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Report on Ol Doinyo Lengai (Tanzania) — 17 August-23 August 2005

Ol Doinyo Lengai

Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
17 August-23 August 2005
Managing Editor: Gari Mayberry

Please cite this report as:

Global Volcanism Program, 2005. Report on Ol Doinyo Lengai (Tanzania). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 17 August-23 August 2005. Smithsonian Institution and US Geological Survey.

Weekly Report (17 August-23 August 2005)

Ol Doinyo Lengai


2.764°S, 35.914°E; summit elev. 2962 m

All times are local (unless otherwise noted)

During a trip to Ol Doinyo Lengai by Fred Belton during 19 July to 9 August, three eruptions occurred at cone T58C on 20 and 21 July, one of which lasted 20 hours. No further eruptions were observed through 9 August. The most recent eruption prior to 20 July occurred on 9 July when large lava flows completely covered the campsite in the E part of the crater. Photos indicated that there may have been infrequent activity at the volcano at least as long ago as 15 May. No new cones had formed at the volcano since 15 July 2004 when T58C was created.

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.

Source: Ol Doinyo Lengai (Fred Belton)