The fall of volcanic material from Mount Lawu, Central Java: a case study of magnetic susceptibility

Abstract

Mount Lawu was recorded to have erupted last on November 28, 1885, releasing volcanic material including magnetic minerals. The material settles in various places carried by the wind and river flow. The movement of wind and river flow is very influential in the process of transporting volcanic material. Large material directly falls around the mountain, usually in the form of large rocks, and undergoes physical and chemical weathering. Small-sized materials such as volcanic ash and small-mass rocks will be carried by the wind and river flows in all directions. However, the displacement does not remove the magnetic minerals contained in it. Magnetic minerals can be evaluated by the method of rock magnetism using MS. Bartington MS2 device with a dependent MS2B sensor by mass. From this tool, the low field susceptibility values in the range of 1467.5 x 10−8 m3/Kg – 5262.1 x 10−8 m3/Kg and high field susceptibility in the range of 1467,1 x 10−8 m3/Kg. The volcanic material of Mount Lawu belongs to the Ilmenite (FeTiO3) group and belongs to the group of weak magnetism. Then further review the frequency-dependent susceptibility (%) to see the magnetic domains contained in the sample. From the magnetic susceptibility data, the percentage of frequency-dependent susceptibility (%) is less than 2%. From these data, the sample is not included in the superparamagnetic (SP) and in general the sample is classified as a multidomain item (MD).