Runup, Inundation, and Sediment Characteristics of 22 December 2018 Indonesia Sunda Strait Tsunami

Abstract

Abstract. A tsunami caused by a flank collapse of the southwest part of the Anak Krakatau volcano occurred on 22 December 2018. The affected area of the tsunami included a coastal area located at the edge of Sunda Strait, Indonesia. To gain an understanding of the tsunami event, field surveys were conducted a month after the incident. The surveys included measurements of runup height, inundation distance, tsunami direction, and sediment characteristics at 20 selected sites. The survey results revealed that the runup height and inundation distance reached 7.8 m and 292.2 m, both was found at Site Cagar Alam, part of Ujung Kulon National Park. Tsunami propagated radially from its source and arrived in coastal zone with direction was between 25° and 350° from North. Sediment samples were collected at 27 points in tsunami deposits with a sediment thickness of 1.5–12 cm. The distance of the sediment deposit area from the coast was 40 %–90 % of the distance of the inundation caused by the tsunami. The highest elevation of deposits was 60 %–90 % of the highest runup. Sand sheets were sporadic, highly variable, and highly influenced by topography. Grain sizes in the deposit area were finer than those at their sources. The sizes ranged from fine sand to boulders, with medium sand and coarse sand being dominant. All sediment samples had a well sorted distribution. An assessment of the boulder movements indicates that the tsunami runup had minimum velocities of 4.0–4.5 m/s.