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.