Revisiting the Youngest Toba Tuff Super-Eruption: A high-resolution cryptotephra perspective from the Andaman Sea

Around 74,000 years ago, the largest known volcanic eruption of the Quaternary occurred at Toba volcano, in Sumatra, Indonesia: the Youngest Toba Tuff super-eruption (YTT). Its widespread ash deposits have long been used as chronostratigraphic markers in paleoenvironmental and archaeological studies. However, new evidence challenges the conventional view of the YTT as a single, short-lived cataclysmic event. Analysis of volcanic deposits from marine core BAR94–25, drilled off the northern coast of Sumatra, reveals that volcanic activity at Toba continued for a long period of at least ∼50 kyr (∼101 to ∼49 ka). Using high-resolution cryptotephra stratigraphy, textural observations, and in-situ geochemical analyses (EPMA, LA-ICP-MS), three distinct Volcanic Activity Phases (VAP1–VAP3) were identified: (i) VAP1 (∼101 to ∼79 ka) representing pre-YTT activity, (ii) VAP2 (∼75 to ∼65 ka) corresponding to the YTT phase, including multiple eruptions over ∼10 kyr (YTTs), and (iii) VAP3 (64 to ∼49 ka) marking post-YTT explosive activity associated with caldera resurgence. Each phase produced highly evolved rhyolitic magmas characteristic of Toba, with distinct geochemical signatures ( e.g. U/Th, Hf/Ta, Zr/Nb) indicating slight variations in late-stage differentiation from a common magmatic source. The YTT eruptions were fed by at least four compositionally distinct magma reservoirs, identified through Ba/Y and Sr/Y ratios of glass compositions, which were erupted simultaneously but in varying proportions throughout VAP2, rather than during a single event. This study highlights the need to reassess tephrostratigraphic correlations and the dating of sedimentary archives that rely on the traditional ∼74 ka YTT isochron. • High resolution reconstruction of last Toba supereruption using marine cryptotephra. • Toba volcanic Complex was active over a prolonged period (100–50 ± 5 ka). • Trace element compositions are crucial to distinguish Toba Volcanic Activity Phases. • Youngest Toba Tuff (YTT) eruption does not seem to be a single event ( i.e. ∼75 ka). • YTT supereruption consists of several eruptive events between 75 and 65 ka.