Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria-cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250-ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non-visible (crypto-) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first-order age estimates for seven previously unknown eruptions. Long and well-resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years.
Bibliographical noteFunding Information:
This research was funded jointly by a UK Natural Environment Research Council standard grant (NE/P011969/1) and the International Continental Scientific Drilling Program through the DeepCHALLA project ( https://www.icdp‐online.org/projects/world/africa/lake‐challa‐kenya‐tanzania/ ). The authors thank the DeepCHALLA science team and Karen Fontijn for their contributions and discussion of ideas. Cryptotephra analyses were carried out in the Cambridge Tephra Laboratory, within the Department of Geography Science Laboratories at the University of Cambridge. Alma Piermattei and Friederike Murach‐Ward assisted with cryptotephra analysis, which were begun as part of an Early Career Fellowship from the Leverhulme Trust to CSL. Iris Buisman and Victoria Smith kindly supported EPMA analysis. We thank Karoly Németh and an anonymous reviewer for their suggestions, which greatly improved an earlier draft of this paper.
© 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd
Copyright 2020 Elsevier B.V., All rights reserved.
- Chyulu Hills volcanic field
- East African Rift
- Lake Chala
- Mount Kilimanjaro volcanic field
- tephra glass geochemistry
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