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Eruptive history of the Oldoinyo Lengai volcano: Constraints on the stratigraphic record in northern Tanzania with implications for volcanological and anthropological research

English title Eruptive history of the Oldoinyo Lengai volcano: Constraints on the stratigraphic record in northern Tanzania with implications for volcanological and anthropological research
Applicant Mattsson Bjoern Hannes
Number 140560
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.01.2013 - 31.12.2016
Approved amount 267'046.00
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All Disciplines (4)

Discipline
Geochemistry
Geochronology
Other disciplines of Earth Sciences
Mineralogy

Keywords (6)

Olduvai gorge; Explosive volcanism; Geochronology; East African Rift; Volcanic hazards; Oldoinyo Lengai

Lay Summary (English)

Lead
Lay summary

Oldoinyo Lengai volcano is the only currently active volcano in the East African Rift System of northern Tanzania, and it has been the source of at least five explosive eruptions in the last 100 years. Despite the recent eruptions very little is known about the eruptive history of the volcano as a whole, and there are only a handful age determinations published in the literature. Based on the explosive behavior of the volcano and the many ash-layers found at other locations in northern Tanzania (e.g. Olduvai Gorge, Laetoli and Peninj sites), it has been suggested that some of these ash-layers (interbedded with hominid remains) may be derived from Oldoinyo Lengai. Oldouvai Gorge, Laetoli and Peninj are some of the most important archeological sites in the world, which have been instrumental in furthering the understanding of early human evolution. However, due to a lack of stratigraphic profiles covering the area in-between Oldoinyo Lengai and the studied sites, conclusive evidence for the volcanic source(s) of the ash layers is missing. Therefore, this project aims to close this informational gap by:

(1) Measuring a dense network of stratigraphic logs in a sector extending SW-NW of Oldoinyo Lengai (i.e., along the prevailing wind directions).

(2) Combining grain-size distributions, bulk rock chemistry and detailed mineral chemistry to characterize the sampled ash-layers.

(3) Measure the Anisotropy of Magnetic Susceptibility in samples from the different ash layers and use the results as a proxy to infer depositional directions.

(4) Date the major eruptive episodes using a combination of different radiometric techniques.

By combining the data listed above this project we aim to pinpoint exactly which (if any) ash-layers, in the various stratigraphic profiles in northern Tanzania, are derived from Oldoinyo Lengai volcano. From the thickness and spatial variability of the ash-layers the volumes of magma associated with each eruption can be calculated. Radiometric age determinations of potassium-bearing minerals and plant remains found in the ashes allows for recurrence rates of volcanic eruptions to be calculated and any changes in the volcano's eruptive behavior with time will be recorded.

In combination, the data from this project will serve as the fundamental basis for a detailed hazard assessment of the volcano. Establishing a detailed eruption history also has important implications for anthropological research on the early human evolution by better constraining the volcanic source(s) and absolute ages of the ash layers.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
The Lake Natron Footprint Tuff (northern Tanzania): volcanic source, depositional processes and age constraints from field relations
Balashova Anna, Mattsson Hannes B., Hirt Ann M., Almqvist Bjarne S. G. (2016), The Lake Natron Footprint Tuff (northern Tanzania): volcanic source, depositional processes and age constraints from field relations, in JOURNAL OF QUATERNARY SCIENCE, 31(5), 526-537.

Associated projects

Number Title Start Funding scheme
129985 Fragmentation, eruption dynamics and depositional processes in mixed carbonatite - silicate volcanic eruptions 01.08.2010 Project funding (Div. I-III)
150629 Long core SQUID Rock Magnetometer: High-resolution lake studies, assessing efficacy of drug targeting, and the search for magnetic monopoles 01.12.2013 R'EQUIP
144421 Fragmentation, eruption dynamics and depositional processes in mixed carbonatite - silicate volcanic eruptions 01.10.2012 Project funding (Div. I-III)

Abstract

This proposal focuses on the only active volcano in the East African Rift System of northern Tanzania, i.e. Oldoinyo Lengai. The volcano rises more than 2000 m above the surrounding rift plain and has been the source of five major explosive events during the last 100 years. Despite the recent explosive eruptions very little is known about the eruptive history of the volcano and there are only a handful age determinations published in the literature. Based on the explosive behavior of the volcano over the last 100 years and the many ash-layers found at other locations in northern Tanzania (i.e. Olduvai Gorge, Laetoli and Peninj sites), it has been suggested that some of these ash-layers (interbedded with hominid remains) may be derived from Oldoinyo Lengai. These are some of the most important archeological sites in the world, which have been instrumental in furthering the understanding of early human evolution. However, due to a lack of stratigraphic profiles covering the area in-between the volcanoes and the studied sites, conclusive evidence for the volcanic source(s) is missing. Therefore, this Ph.D.-project aims to close this informational gap by:(1)Measuring a dense network of stratigraphic logs in a sector extending SW-NW of Oldoinyo Lengai.(2)Combining grain-size distributions, bulk rock chemistry and detailed mineral chemistry to characterize the sampled ash-layers.(3)Measure the Anisotropy of Magnetic Susceptibility in samples from the different ash layers and use the results as a proxy to infer depositional directions.(4)Date the major eruptive episodes using a combination of 40Ar-39Ar and 14C techniques.By combining the data listed above this project will be able to pinpoint exactly which (if any) ash-layers, in the various stratigraphic profiles in northern Tanzania, are derived from Oldoinyo Lengai. From the thickness and spatial variability of the ash-layers, isopach maps can be drawn and the volumes of magma associated with each eruption can be calculated. Radiometric age determinations (40Ar-39Ar and 14C) of sanidine crystals and plant remains in the ashes, conducted on a collaborative/commercial basis, allows for recurrence rates of volcanic eruptions to be calculated and any changes in the eruptive behavior with time will be recorded. In combination, the data from this project will serve as the fundamental basis for a detailed hazard assessment of the volcano. Establishing a detailed eruption history also has important implications for anthropological research on the early human evolution by better constraining the source and absolute ages of the ash layers. Here we request a SNF research grant to cover expenses of one PhD student (salary, travel and laboratory costs), as well as part of our own field expenses.
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