Recurrent explosive eruptions from a high-risk Main Ethiopian Rift volcano throughout the Holocene

Abstract

Corbetti caldera is the southernmost large volcanic system in Ethiopia, and has been categorized at the highest level of uncertainty in terms of hazard and risk. Until now, the number and frequency of past explosive eruptions at Corbetti has been unknown, due to limited studies of frequently incomplete and patchy outcrop sequences. Here we use volcanic ash layers preserved in sediments from three Main Ethiopian Rift lakes to provide the first detailed record of volcanism for the Corbetti caldera. We show that lake sediments yield more comprehensive, stratigraphically resolved dossiers of long-term volcanism than often available in outcrop. Our eruptive history for Corbetti spans the past 10 k.y. and reveals eruptions at an average return period of ~900 yr. The threat posed by Corbetti has until now been underestimated. Future explosive eruptions similar to those of the past 10 k.y. would blanket nearby Awassa and Shashamene, currently home to ~260,000 people, with pumice-fall deposits, and would have significant societal impacts. A lake sediment tephrostratigraphic approach shows significant potential for application throughout the East African Rift system, and will be essential to better understanding volcanic hazards in this rapidly developing region.

Using Lake Sediment Cores to Improve Records of Volcanism at Aluto Volcano in the Main Ethiopian Rift

“…Fontijn et al, 2018; Figure 4). Their lower FeO content compared to all other samples, and relatively high SiO 2 , K 2 O, and Al 2 O 3 , match the composition of products of Corbetti volcano, the silicic center approximately 80 km south of Aluto, 50 km south of ABII, and 60-km south of LLIII (Fontijn et al, 2018;Martin-Jones et al, 2017). Their lower FeO content compared to all other samples, and relatively high SiO 2 , K 2 O, and Al 2 O 3 , match the composition of products of Corbetti volcano, the silicic center approximately 80 km south of Aluto, 50 km south of ABII, and 60-km south of LLIII (Fontijn et al, 2018;Martin-Jones et al, 2017).…”

“…Their lower FeO content compared to all other samples, and relatively high SiO 2 , K 2 O, and Al 2 O 3 , match the composition of products of Corbetti volcano, the silicic center approximately 80 km south of Aluto, 50 km south of ABII, and 60-km south of LLIII (Fontijn et al, 2018;Martin-Jones et al, 2017). year BP, which agrees with known periods of explosive activity at Corbetti, as constrained by tephra deposits found in lake sediment cores south west of Corbetti (Fontijn et al, 2018;Lamb et al, 2002;Martin-Jones et al, 2017). Modeled Oxcal ages indicate that ABII-08-16 was deposited between 5,410 and 5,980 cal.…”

“…There is also evidence of lower-magnitude postcaldera activity at the Tullu Fike complex immediately north of the caldera, which may be the source of late Quaternary pumice deposits located in the caldera walls (Fontijn et al, 2018;Mohr et al, 1980). It has produced several silicic Holocene eruptions, which have generated aphyric obsidian flows and/or pumice fall deposits and are documented in terrestrial sections and lake sediment cores up to 167 km from the volcano (Fontijn et al, 2018;Martin-Jones et al, 2017;Rapprich et al, 2016). It has produced several silicic Holocene eruptions, which have generated aphyric obsidian flows and/or pumice fall deposits and are documented in terrestrial sections and lake sediment cores up to 167 km from the volcano (Fontijn et al, 2018;Martin-Jones et al, 2017;Rapprich et al, 2016).…”

“…Bivariate plots of glass major element geochemistry. TT-6 a tephra layer in sediment core from lake Tilo (~100 km SW Aluto) and thought to be sourced from Aluto (afterMartin-Jones et al, 2017) is plotted as red stars. Reference glass geochemical data for Aluto and Corbetti fromFontijn et al (2018) shown in gray field.…”

Sustained Uplift at a Continental Rift Caldera

“…In the first scenario, at the observed rate of volume addition (10 7 m 3 /year) of parental basalt it would take 500–1,500 years to accumulate enough material to fractionate ∼5 × 10 8 m 3 of peralkaline magma (from ∼1.25 × 10 10 m 3 of intruded basalt; see Figure S2 for the distribution of peralkaline volumes and timescales given 90% and 96% fractionation and the volume change confidence thresholds). This time period encompasses the recurrence interval estimated by Martin‐Jones et al (). However, this implies that the current rate of volume change is continuous, which contrasts with previously observed periods of no deformation or subsidence (Biggs et al, ; Lloyd et al, ).…”