Exploring Regional Variability in Paleotsunami Deposits: Evidence from Bengkulu and Lampung, Sumatra

We conducted an extensive geohazard survey along 200 km of coastline in Bengkulu and Lampung provinces, Sumatra, Indonesia, focusing on paleotsunami deposits. Our study involved coring at 11 coastal sites, with a particular emphasis on exploring diverse coastal environments, including coralline shores behind reef platforms, coastal wetlands and river floodplains.  

 

 At the northern end of our study area, near Bintuhan, we documented a significant palaeo-tsunami deposit within a former coastal wetland now converted into a padi field. This deposit was clearly identified across several trenches in two transects separated by ~200 metres. At the southern end of the survey, we found abundant evidence of the 1883 Krakatoa eruption tsunami at three sites within Semangka Bay, directly facing Anak Krakatau volcano.  

 

 Interestingly, despite investigating numerous intermediate sites, we did not find any additional palaeotsunami evidence. This suggests possible regional variability in tsunami occurrence along this section of the Sumatran coastline. Our results raise the possibility that this region may not experience the same frequency or magnitude of tsunamigenic earthquakes as the Acehnese coastlines at the northern end of Sumatra, where there is now well-established evidence for large tsunamis recurring at approximately 500-year intervals. While we accept that it is possible that all seven sites we investigated in between, on the west coast of Lampung province, happened to have no preserved evidence, we raise the possibility that an alternative explanation is that this stretch of coastline does not experience earthquakes large enough to generate a tsunami that in turn has a wave high enough to be preserved in the coastal sediments. We believe that our study merits further investigation of the sedimentological record of paleotsunamis in this region, and the wider implications for regional seismicity characteristics.