Activity: 1968-1983

In 1968 the summit crater consisted of a larger northern sector centred on a deep pit crater, separated by a transverse ridge (the Saddle) from the shallower ash filled Southern Depression. The photograph to the left was taken by J.B. Dawson in 1969. Looking eastwards, it shows the pit crater on the left, the Saddle in the centre and the Southern Depression to its right. Fumarolic activity continued during these years, and the smell of sulphur from the crater was so strong that it could be detected from an overflight in a light aircraft. There are no records of activity between 1968 and 1983. From January to March 1983 a number of small ash eruptions occurred; in mid-February there was a slight fall of fine grey ash at Olduvai Gorge, 65 km to the west. John Fanshawe and Harvey Croze took photographs from the air in early April 1983; see photograph to the right. There was a lava flow reaching about two thirds across the floor of the pit crater and two small black cones with open vents at the base of the north wall.

Since then the crater has been progressively filled with lava flows and spatter cones. By early 1984 the pit crater was almost full (upper photograph to left, taken by Fred Trott in June 1984), and the level of the crater floor reached the base of the upper ash slopes between July and October 1984 (lower photograph to left, taken by Markus Borner in October 1984). Throughout this period, all activity occurred in the northern sector; there was no activity south of the Saddle.

There were several eruptions from vents on the inner (north) walls of the crater and a small cone was built on the north rim; see photograph below, taken by Andy Nyblade in November 1987.

Between July and October 1988 lava began to flow southwards across the Saddle into the Southern Depression. The photograph to the left below was taken from the southern summit by Martin Smith in October 1988 and shows how lava (already white when this photograph was taken in October 1988) has spilled over the Saddle and begun to fill the floor of the Southern Depression. The photograph to the right was taken by Celia Nyamweru about a month later and looks almost due east along the Saddle. A large vent (T11) has opened just north of the saddle and during our visit to the crater we observed lava flowing southwards from this vent on several occasions. At times when the hot lava came into contact with vegetation on the slopes around the Southern Depression it started small brush fires.

Activity continued within the crater in the early 1990s. Lava cones built up at different locations on the crater floor. The photograph to the left below, taken by Celia Nyamweru in August 1990, shows T14 which was active in August 1990; note the contrast between the white side of the cone which is several months old and the fresh black material that was being erupted as the photograph was taken. Lava flows continued to build up the level of the crater floor and to flood across the former line of the Saddle, creating a single oval crater in place of the former northern pit crater and southern depression. The photograph to the right below was taken by Lester Eshelman in July 1990, a period when there was a lot of fresh lava in the crater. Several flows seem to originate from the large dark cone (T5T9) in the foreground and have flowed to the north and southwest walls of the crater.

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