The late Quaternary eruptive history of Meru volcano, northern Tanzania

Abstract

Mt. Meru, in the northern Tanzania divergence zone within the East African Rift System, is a 14 historically active volcano, with its last eruption in 1910CE. The flank deposits of Meru are dominated 15 by lava flows, debris avalanche deposits as well as major pyroclastic formations, indicative of Plinian-16 style eruptions. The stratigraphy, spatial extent, and chronology of these pyroclastic deposits have, 17 however, not been systematically studied. Here we report on the detailed reconstruction of the 18 stratigraphy and eruptive dynamics of Late Quaternary Meru explosive eruptions, based on field 19 investigations, geochronological and geochemical analyses. The findings indicate that Meru had at 20 least three moderate-to-large-scale explosive eruptions over the past 40,000 years. The oldest Meru 21 explosive event we recognize (MXP1) generated pyroclastic density currents (PDCs), while the second 22 (MXP2), and the third, most intense explosive event (MXP3), generated both pyroclastic fall and 23 PDCs. Conventional radiocarbon dating of 6 palaeosols underlying MXP2 and MXP3, dated ~34.1-24 38.5 kacalBP and ~31.5-36.9 kacalBP respectively, suggesting they may have followed each other 25 relatively close in time. The compositional range of pumice lapilli of both MXP2 and MXP3 is limited 26 to tephriphonolite-phonolite. Dispersal and thickness data of the better preserved and larger MXP3 27 deposits suggest a minimum bulk volume of 2.5 km 3 of pumice fallout and 1.2 km 3 of PDCs, 28 respectively, which corresponds to a total erupted mass of at least 2.74×10 12 kg and a magnitude of 29 5.4. Similar large-scale eruptions in the future would have considerable impacts on the nearby large 30 urban population in Arusha city and its suburbs. This new information is, therefore, vital for the long-31 term volcanic hazard assessment in Northern Tanzania.

Hydrochemical Characterisation of High-Fluoride Groundwater and Development of a Conceptual Groundwater Flow Model Using a Combined Hydrogeological and Hydrochemical Approach on an Active Volcano: Mount Meru, Northern Tanzania

“…Most rocks within the area are Pleistocene volcanic-sedimentary sequences, but older sequences date back to the Miocene-Pliocene [4,23,24,27]. The lithology in the study area is dominated by volcanic rocks lava flows, pyroclastic, and debris avalanche deposits from the Mount Meru, with some alluvium, alluvial fan, and lake deposits found around the volcano base (Figure 3).…”

Retrieval of refractive indices of ten volcanic ash samples in the infrared, visible and ultraviolet spectral region

“…In this study, a total of ten volcanic ash samples from tephra fall deposits spanning a range of chemical compositions were selected: a medium-K basaltic andesite from an 18th century eruption at the Main Crater Taal volcano (Philippines; Delos Reyes et al, 2018), a phonolite from the MXP3 deposit of Mt Meru (Tanzania; Kisaka et al, 2021), a trachyte from the Isongole Pumice deposit of Rungwe volcano (Tanzania; Fontijn et al, 2010) and a peralkaline rhyolite from a Late-Holocene eruption at Corbetti volcano (Ethiopia; Fontijn et al, 2018). These samples were deliberately selected to cover a range of compositions, especially alkaline, to be representative for eruptions in East Africa, and which are known to be potentially highly explosive (Fontijn et al, 2010(Fontijn et al, , 2018Kisaka et al, 2021). Samples of the historical eruptions of Pinatubo in 1991 and Mount Saint Helens has been also chosen due to their large impact on the climate in twentieth century.…”