Identification pyroclastic flow of magnetic minerals (Holocene volcano): A case study of paleo-volcano Lawu on the south side, Central Java, Indonesia

Abstract

Indonesia is surrounded by three tectonic plates: the Eurasian, Indo−Australian, and Pacific plates. The plates have caused Indonesia to have many volcanoes, both active and inactive, resting, or no longer active. One of the volcanoes belonging to the formed “Rest” category is the ancient Lawu volcano. The mountain is 10,000 radiocarbon years old or approximately 11,430 ​± ​130 calendar years ago, which is part of the Holocene age. The Lawu volcano erupted on November 28, 1885. This paper discusses the study of magnetic minerals in the case of pyroclastic flows originating from Mount Lawu. The values obtained in magnetic susceptibility are 47.53 ​× ​10−6 ​m3/kg to 79.41 ​× ​10−6 ​m3/kg. The results of this susceptibility measurement indicate the presence of igneous rocks resulting from pyroclastic flow. Furthermore, the vibrating sample magnetometer test showed an S−type (ferromagnetic) hysteresis curve, and the value of Mr/Ms (remanence ratio) define was below 0.5, which realized a multi-domain configuration. This ferromagnetic characteristic is attributed to the iron-based mineral (10.4%–17.1%) from the evaluation of X−Ray Fluorescence. The magnetite mineral confirmed in the X-Ray Diffractometer test is the largest source of magnetism in the sample.