Late-Holocene mega-tsunamis in the Tasman Sea: an assessment of the coastal archaeological record of New South Wales

Abstract

Bryant and others have interpreted geomorphological and archaeological evidence from southcentral New South Wales (NSW) to infer repeated inundation of this coast by mega-tsunamis in late Holocene time. However, the stratigraphy of two well-dated archaeological sites (Pambula Lake, Bass Point) shows no evidence that these camps were abandoned, or that the marine component of the diet of local Aboriginal peoples changed at or about 500 or 1500 cal. BP, the time of the two most recent inferred mega-tsunamis. In addition, the mean probability distribution of the youngest calibrated radiocarbon ages from 52 archaeological sites on the southcentral NSW coast (grouped in three tsunami-susceptibility classes on the basis of site elevation and distance from the shore) does not differ from random expectations, and shows no evidence that sites were permanently abandoned in the aftermath of these inferred events. The mean probability distributions of calibrated radiocarbon ages from 108 charcoal samples from these sites does not differ from random expectations, and offers little support for the inference that the sites were temporarily abandoned about 500 or 1500 cal. BP. Probability distributions based on 70 marine shell ages show strong century-scale cyclicity, but this is likely too regular to be a product of mega-tsunamis. Moreover, changes in shellfish exploitation patterns and adoption of new fishing technologies by Aboriginal people on this coast do not coincide with the times of inferred tsunamis. The archaeological evidence offers no support for the hypothesis that mega-tsunamis inundated this coastline in the late Holocene.

A continental narrative: Human settlement patterns and Australian climate change over the last 35,000 years

“…As with other sectors, there is increasing diversification as diet broadens, which here is dominated by marine resources. Sites such as Bass Point midden (Sydney Basin) (Bowdler, 1976), Point Ritchie midden (Victoria Volcanic Plain) (Godfrey et al, 1996), Kendrick Park midden (Sydney Basin) (Australian Museum Business Services, 2003), MHE 8 (South East Corner) (Boot, 2002), Murrumarang midden (Sydney Basin) (Boot, 2002), Balmoral Beach 2 rockshelter (Sydney Basin) (Hutchinson and Attenbrow, 2009) and middens across South Eastern Queensland (Ulm et al, 1995) all show initiation, or re-activation, between ~4-3ka (see also Bird and Frankel, 1991a); and the number and spread of middens continue to increase in the last 2,000 years, suggesting resource intensification, although coastal stabilisation and preservation may be implicated (Ulm and Hall, 1996). A brief decline at ~3ka is also evident in regional studies for the south coast of NSW (Boot, 2002).…”

On the Possible Origins of an Unusual (Mid to Late Holocene) Coastal Deposit, Old Punt Bay, South-East Australia

“…One source of diverse, large shelly fauna often found on the coast is aboriginal middens (Hall and McNiven, 1999;Hutchinson and Attenbrow, 2009). It is unlikely that Unit 2 is a midden as it is much more extensive than any midden found on the coast (Hughes and Djohadze, 1980), contains no evidence of burning and contains several shells of inedible species.…”

“…The second has focused on sand sheets found in coastal embayments (Switzer et al ., 2005; 2006; Switzer and Jones, 2008a) that appear to be the result of much smaller, less frequent tsunamis. Despite the potential difference in frequency magnitudes, debate on the genesis of coastal overwash sand sheets found in coastal lagoons or boulders and coarse deposits on rocky coastlines and cliff tops (Felton and Crook, 2003; Switzer et al ., 2005; 2006; Dominey‐Howes et al ., 2006; Switzer and Jones, 2008a; Hutchinson and Attenbrow, 2009; Goff and Dominey‐Howes, 2010; Goff et al ., 2010a; 2010b; Switzer and Burston, 2010) continues and their presence in the landscape is indicative of high‐energy marine events along this coast.…”

Key issues in the conservation of the Australian coastal archaeological record: natural and human impacts

“…The impacts of tsunamis have been studied on many parts of the Australian and New Zealand coast (Bryant 2001;Goff and Dominey-Howes 2009;Nott 2004aNott , 2006b) and coastal Aboriginal middens may have been disturbed by such events (Bryant et al 1992;Fullager et al 1999). However, a recent comprehensive review of evidence from archaeological sites on the south-central New South Wales coast by Hutchinson and Attenbrow (2009) could find no support for the hypothesis that megatsunamis inundated the coastline in the late Holocene and the tsunami hypothesis must be treated with caution (Felton and Crook 2003). Surprisingly the recovery time from tsunamis may be quite short, as for example, following the 2004 Indian Ocean tsunami, which devastated coastal areas along the coast of Thailand and Sumatra (Liew et al 2010).…”