Abstract
Super-eruptions, orders of magnitude larger than eruptions experienced in historic times, have devastated wide areas by pyroclastic flows, covered continent-size areas by ash fallout, and injected large quantities of aerosols into the stratosphere affecting global climate. The Youngest Toba Tuff (YTT) is the largest known super-eruption in the Quaternary. Here we reconstructed the ultra-distal volcanic ash dispersal during this super-eruption using a computational ash dispersal model, which provides insights into the eruption dynamics and the impact of the event. The method uses a 3D time-dependent tephra dispersion model, a set of wind fields, and several tens of thickness measurements of the YTT tephra deposit. Results reveal that the YTT eruption dispersed ~8600 km3 (~3800 km3 dense rock equivalent, DRE) of ash, covering ~40 million km2 with more than 5 mm of ash. These new fallout volume estimations indicate that the total volume of the material erupted (including the massive pyroclastic density current, 1500 km3 DRE, deposits on Sumatra) was ~5300 km3 DRE. Simulation results indicate that the eruption had a very large mass flow rate and that the umbrella cloud, associated with the eruption plume, spread as an enormous gravity current around the neutral buoyancy level. The YTT tephra forms a key chronostratigraphic marker in the sedimentary sequences, and is particularly useful for constraining the age of the palaeoenvironmental and archaeological records, and synchronizing these archives to investigate temporal relationships. These new constraints on the extent of the YTT deposit are therefore particularly useful for cryptotephra studies that aim to find non-visible tephra layers for these chronological purposes. This method used to constrain volcanological parameters of eruptions in the past provides insights into the dispersal processes, and allows the amount of volatiles released to be estimated which is crucial to assessing the impact of such events.
Highlights
Our knowledge of the volume and dispersal of large eruptions in the past, and their impact, is based on the observations of the volcanic deposits preserved and exposed (e.g., Self, 2006)
Considering volume estimations of ∼1500 km3 dense rock equivalent (DRE) for the proximal pyroclastic density current (PDC) deposits, and some of the caldera infill that would have been associated with the PDC (Chesner and Rose, 1991), the total bulk volume of the Youngest Toba Tuff (YTT) eruption is ∼13200 km3 (5300 km3 DRE)
The mean error on the total mass associated to tephra fallout is about a factor 1.5, which implies the volume of magma eruption could have been between 2000 and 6000 km3 (DRE)
Summary
Our knowledge of the volume and dispersal of large eruptions in the past, and their impact, is based on the observations of the volcanic deposits preserved and exposed (e.g., Self, 2006). We use a tephra dispersal model, a range of wind fields, and all the known thickness observations to further constrain the magnitude of large super-eruptions and gain some insight into eruption processes. This method was applied to the largest known eruption in the Quaternary, the Youngest Toba Tuff (YTT). Rose and Chesner (1987) estimated the minimum mass of the ash fall deposit to be 800 km dense rock equivalent (DRE). Because the limitations of the approach and limited tephra thickness dataset used in Matthews et al (2012), the ultimate distribution of the tephra deposit and estimations of erupted volume and www.frontiersin.org
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