Sinabung Volcano, located less than 25 miles from the northern edge of the Toba caldera, Sumatra, has been erupting dangerously since November, 2013 with significant potential hazard to the more the 100,000 people living in the surrounding Brestagi-Kabanjahe districts. 25 miles to the NE lies Medan, the capital of the North Sumatra province with over 2million people. Most concerning is that there is evidence that the erupted magma compositions of Sinabung and Sibayak (its neighbour) share more in common with the Toba magma system, than with other arc volcanoes in Suantra. Without trying to be alarmist, this affinity to Toba has obvious consequences for the way we should think about hazards from Sinabung and Sibayak as Toba-like compositions tend to result in more explosive eruptions that normal arc volcanoes. Moreover, if these two volcanoes are somehow linked to the Toba magma system, then we must factor that into predicting the potential hazard.
To test the hypothesis of a link between Sinabung-Sabayak and Toba magma systems, these researchers propose to look for a Toba ?signal? in Sinabung and Sibayak. The signal will be in two parts. First, they will focus on microscopic zircon crystals and obtain age dates that will help them identify any Toba-aged components. They will do this by obtaining in-situ U-Th age determinations in zircons and then combining these data with He-in-zircon. This will allow them to track the Toba signature back through the history of activity at Sinabung and Sibayak through time. In addition, detailed analysis of zonation of zircons would allow them to differentiate between two alternative explanations for the Toba signal; a) re-melting solidified remnants of Toba and b) rejuvenating an old Toba magma. Both these scenarios will influence the eruptive style of Sinabung and Sibayak, but the latter would connote that the Toba signal is recent and beneath Sinabung and Sibayak. Second, the chemical fingerprint of Toba will be searched for using whole rock major and trace elements, and isotopic ratios The work needs to be done in a timely fashion under the auspices of RAPID, while the iron is hot so to speak, because the opportunity to sample the most recent eruption must be taken before the explosive deposits, which are small, are removed by monsoon rains and their context lost. This work will be done in collaboration with Indonesian colleagues and other international groups addressing volcanic hazards from Sinabung.