Magnetic characterization of pyroclastic density current (PDC) of the A.D. 1257 eruption of Mt. Samalas, Lombok, Indonesia: preliminary results

Abstract

The 1257 AD Mt. Samalas eruption (Lombok, Indonesia) is one of the major volcanic eruption that causes global climate change and ejected thick layers (50 m) of pyroclastic density current (PDC). In this study, this PDC deposits from two different locations, namely Luk and Jugil, in the northern coast of Lombok were subjected to series of magnetic measurements that include mass-specific magnetic susceptibility, isothermal remanent magnetization (IRM) saturation, anhysteretic remanent magnetization (ARM) decay as well as hysteresis parameter. Prior to magnetic measurements PDC sample were sieved through to divide the samples into five different grain sizes, i.e., clay, silt, fine sand, coarse sand, and granule. Magnetic measurements were carried out for each grain size. The results show that the predominant magnetic mineral in all samples is PSD (pseudo-single domain) and MD (multidomain) magnetite. However, the mass-specific magnetic susceptibility of clay-size samples from Luk (∼ 501 × 10−8 m3/kg) differ significantly from that of Jugil (∼ 848 × 10−8 m3/kg) suggesting that although the deposits from Luk and Jugil were of the same sources, they likely to came from different eruptions events. So far, the concentration-dependent magnetic parameter, i.e., mass-specific magnetic susceptibility is still the best parameter to identified PDC deposits of Mt. Samalas based on their eruptive events.