oldoinyo Lengai was by G.A. Fischer in 1883. He observed “smoke” rising from the summit and recorded reports by local people of rumbling noises within the mountain (Fischer 1885, quoted in Dawson et al. 1995). The first scientist to climb to the summit crater was F. Jaeger in 1904. C. Uhlig and F. Muller climbed the volcano on 4 August 1910 and observed that “the northern crater had only a horse-shoe-shaped southern rim immediately below the summit, and lacked a crater rim to the north, west and east. The crater was more like a platform on which there was a central cone from which gas was being emitted”. Lava flows and pinnacles formed on this platform between 1904 – 1910 and again between 1913 – 1915.

A major explosive eruption took place from January to about June 1917. Ash was deposited as much as 25 – 30 miles away, and killed the formerly luxuriant vegetation on the lower slopes of the mountain. The flat lava platform was replaced by a deep summit crater. Another eruption may have occurred for several months in 1926.

The first eruption of which there is a fairly complete record took place between July and December 1940. J. Richard’s account of this eruption identifies three major phases (1) a preliminary stage of small explosions that discharged old material from the vent, (2) a phase during which great quantities of gas were discharged, preceded by violent explosions that ejected blocks and bombs, (3) a phase during which mainly ash was ejected, but not to such great heights as during phase 2 (Richard 1942). At the close of this eruption there was a deep funnel-like hole in the summit crater, the slopes of the volcano were blanketed with white ash, and ash had fallen as far west as Loliondo, about 100 kilometres away.

Minor eruptions of lava were observed in 1954, 1955 and 1958; a small eruption of ash may have occurred in early 1955.

Similar minor lava eruptions were recorded from several dates in the early 1960s; see the photographs below. The photograph to the left shows activity taking place from a small cone on the crater floor. The photograph to the right is a closeup of the same eruption. Both these photos were taken by Dick Moss in June 1961. Note the steep walls of the crater in the left hand photograph and the eruptive activity in the right hand photograph. In the foreground is an active pahoehoe flow and in the background lava bubbles are bursting in an open vent. This activity is identical to the activity that has been observed frequently since 1983.

In early August 1966 the crater had steep rugged walls, as shown in the photograph to the right, taken by Gordon Davies; similar small cones and lava flows were forming on its floor.

In mid-August 1966 this form of activity gave way to a violent explosive eruption.

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