The December 22, 2018 Anak Krakatau, Indonesia, Landslide and Tsunami: Preliminary Modeling Results

Abstract

On the evening of December 22, 2018, the coasts of the Sunda Strait, Indonesia, were hit by a tsunami generated by the collapse of a part of the Anak Krakatau volcano. Hundreds of people were killed, thousands were injured and displaced. This paper presents a preliminary modeling of the volcano flank collapse and the tsunami generated based on the results of a 2D depth-averaged coupled model involving a granular rheology and a Coulomb friction for the slide description and dispersive effects for the water flow part.With a reconstructed total volume (subaerial and submarine) of the landslide of 150 million m 3 inferred from pre and post-collapse satellite and aerial images, the comparison of the simulated water waves with the observations (tide gauges located all around the strait, photographs and field surveys) is satisfactory. Due to the lack of information for the submarine part of the landslide, 2 Alexandre Paris et al. the reconstructed submarine slope is assumed to be approximately constant. A significant time delay on the results and particularly in the Bandar Lampung Bay could be attributed to imprecisions of bathymetric data. The sensitivity to the basal friction and to dispersive effects is analyzed through numerical tests. Results show that the influence of the basal friction angle on the simulated wave heights decreases with distance and that a value of 2°gives consistent results with the observations. The dispersive effects are assessed by comparing water waves simulated by a shallow water model and a Boussinesq model. Simulations with frequency dispersion produce longer wave periods and smaller wave amplitudes in the Sunda Strait and particularly in deep waters.

Field Survey of Tsunami Heights and Runups Following the 22 December 2018 Anak Krakatau Volcano Tsunami, Indonesia

“…Heidarzadeh et al (2020a) analyzed tide gauge records of the AKT and proposed a source model for this unique tsunami by applying numerical simulations; the source model proposed by Heidarzadeh et al (2020a) consists of an initial pure-elevation wave with height of 100-150 m and length of 1.5-2.0 km. The numerical modeling of the event by Paris et al (2020) and Zengaffinen et al (2020) further reconfirmed the source model initially proposed by Heidarzadeh et al (2020a). The volume of the sliding mass during the AKT was estimated at 0.2-0.3 km 3 by Ren et al (2020) whereas Heidarzadeh et al (2020a) reported it in the range of 0.175-0.326 km 3 .…”

Submarine landslide source models consistent with multiple tsunami records of the 2018 Palu tsunami, Sulawesi, Indonesia

“…It has reproduced well the run-up heights of tsunamis generated by submarine landslides in application to the case of Papua New Guinea earthquake in 1998 (Imamura and Hashi 2003). Pakoksung et al (2019) analyzed the 2018 Sulawesi earthquake using this type of model. The latter granular material models include Iverson and George (2014), Ma et al (2015), Grilli et al (2019) and Paris et al (2020), whose models' landslide part governed by Coulomb friction is originated from Savage and Hutter (1989).…”

“…Pakoksung et al (2019) analyzed the 2018 Sulawesi earthquake using this type of model. The latter granular material models include Iverson and George (2014), Ma et al (2015), Grilli et al (2019) and Paris et al (2020), whose models' landslide part governed by Coulomb friction is originated from Savage and Hutter (1989). Grilli et al (2019) and Paris et al (2020) applied this type of model to the case of Krakatau in 2018, demonstrating mass and tsunami behavior well.…”

“…The latter granular material models include Iverson and George (2014), Ma et al (2015), Grilli et al (2019) and Paris et al (2020), whose models' landslide part governed by Coulomb friction is originated from Savage and Hutter (1989). Grilli et al (2019) and Paris et al (2020) applied this type of model to the case of Krakatau in 2018, demonstrating mass and tsunami behavior well. Grilli et al (2019) also showed that tsunami waveforms at points far away from the source did not show much difference between the two models, dense Newtonian fluid model and granular material model.…”

“…Various tsunami sources have been modeled based on seismic data [Heidarzadeh et al (2019), using data from USGS (2018), Ulrich et al (2019)], Sentinel-2 satellite optical data (Jamelot et al 2019), Sentinel-1 satellite SAR images (Gusman et al 2019), and hypothetical submarine landslides (Pakoksung et al 2019). Although those studies compared calculated tsunami waveforms with the Pantoloan tide gauge record and tsunami heights determined by field surveys, a detailed comparison with tsunami heights over the entire bay has not been performed except for Ulrich et al (2019), and little quantitative consideration has been given to the video footage.…”