Morphology of Magnetic Minerals and Magnetic Susceptibility of Volcanic Ash from 2010 Eruption of Merapi Volcano, Indonesia

Abstract

The composition, morphology and magnetic susceptibility of the volcanic ash samples of Merapi volcano have been tested. The composition of elements in the samples was determined using X-Ray Fluorescence (XRF), magnetic minerals morphology was determined using Scanning Electron Microscopy (SEM) and magnetic susceptibility was determined using Bartington Magnetic Susceptibility meter MS2B. There are about 17 elements found in volcanic ash, with the largest percentage being silica (Si), which is around 45%; iron (Fe) element have a concentration of around 16% and aluminum (Al) around 12%. Meanwhile, other elements are in very low concentration. If it is used to track events related to the dynamics of the earth, that three elements can be used as proxy data. Based on the composition of Merapi volcanic ash, it is possible that the existing of magnetic minerals are dominated by iron titanium oxide. The size and shape of magnetic minerals are very diverse, ranging in size from tens to hundreds of micrometers. Meanwhile, the surface of the magnetic mineral also appears not smooth or porous. This condition is thought to occur due to heat with very high temperatures regarding magnetic minerals before and during the eruptions. Magnetic susceptibility measured at low frequency is in the range of 10 × 10-6 m3/kg for extract samples and 2200 × 10-6 m3/kg for non-extracted samples.