Characterization of Sedimentary Features of the 2018 Palu Tsunami Event, Sulawesi, Indonesia

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.