| Penulis/Author |
Dr. Bachtiar Wahyu Mutaqin, S.Kel., M.Sc. (1) ; Franck Lavigne (2); Yayat Sudrajat (3); Lina Handayani (4); Pierre Lahitte (5); Clément Virmoux (6); Hiden (7); Dr. Danang Sri Hadmoko, S.Si., M.Sc (8); Jean-Christophe Komorowski (9); Nugroho D. Hananto (10); P. Wassmer (11); Prof. Dr. Hartono, DEA., DESS. (12); Kim Boilot Airaksinen (13) |
| Abstrak/Abstract |
One of the most powerful eruptions of the Holocene, known as the Samalas eruption, had a VEI of 7 and took place on Lombok, eastern Indonesia in 1257?CE. Thick tephra fall covered the entire island, and pyroclastic density currents (PDCs) up to 50?m thick buried almost half of Lombok. Until now, there has been no detailed study of the geomorphological evolution of Lombok related to this eruption, especially for the eastern part of Lombok. The main goal of this paper is therefore to reconstruct the paleo-topography on the eastern part of Lombok before the eruption of the Samalas volcano in 1257?CE, and to analyse the subsequent landscape evolution following this eruption. Data were collected from more than 1300 points in order to gather geomorphological, geological, and geochemical information for the eastern part of Lombok over the last millennium. Data were obtained from wells (which are widespread in the studied area), natural outcrops (mainly cliffs along the shoreline and the rivers), and human-made outcrops in quarries, as well as from the two-dimensional resistivity profiling (Dipole-dipole array) carried out on eastern Lombok in 2016 and 2017. We estimate that 4435?±?5.5?×?106?m3 of pumice-rich PDC, over a surface of 171?km2, buried the eastern part of Lombok in the aftermath of the 1257?CE eruption, and as a result of this rapid pumice-rich PDC deposition there has been some aggradation of the shoreline at some points, resulting in most of the pre-1257 coral reef being buried. After several intense rainfall events, the deposited volcanic material was probably eroded during the first decades following the 1257?CE eruption by mountain streams, producing lahars. We estimate that the remaining volume of pumice-rich PDC deposits following this erosion is 625?±?5.5?×?106?m3 over a surface of 89?km2, which is equivalent to 14% of the initial volume. |
