Alex van Leerdam flew over the volcano 28 June and took a short video film of the N crater. His view was from the N and did not show the extreme N or E crater floor or inner walls. All lava on the visible portion of the crater floor was at least a few weeks old and generally pale, with a large, slightly darker area to the W that covered the former T2 cone and its surroundings. The patch of lava (F8) that formed in November 1988, S of the former saddle (13:12), was white and seemed to have enlarged slightly since December 1988 (although it had appeared unchanged in 12 January photographs). The flow that had breached the saddle in November 1988 had widened since December, and only small parts of the saddle's upper slope remained visible. Cones T11, T8, T4/T7, and T5/T9 on the crater floor were pale in color. The rim cone (C1) appeared almost unchanged, and apparently no new major cones had formed since December 1988.

Geological Summary. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Information Contacts: C. Nyamweru, Kenyatta Univ; A. van Leerdam, Nairobi, Kenya.