Long-range impacts of the ~74 ka Toba super eruption

Abstract

The ~74 ka Toba super eruption (Indonesia) was the largest Quaternary volcanic event and, thus, has been a topic of debate regarding its possible impact on climate, environment, and eventually, early modern humans. This dissertation was aimed at improving our understanding of the Toba impact by utilising cryptotephra as an absolute event marker of the eruption, resolving an age uncertainty issue that is persistent in proxy-based research in Quaternary sciences, eventually to be combined with palaeoecological methods for climatic and environmental reconstructions. Firstly, an ephemeral (lasting for <2 years) drying response to the Toba eruption is revealed in eastern equatorial Africa, which has been made possible by sub-annual-resolution proxy analysis on a sediment section bracketing Toba cryptotephra in Lake Chala (Tanzania/Kenya). Then, an up-to-date Toba tephra dataset is utilised to produce a modelled tephra thicknesses distribution map, which provides insight into selecting study sites with high potential for future Toba cryptotephra search, while the revised calculations of the eruption volume and volatile yields provide important constraints for assessing climatic and environmental impacts of the eruption. Furthermore, Toba cryptotephra is empirically searched from two rare distal lacustrine records (Chew Bahir and Lake Towuti) that span the timing of the eruption, but to no avail, highlighting the importance of considering taphonomy and ash dispersal in site selection for any future cryptotephra work. Finally, a ~120 ka cryptotephra from the Tondano caldera (Sulawesi, Indonesia) found alongside the Toba cryptotephra search is reported from Lake Towuti (Sulawesi, Indonesia), which attests to volcanological, paleoclimatic, and palaeoecological values of cryptotephra analysis.