History of scoria‐cone eruptions on the eastern shoulder of the Kenya–Tanzania Rift revealed in the 250‐ka sediment record of Lake Chala near Mount Kilimanjaro

Catherine Martin‐Jones,Thijs Van Der Meeren,Emma Tomlinson,Christian Wolff,Heather Moorhouse,Maarten Van Daele,Dirk Verschuren,Christine Lane

doi:10.1002/jqs.3140

Catherine Martin‐Jones, Thijs Van Der Meeren + Show 6 more

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https://doi.org/10.1002/jqs.3140

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Abstract

ABSTRACTReconstructions 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.

Highlights

Volcanism in East AfricaThe East African Rift system (EARS) marks one of Earth's best‐ preserved continental rift systems—a fascinating natural laboratory in which to study compositionally diverse volcanism and wide‐ranging volcanic hazards
This study focuses on nine basaltic tephras in the CHALLACEA and DeepCHALLA sequences (Table 1), which provide rare examples of far‐travelled tephra from scoria‐cone eruptions recorded in a lake‐sediment archive
The mafic tephras in Lake Chala are more alkaline than basalts erupted from the Kenya Rift volcanoes (Fig. 3), and more closely resemble basalts erupted from the off‐Rift volcanic centres of Mt Kilimanjaro and the Chyulu Hills

Summary

Introduction

Volcanism in East AfricaThe East African Rift system (EARS) marks one of Earth's best‐ preserved continental rift systems—a fascinating natural laboratory in which to study compositionally diverse volcanism and wide‐ranging volcanic hazards. Poppe et al, 2016; Campisano et al, 2017; Fontijn et al, 2018; McNamara et al, 2018) These tephrostratigraphic studies indicate that many volcanoes of the Kenya–Tanzania Rift erupted explosively during the Holocene, depositing ash over hundreds of kilometres (Fontijn et al, 2010, 2018; Martin‐Jones et al, 2017a,b; Lane et al, 2018; McNamara et al, 2018). Contemporary volcanism has occurred to the east of the Rift, with Mt Kenya, Mt Meru and Mt Kilimanjaro having erupted basalts alongside more differentiated nephelinite and phonolite compositions (Baker, 1987)

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