Ernst, Gerald

Jacobs, Patric

KELLER, J

Kervyn de Meerendre, Matthieu

KLAUDIUS, J

MBEDE, E

English

Ghent University Academic Bibliography

Geophysical Research Abstracts, Vol. 8, 03814, 2006SRef-ID: 1607-7962/gra/EGU06-A-03814© European Geosciences Union 2006Debris avalanches at Oldoinyo Lengai (Tanzania):morphological evidence, collapse mechanisms andhazard assessmentM. Kervyn (1), J. Klaudius (2), J. Keller (2), E. Mbede (3), P. Jacobs (1), G.G.J.Ernst (1)(1) Mercator & Ortelius Research Center for Eruption Dynamics, Geology Dept, GhentUniversity, Belgium, (2) IMPG, Albert Ludwigs-University of Freiburg, Germany, (3)Department of Geology, University of Daar-es-Salaam, Tanzania(Matthieu.KervynDeMeerendre@UGent.be)Evidence for collapse scars and debris avalanches were collected in the field and sub-sequently fully documented and mapped using a combination of remote sensing dataincluding airphotos, SRTM DEM, ASTER and Landsat imagery. One debris avalancheestimated at∼5km3 in volume affected the Northern flank of Lengai and flowed north-ward at least 24 km, to the Southern shore of Lake Natron. This collapse, estimatedto have occurred at ∼10.000 B.P, affected more than 10% of the volcano volume. Thecollapse scar is a major unconformity in the volcano stratigraphy and correspondsto a transition from phonolite to nephenelite magma composition, accompanied by aNorthward shift of the feeding conduit. Remarkable linear alignments of individualhummocks are observed within the debris avalanche field and indicate flow direction.Evidence for at least two additional sector collapses affecting the N and E flanks ofOldoinyo Lengai are also documented. Of much smaller scale (∼0.1-0.2 km3), thesemost recent and shallow landslides are attributed to the unstable growth of the sum-mit part of the volcano. Lengai data is consistent with the greatest collapses occurringin the direction of the greatest height difference and least buttressing. Volcano-scalecollapses and debris avalanches are amongst the most hazardous volcanic phenom-ena. The potential for a future sector collapse at Lengai is also evaluated using RSdata and field observations. The Oldoinyo Lengai region is important for the localalready-threatened Masai herders and is an important focus for eco-tourism. The find-ings highlight the need to routinely monitor ground deformation and seismic activityat Oldoinyo Lengai to anticipate volcano collapse and/or an explosive eruption thatcould harm local people, unique ecosystems, international air traffic or developingeco-tourism.

Debris avalanches at Oldoinyo Lengai (Tanzania): morphological evidence, collapse mechanisms and hazard assessment

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Debris avalanches at Oldoinyo Lengai (Tanzania): morphological evidence, collapse mechanisms and hazard assessment

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