Erosion and Sedimentation from the 17 July, 1998 Papua New Guinea Tsunami

Abstract

This paper describes erosion and sedimentation associated with the 17 July 1998 Papua New Guinea tsunami. Observed within two months of the tsunami, distinct deposits of a layer averaging 8-cm thick of gray sand rested on a brown muddy soil. In most cases the sand is normally graded, with more coarse sand near the base and fine sand at the top. In some cases the deposit contains rip-up clasts of muddy soil and in some locations it has a mud cap. Detailed measurements of coastal topography, tsunami flow height and direction indicators, and deposit thickness were made in the field, and samples of the deposit were collected for grain-size analysis in the laboratory. Four shore-normal transects were examined in detail to assess the shore-normal and along shore distribution of the tsunami deposit. Near the shoreline, the tsunami eroded approximately 10-25 cm of sand from the beach and berm. The sandy layer deposited by the tsunami began 50-150 m inland from the shoreline and extended across the coastal plain to within about 40 m of the limit of inundation; a total distance of up to 750 m from the beach. As much as 2/3 of the sand in the deposit originated from offshore. Across most of the coastal plain the deposit thickness and mean grain size varied little. In the along-shore direction the deposit thickness varied with the tsunami wave height; both largest near the entrance to Sissano Lagoon.

Tsunami geomorphology: Erosion and deposition from the 15 November 2006 Kuril Island tsunami

“…That the greatest erosion from tsunamis occurs closer to the shore is a common observation of post-tsunami surveys (cf. Gelfenbaum and Jaffe, 2003;Umitsu et al, 2007). Farther from the shore (hundreds of meters in the Ainu Bay case), patches of erosion typically occur where the topography generates local water acceleration, enhancing the erosive capacity of tsunamis.…”

“…Pre-tsunami and post-tsunami measurements of coastal geomorphology are necessary in order to calculate coastal change and sediment movement during a tsunami, topics of utmost interest to the tsunami community (cf. Gelfenbaum and Jaffe, 2003;Jaffe and Gelfenbaum, 2007;Huntington et al, 2007) and of broad interest to coastal geomorphologists (Dawson, 1994;Kench et al, 2008).…”

“…To date, the only quantifi ed before and after studies are beach profi les and atoll-island surveys from the 2004 Indian Ocean tsunami in southwestern India and the Maldives (Kurian et al, 2006;Kench et al, 2006Kench et al, , 2008. In addition, Gelfenbaum and Jaffe (2003) estimated depth of erosion by the 1998 Papua New Guinea tsunami from exposed tree roots.…”

“…Tsunamis remove vegetation and damage human-made structures (Dawson, 1994;Maramai and Tinti, 1997). Tsunami erosion causes beach retreat either as large-scale scour features or as smaller scallops (Dawson, 1994;Gelfenbaum and Jaffe, 2003;Kench et al, 2006;Kurian et al, 2006;Umitsu et al, 2007;Choowong et al, 2007). Tsunamis breach beach berms and other ridges, or erode the surface uniformly (Andrade, 1992;Dawson, 1994;Maramai and Tinti, 1997;Gelfenbaum and Jaffe, 2003;Choowong et al, 2007;Umitsu et al, 2007).…”

The Papua New Guinea tsunami of 17 July 1998: anatomy of a catastrophic event

“…7) explains the timing and location (3 km offshore) of the loud bang, and the northern horizon lit by the setting sun as reported by eyewitnesses on the sand spit before tsunami attack. Wave breaking also explains the highly localized erosional features observed on the lagoon side of the sand spit (Gelfenbaum and Jaffe, 2003). Figure 7 indicates that the first wave occurred more as a flood inundation, whereas the second wave was highly nonlinear throughout much of its inundation.…”