NUMERICAL SIMULATION OF THE 2018 KRAKATAU TSUNAMI GENERATED BY FLANK COLLAPSE AND ASESSMENT OF TSUNAMI HEIGHT IN PANDEGLANG REGENCY

Abstract

This  study  aims  to  reconstruct  the  tsunami  event  on  December  22,  2018,  due  to  the  eruption  of  Anak  Krakatau Volcano, which caused a flank collapse and generated an underwater landslide. Then this landslide caused a  tsunami  that  impacted  the  coast  of  the  Sunda  Strait,  especially  on  the  coast  of  Pandeglang  Regency.  Based  on  satellite  imagery,  it  is  known  that  the  landslide  source  came  from  the  southwestern  part  of  Anak  Krakatau's  wall  moving down the former caldera wall of the 1883 Krakatau volcanic eruption. The mount grew again and was known as  Anak  Krakatau  Volcano  and  appeared  above  sea  level  in  1929  and  continued  to  grow.  Subsequently,  several  eruptions  spewed  sediment  deposits  that  had  accumulated  on  the  edges  and  foot  of  the  mount.  These  sediments  increased  and  became  unstable,  causing  flank  collapse  and  triggering  underwater  landslides.  Several  simulation  scenarios have been carried out to obtain the best model that can represent the 2018 Anak Krakatau Tsunami with landslide parameters, namely: the volume of the landslide is 0.276 km3, the duration of propagation is 410 seconds, the inclination angle is 8.2°, and the length of the landslide trajectory is 3435 meters. The waveform generated as a tsunami source is in the form of wave peaks in the direction of the slide and wave valleys on the back of the slide.  Furthermore, this wave propagated in all directions but primarily focused on the southwest, i.e., Panaitan Island and Pandeglang Regency. Tsunami simulations show that the tsunami reached: Panaitan Island and Pandeglang Regency at 58-60 minutes, Kota Agung (Lampung) at 42 minutes, and Ciwandan (Banten) at 46 minutes after the landslide with a tsunami height of 5.01m, 0.9 m, and 0.7 m respectively, with a maximum tsunami wave height of 18.6 m on Panaitan Island. Furthermore, it is known that five areas in Pandeglang Regency fall into the high tsunami hazard category with a tsunami height of more than 3 m, namely Panaitan Island, Ujungkulon District, Sumur, Panimbang, and  Labuhan.  By  accurately  knowing  the  distribution  of  tsunami  height  and  estimating  the  time  of  arrival  of  the  tsunami in the affected area and the inundation area, an early warning system and mitigation efforts can be planned, such as spatial planning and other actions.

Key words: Anak Krakatau tsunami, numerical simulation, flank collapse, underwater landslide, Pandeglang Regency