Multimethod Characterization of Volcanic Ashes from the Sunda Island Arc

Abstract

Compared to other countries in the world, Indonesia has the highest number of volcanoes; many of these volcanoes are located in the Sunda Island Arc. Considering their importance's as geological markers, identification of the sources of volcanic ashes is challenging and intriguing task. Standing on that reason, this study was aimed to characterize the magnetic and geochemical properties of several volcanic ashes from Sunda Island Arc to test whether these properties could serve as identifiers for the sources. This study used the ashes from Mount Sirung (in Pantar) and from Mounts Merapi and Slamet (in Java). The data would then be combined and compared with previous studies that used ashes from other volcanoes both inside as well as outside the Sunda Island Arc. The results showed that the magnetic susceptibility of Mounts Merapi and Slamet differed not too much, while that of Mount Sirung differed significantly due to low magnetic content. The plot of hysteresis parameters classified Mount Merapi into PSD domain and Mount Slamet into SP domain, while that of Mount Sirung could not be performed due to the weak signal obtained. Geochemical data also showed that ashes from Mount Sirung contained much lower concentration of Na2O + K2O compared to that in Mounts Merapi and Slamet. Each volcano had its distinct magnetic properties when these properties were compared to that of other volcanoes previously studied. The geochemical data also could reflect its magma properties regarding to its geological setting. It could be concluded that these multimethod approaches were able to differentiate volcanic ashes based on their sources.