Abstract
Abstract. An examination of the coastal geomorphology of bays along the Otago coastline, SE New Zealand, has identified a geomorphology consistent with tsunami inundation. A tsunami geomorphology consisting of a number of elements including dune pedestals, hummocky topography, parabolic dune systems, and post-tsunami features resulting from changes to the nearshore sediment budget is discussed. The most prominent features at Blueskin Bay are eroded pedestals although it is speculated that hummocky topography may be present in the bay. Tsunami geomorphology at Long Beach is more comprehensive with a marked association between pedestals and a hummocky topography. A full suite of potential geomorphological features however, is not present at either site. The type of features formed by a tsunami, and the ability to detect and interpret a tsunami geomorphology, hinges on the interaction between five key variables; sand availability, embayment type, nature of the coast, accumulation space, and landward environmental conditions. An appreciation of the geomorphic setting and history of a coast is therefore of fundamental importance when identifying what to look for and where to look for tsunami evidence. It is also important to realise that these features can also be formed by other processes.
Highlights
Prior to the Indian Ocean Tsunami (2004 IOT) of 26 December 2004, there had been a moderate amount of data collected concerning historically-documented events and the geological evidence of palaeotsunamis in Australia (e.g. Rynn, 1994; Bryant, 2001) and New Zealand (e.g. de Lange and Healy, 1986; Goff et al, 2001)
It is important to distinguish here between tsunami geomorphology and tsunami geology in the context of the Holocene sand dune environments discussed in this paper
This paper reports on work carried out on coastal geomorphology in New Zealand, where similar scour fan and breach features have been noted
Summary
Prior to the Indian Ocean Tsunami (2004 IOT) of 26 December 2004, there had been a moderate amount of data collected concerning historically-documented events and the geological evidence of palaeotsunamis in Australia (e.g. Rynn, 1994; Bryant, 2001) and New Zealand (e.g. de Lange and Healy, 1986; Goff et al, 2001). A previously reported, but little-used, geomorphic tsunami signature is called a “tsunami-scour fan” (Kitamura et al, 1961; Yulianto et al, 2007) It forms where a tsunami cuts a breach, or cleans out an existing one, through a dune ridge. Tsunami-scour fans were previously noted, on opposite sides of the Pacific Ocean, as products of the tsunami associated with the giant Chilean earthquake of 22 May 1960 They formed abundantly in northeast Japan by inflow and outflow where the 1960 tsunami cut breaches through roads and levees (Kitamura et al, 1961). This paper reports on work carried out on coastal geomorphology in New Zealand, where similar scour fan and breach features have been noted. The main goal of this work was to determine whether or not we could define a suite of features that could be termed a tsunami geomorphology, and if so, what criteria might control their presence or absence in the landscape
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