Toba ash layers in the South China Sea: Evidence of contrasting wind directions during eruption ca. 74 ka

Two cores from the southern South China Sea contain discrete ash layers tha t mainly consist of rhyolithic glass shards. On the basis of the SPECMAP ti me scale, the ash layers were dated to ca. 74 ka, the age of the youngest T oba eruption in northern Sumatra. This link is supported by the chemical co mposition of the glass, which is distinct from volcanic glass supplied from the Philippines and the northern South China Sea, but is almost identical with the chemistry of the Toba ash. The youngest Toba ash layers in the Sou th China Sea expand the previously known ash-fall zone over more than 1800 km to the east. The dispersal of ashes from Sumatra in both western and eas tern directions indicates two contrasting wind directions and suggests that (1) the Toba eruption probably happened during the Southeast Asian summer monsoon season, and (2) the volume of erupted magma was larger than previou sly interpreted.