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We report the sediment features of the 2018 Palu tsunami in Indonesia based on the results of laboratory analysis. The mechanism for generating the 2018 Palu tsunami was a combination of an earthquake and a landslide, and several previous studies classified the tsunami as having a shorter wavelength and period. The characteristics of the deposits of tsunamis with shorter wavelengths and periods are not well recognized. We analysed samples of tsunami deposits along two transects on the east coast of Palu Bay. Grain size analysis showed that the deposits were generally fining upward along the transect, except for the seaward sites at Kayumalue. At both transects, grain sizes were mostly unimodally distributed. The organic and carbonate content in the tsunami deposits fluctuated, but in general the carbonates were higher in the tsunami deposits than in the pre-tsunami deposits. Organic matter tended to be higher in the pre-tsunami sediments. The content of geochemical elements also fluctuated. The content of foraminifera in the tsunami deposits was dominated by benthic species. The dominant sources of tsunami deposits were the transition to inner neritic zones, with minor contribution from pre-tsunami sediments. We conclude that the short-wave tsunami deposits of the Palu event are characterized by thin deposits with a dominant unimodal grain size distribution, sourced mostly from the shallow areas of Palu Bay. [ABSTRACT FROM AUTHOR]

On 22 December 2018, volcanic activity of Anak Krakatau, Indonesia, triggered a tsunami that caused more than 437 casualties on surrounding coastlines. Soon after the event, before the physical evidence of the tsunami disappeared, a postevent field survey was carried out. Measurements of tsunami inundation and impact are important to better model and understand the tsunami triggering processes to support future tsunami mitigation efforts. The impacted area on the western coast of Banten, Java Island, was surveyed to acquire tsunami inundation and run-up height data, together with field characteristics of the tsunami deposits. Data were acquired at 36 locations along three transects of tsunami deposits. From these, the maximum tsunami run-up height (up to 13 m) in the surveyed locations was identified on the southern part of the Banten Coast in the Tanjung Lesung area, an area located to the south of Anak Krakatau Volcano. The tsunami deposits were relatively thin along the transect, including a fining upward sequence without any clear evidence of fresh volcanic material, in disagreement with other reported volcano-induced tsunami deposits. Characteristics of the 2018 Anak Krakatau tsunami deposits are more similar to earthquake-induced tsunami deposits, hence complicating the paleotsunami reconstruction in Sunda Strait, where tsunami mechanisms are from both volcano and earthquakes along the Sunda subduction zone. [ABSTRACT FROM AUTHOR]

On 28 September 2018, a Mw 7.5 earthquake struck Sulawesi Island, soon followed by a destructive tsunami. This study provides a case history of tsunami deposition where submarine landslides or coastal collapses have contributed to and intensified tsunami generation. The sedimentary features resulting from this complex tsunami mechanism are not yet well understood. We surveyed tsunami deposits at six locations along the coastline of Palu Bay, in addition to measuring tsunami flow depth, run-up height, and inundation distance at each site. In general, the tsunami height was less than 8 m with a maximum inundation distance of 310 m. The tsunami deposits are thin with simple sedimentary structures such as fining upward sequences. These sedimentary characteristics are typical of tsunami deposits elsewhere around the world. This work is a preliminary study, in that numerical modeling including sediment transport has not been performed. Further work is needed to distinguish tsunamis with different source mechanisms. [ABSTRACT FROM AUTHOR]