The late Quaternary eruptive history of Meru volcano, northern Tanzania

摘要

Mt. Meru, in the northern Tanzania divergence zone within the East African Rift System, is a historically active volcano, with its last eruption in 1910 CE. The flank deposits of Meru are dominated by lava flows, debris avalanche deposits as well as major pyroclastic formations indicative of Plinian-style eruptions. The stratigraphy, spatial extent, and chronology of these pyroclastic deposits have, however, not been systematically studied. Here we report on the detailed reconstruction of the stratigraphy and eruptive dynamics of Late Quaternary Meru explosive eruptions, based on field investigations, geochronological and geochemical analyses. The findings indicate that Meru had at least three moderate-to-large-scale explosive eruptions over the past 40,000 years. The oldest Meru explosive event we recognize (MXP1) generated pyroclastic density currents (PDCs), while the second (MXP2) and the third, most intense explosive event (MXP3) generated both pyroclastic fallout and PDCs. Conventional radiocarbon dating of 6 palaeosols underlying MXP2 and MXP3, dated at similar to 34.1-38.5 ka cal BP and similar to 31.5-36.9 ka cal BP respectively, suggest these two eruptions may have followed each other relatively close in time. The compositional range of pumice lapilli of both MXP2 and MXP3 is limited to tephriphonolite-phonolite. Dispersal and thickness data of the better preserved and larger MXP3 deposits suggest a minimum bulk volume of 2.5 km(3) of pumice fallout and 1.2 km(3) of PDCs, respectively, which corresponds to a total erupted mass of at least 2.7 x 10(12) kg and a magnitude of 5.4. Similar large-scale eruptions in the future would have a considerable impact on the nearby large urban population in Arusha city and its suburbs. This new information is, therefore, vital for the long-term volcanic hazard assessment in Northern Tanzania. (C) 2021 Elsevier B.V. All rights reserved.