STUDY OF TSUNAMI DEPOSITS OF ANAK KRAKATAU VOLCANO ON DECEMBER 22, 2018 IN KALAPA KONENG AREA, PANDEGLANG REGENCY, BANTEN PROVINCE

• Main Author: Mujaddid, Ahmad
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/70587
• Institution: Institut Teknologi Bandung

There was a tsunami in the Sunda Strait on December 22, 2018 caused by a flank collapse triggered by the eruption of Anak Krakatau volcano. The tsunami waves contain sediment called tsunami deposits which laid on the land areas affected by the tsunami, one of which was in the Kalapa Koneng area, Pandeglang Regency, Banten Province. Research about those tsunami deposits is still limited. The study aims to determine the characteristics of tsunami deposits caused by a flank collapse based on megascopic observation, grain size (granulometry), chemical elements, foraminifera content, and cluster analyses. In addition, this study also compared the characteristics of tsunami deposits caused by a flank collapse, earthquake, and storm deposits. This research was conducted on one transect along 152 m with 13 location points of observation and sampling. Consisting of 45 sediment samples of tsunami deposits and pre-tsunami (soil) in total with the KLK code vertical sampling at a 1-cm interval according to the tsunami deposits thickness. This research was a part of the Indonesian Institute of Sciences' Geotechnology Research Center. The results of megascopic observations showed that the tsunami and pre-tsunami deposits (soil) had a clear erosional contact except for KLK06, KLK10, and KLK11. The megascopic characteristics of tsunami deposits were generally grayish brown, fine to coarse sand, poorly sorted, consists of plagioclase, quartz, biotite, calcite, magnetite, and fragments with a size of 0.5-2 cm consist of coral, mollusk shell, pumice, and lithic. Based on granulometry analysis, the tsunami deposits had a variety of sizes, from very coarse silt to coarse sand, poorly to very poorly sorted, and unimodal-bimodal. The elemental contents of Ca and Sr were relatively higher in the tsunami deposits compared to soil sediment which indicated the marine influence. Furthermore, the elements of Fe and Ti were relatively higher in the soil sediment compared to tsunami deposits indicated terrestrial source material. Based on foraminifera analysis, there were 25 species of benthonic foraminifera and were not found planktonic foraminifera. There was a mix environment between foraminifera association from shallow marine inner neritic and middle neritic. Moreover, based on cluster analysis, there were one to three layers in the tsunami deposit indicated the number of tsunami waves occurrence. Tsunami deposits caused by the volcanic flank collapse are able to be distinguished compared to tsunami deposits due to earthquakes and storm deposits from the parameters of sorting and layers contact beneath them. The distinguished parameters were not the common difference of the deposits but only based on the case study of tsunami deposits of Anak Krakatau 2018 in Kalapa Koneng and the references cited in this research.