The feeder system of the Toba supervolcano from the slab to the shallow reservoir.

Ivan Koulakov,Alexander Vasilevsky,Nikolai M Shapiro,Ekaterina Kasatkina,Sergey Smirnov,Nassir Al-Arifi,Claude Jaupart,Sami El Khrepy

doi:10.1038/ncomms12228

Abstract

The Toba Caldera has been the site of several large explosive eruptions in the recent geological past, including the world's largest Pleistocene eruption 74,000 years ago. The major cause of this particular behaviour may be the subduction of the fluid-rich Investigator Fracture Zone directly beneath the continental crust of Sumatra and possible tear of the slab. Here we show a new seismic tomography model, which clearly reveals a complex multilevel plumbing system beneath Toba. Large amounts of volatiles originate in the subducting slab at a depth of ∼150 km, migrate upward and cause active melting in the mantle wedge. The volatile-rich basic magmas accumulate at the base of the crust in a ∼50,000 km3 reservoir. The overheated volatiles continue ascending through the crust and cause melting of the upper crust rocks. This leads to the formation of a shallow crustal reservoir that is directly responsible for the supereruptions.

Highlights

The Toba Caldera has been the site of several large explosive eruptions in the recent geological past, including the world’s largest Pleistocene eruption 74,000 years ago
The topography of the Toba area is characterized by a large uplift with an average elevation of B1,500 m and lateral dimensions of 220 Â 100 km. This area is transected by the Great Sumatran Fault Zone (GSFZ), which can be clearly identified on the topographic map
In the context of the Toba volcanic activity, several important questions are actively debated: why did several large eruptions occur in approximately the same location in the Toba Caldera area? Why were the supereruptions followed by long periods of quiescence? Is the magma system beneath Toba active and can we expect a new supereruption of Toba in the near future? In this study, we analyse several types of observations, such as topographic/bathymetric maps, geoid transformations, seismicity distributions, and regional and local seismic tomography, and attempt to shed light on some of the above-mentioned questions

Summary

Introduction

The Toba Caldera has been the site of several large explosive eruptions in the recent geological past, including the world’s largest Pleistocene eruption 74,000 years ago. The most recent Toba supereruption, B74,000 years ago, is considered to be the largest terrestrial volcanic eruption of the Pleistocene[1,2]. This eruption ejected an enormous volume of material, with the dense rock equivalent estimated between 2,800 and 5,300 km[3] (refs 1,3). We can identify traces of the magma and volatile pathways in the mantle and two large magma reservoirs on the base of the Moho interface and in the upper crust, which are the major elements responsible for episodic occurrence of supereruptions

Methods

Results

Conclusion