We do not have a detailed eyewitness account of the events in May-June 1993, but from interviews with people who were near the volcano at the time, and photographs by Martin Kuper of Zurich it is possible to put together a reasonable picture of what happened. Minor activity occurred through April 1993, and there are reports of a loud explosion near the summit on about 22 May. During an ascent on 8 June 1993 Burra Gadiye observed that T20, a cone in the centre of the crater floor, had grown considerably. Also a large amount of steam was escaping from a crack on the west slope of the volcano, a few hundred metres below the west rim. Burra reported feeling an earthquake on 14 June and dark, dense plumes from the crater could be seen from Ngare Sero, the village about 10 kilometres north of Oldoinyo Lengai. Maasai herdsmen moved their livestock out of the area. On 15 June Burra climbed the west slope but was unable to reach the rim, being stopped by flowing lava in the approximate vicinity of the steam on 8 July. Dark ash was being erupted from within the summit crater on 15 June, and again on 18, 21 and 25 June. When a party from St. Lawrence University climbed the west slope on 27 June, we observed no ash clouds from the crater, though there was a strong smell of sulfur detectable from far below the crater rim. There was a light dusting (maximum about 2 mm thick) of fine gray ash on the outer slopes, and a lot of dead vegetation on the upper slopes. Steep rock slabs a few hundred metres below the rim were covered with several centimetres of loose ash, making climbing very difficult. It was not possible to proceed up the path to the rim, as it was blocked by slabs of lava, by now cold and solid.
Martin Kuper was flying over the crater on 15 June and his photographs show what was happening there.
The photograph to the left above, taken looking to the southwest across the southern part of the crater, shows a large area of very fresh lava filling in the southern part of the crater floor, with lava fountaining taking place from the centre of this lava lake. As Martin Kuper described "It was marvellous, moving, bubbling and made high fountains". The photograph to the right, taken from the west, shows the lava flow on the outer west wall of the cone, black in colour against the white and grey slopes of the cone. This lava was apparently emitted from a source just above two erosional buttes and the photo shows it ponded up above these buttes and forming a thin line between them. This line was the old path up the west slope so it is not surprising that Burra Gadiye and the St. Lawrence University party could not climb to the west rim in late June!
Later in 1993 Eric Christin took the photograph on the left, looking up the rugged lava flow between the two erosional buttes. By the late 1990s people were once again following this path to the crater rim. The lava surface is now soft, grey and sandy.
After having to turn back on the west slope on 27 June, the St. Lawrence University party reached the crater from the east side on 29 June and found its floor to be covered by dark, very fresh lava with both blocky and ropy textures. Much of the lava was still warm, and small pahoehoe flows were being extruded in some areas. Lava was spattering from a new vent (T23) close to T20 in the centre of the crater floor. The photographs below were taken from the air by Celia Nyamweru on 3 July 1993 and show the significant changes that had occurred since early June.
The activity appeared to have been centred at several vents on the southern part of the crater floor (the former 'Southern Depression'). These include two big ash rings at the base of the southern wall (T26 and T30, see the photograph to the left above), and a broken ash ring near the east wall which was the source of a very thick, blocky flow that J.B. Dawson later named 'Chaos Crags' (see the photograph to the right above). More details about the activity of 1993 are given in Nyamweru (1993, 1997). Analysis of Chaos Crags showed it to be very rich in crystals of nyerereite and gregoryite, the typical minerals of natrocarbonatite. However it also contained 8 to 10% by weight of spheroids (up to 2 mm in diameter) of dominantly silicate material. This unusual composition may be related to the very high viscosity of Chaos Crags and another flow formed at the same time. These flows seem to have been much more viscous than other flows at Oldoinyo Lengai, to the extent of being within the range for rhyolites (Dawson et. al 1994).

 

 

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