Bulletin of Volcanology

, Volume 72, Issue 8, pp 893–912 | Cite as

Fundamental changes in the activity of the natrocarbonatite volcano Oldoinyo Lengai, Tanzania

I. New magma composition during the 2007–2008 explosive eruptions
  • Jörg KellerEmail author
  • Jurgis Klaudius
  • Matthieu Kervyn
  • Gerald G. J. Ernst
  • Hannes B. Mattsson
Research Article


With a paroxysmal ash eruption on 4 September 2007 and the highly explosive activity continuing in 2008, Oldoinyo Lengai (OL) has dramatically changed its behavior, crater morphology, and magma composition after 25 years of quiet extrusion of fluid natrocarbonatite lava. This explosive activity resembles the explosive phases of 1917, 1940–1941, and 1966–1967, which were characterized by mixed ashes with dominantly nephelinitic and natrocarbonatitic components. Ash and lapilli from the 2007–2008 explosive phase were collected on the slopes of OL as well as on the active cinder cone, which now occupies the entire north crater having buried completely all earlier natrocarbonatite features. The lapilli and ash samples comprise nepheline, wollastonite, combeite, Na-åkermanite, Ti-andradite, resorbed pyroxene and Fe–Ti oxides, and a Na–Ca carbonate phase with high but varying phosphorus contents which is similar, but not identical, to the common gregoryite phenocrysts in natrocarbonatite. Lapilli from the active cone best characterize the erupted material as carbonated combeite–wollastonite–melilite nephelinite. The juvenile components represent a fundamentally new magma composition for OL, containing 25–30 wt.% SiO2, with 7–11 wt.% CO2, high alkalies (Na2O 15–19%, K2O 4–5%), and trace-element signatures reminiscent of natrocarbonatite enrichments. These data define an intermediate composition between natrocarbonatite and nephelinite, with about one third natrocarbonatite and two thirds nephelinite component. The data are consistent with a model in which the carbonated silicate magma has evolved from the common combeite–wollastonite nephelinite (CWN) of OL by enrichment of CO2 and alkalies and is close to the liquid immiscible separation of natrocarbonatite from carbonated nephelinite. Material ejected in April/May 2008 indicates reversion to a more common CWN composition.


Oldoinyo Lengai Explosive eruptions 2007–2008 paroxysms New silicate magma composition Carbonated nephelinite 



Access to the summit of Oldoinyo Lengai had become difficult since the paroxysm of 4 September 2007. Tim Leach from Ngare Sero Lodge explored and opened, together with local Maasai, a new route from the east–southeast. The expedition of 7 December 2007 used this route with the help of the Maasai guides Saringe, Tumba, and Lekoko from Engare Sero. This logistic support is gratefully acknowledged. We thank Benoît Wihelmi, Tim Leach, and Tom Pfeiffer for providing and granting permission to use some of their spectacular pictures. Julie Albaric, Evelyne Pradal, and Chris Weber contributed the additional samples of November 2007 and February 2008 ashes and lava bombs of April 2008, respectively. We also thank all who contributed with observations and photographs, which enabled to follow the activity evolution from distance. This includes in particular Thomas Holden, Jens Fissenebert, and Chris Weber. We acknowledge stimulating discussions with Barry Dawson, Roger Mitchell, and Bruce Kjarsgaard. Research of JKe and JKl at OL is supported by DFG project Ke 136/40. MK and GGJE are supported by postdoctoral grants of the Fonds voor Wetenschappelijk Onderzoek-Vlaanderen. Melanie Schrage, Sigrid Hirth-Walther, Isolde Schmidt, and Dagmar Flemming of MGI Freiburg were of invaluable help in sample and thin section preparation and chemical analyses. Hiltrud Müller-Sigmund gave expert advice at the electron microprobe. Jörg Erzinger of GFZ Potsdam is thanked for his spontaneous availability when asked for additional fluorine and chlorine determinations. The paper greatly benefited from the careful, competent, and constructive reviews by Barry Dawson and Bruce Kjarsgaard.


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Jörg Keller
    • 1
    Email author
  • Jurgis Klaudius
    • 1
    • 4
  • Matthieu Kervyn
    • 2
  • Gerald G. J. Ernst
    • 2
  • Hannes B. Mattsson
    • 3
  1. 1.Institut für Geowissenscahften, Mineralogie–GeochemieAlbert-Ludwigs-Universität FreiburgFreiburgGermany
  2. 2.Mercator and Ortelius Research Centre for Eruption Dynamics, Department of Geology and Soil ScienceGhent UniversityGhentBelgium
  3. 3.Institute of Geochemistry and PetrologyETH Zürich, Swiss Federal Institute of TechnologyZurichSwitzerland
  4. 4.Terratec Geophysical ServicesHeitersheimGermany

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