The use of pumice spatial distribution to determine the initial conditions and the ballistic effects of Samalas eruption

Abstract

Abstract Mount Barujari is an active volcano on Lombok Island located within the Mount Rinjani Complex. This spot is suspected of having had a massive eruption, hence the spread of pumice, with deposits assumed to have buried previously existing royal sites. The phenomenon of the distribution of volcanic sediments, especially pumice deposits, has not been studied qualitatively and quantitatively concerning the eruption dynamics in this complex. Therefore, the purpose of this research is to analyze the spatial distribution of pumice to determine the plume column dynamics and effects of the Samalas eruption 1257, and it was verified by the Kelud eruption in 2014. The results showed that the ballistic terminal velocity without atmospheric effects was 914.09 m/s, while the impact velocity was 955.50 m/s. These are both equivalents to 2.69 Mach (supersonic speed), resulting in a huge eruption explosion, which is heard up to a distance of 3000 km, often caused by the drag coefficient. Furthermore, the calculated drag coefficient shows the dynamics of current plume flow, including the transition zone between stable (Stoke’s Law) and turbulent flow (Newton’s Law). Simultaneously, the Samalas eruption’s kinetic energy was established as equivalent to 7 on the VEI scale. Therefore, it is necessary to examine the magma Chambers and their dynamics in the future.