Searching for evidence of a global catastrophe in the East African Rift Basin: Did the Toba supereruption alter paleoflora at Gona, Ethiopia?

Project Abstract

Approximately 75,500 (+/- 900) years ago, the largest supereruption of the Late Pleistocene occurred in Sumatra, Indonesia. This explosion introduced ~1015 grams of fine ash into the atmosphere, produced ~3000 km3 of magma, and pyroclastic flows carpeted a ~105 km2 radius around the epicenter of the eruption. All flora and fauna within a 350 km radius were annihilated, and the enormous amount of ash that was aerosolized into the atmosphere is thought to have increased the Earth’s average albedo, which is speculated to be a possible catalyst for a period of global cooling.

The advent of the Toba supereruption coincides with a period of Anatomically Modern Human (AMH) migration out-of-Africa. While recent studies show that the effects from the “environmental catastrophe” observed in Sumatra likely did not significantly alter the environments of East Africa during this time, there are only two comprehensive studies of cryptotephra (microscopic ash) layers from the Toba volcano in the East African Rift System, only one of which focuses on the variability in vegetation pre- and post-eruption. Additionally, both of those studies are focused on localities in Lake Malawi, records of which are sourced from lacustrine cores. As AMH are terrestrial-based mammals, and only passively interact with lacustrine environments, the question then arises,

How did the vegetation in terrestrial areas with AMH activity change pre- and post-Toba supereruption?

The answer to this question may lie in the sediments and soils of Gona, Ethiopia, a significant paleoanthropological project area that contains an abundance of Early and Middle-to-Late Pleistocene archaeological and hominin fossil sites, fluvial sediments and soils, and a well-constrained chronostratigraphic record. Yaalu (11° 3' 51.55"N, 40° 25' 23.12"E), a paleoanthropological site in Gona, has strata that have been dated to 85-70ka.

During the 2020 field season, an undergraduate assistant and I will scout the area for an outcrop or series of outcroppings that encompass the full strata. Once a suitable site is located, a step-trench will be dug down-section to reveal the underlying strata. Individual soil horizons will be characterized, and oriented samples that encompass the full scope of the trench will be extracted. Sediment and soil samples will then be examined for evidence of cryptotephra, and phytoliths, silicic imprints of cellular structures from flora, will be extracted and characterized. Phytoliths will be point-counted, and percent relative abundance calculations will be derived from total phytolith count, alongside the starting dry weight. Namely, the tree cover and aridity indexes will be utilized, to see the change in low elevation semi-deciduous forests, and the expansion or contraction of riparian grass communities in the area.

This study will allow us to see examine the variability of flora (or lack thereof) at Gona during a critical period of early human development. If phytolith assemblages significantly change, or if the overall concentration of phytoliths decreases at Yaalu post-Toba, then one could infer that the Toba supereruption was a catalyst for, at the very least, minimal change within Gona’s ecosystem.



Funding Type

Research Grant

Academic College

Jesse D. Jones College of Science, Engineering and Technology


Earth and Environmental Sciences


MSc., Earth and Environmental Sciences




Gary Stinchcomb

Academic College

Jesse D. Jones College of Science, Engineering and Technology

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