Younghusband Peninsula Research Articles

The Formation of Deflation Ridges

The deposition of both pumice and shell is common on beaches during calm and storm wave conditions. This paper describes an investigation of pumice and shell ridges at two sites in Australia, Dark Point in NSW, and in the Younghusband Peninsula in SE South Australia. The formation of lines of wave formed shelly and pumice rich deposits on, and above the backshore is described. The deposits are buried by dune development, but then later exhumed by aeolian deflation as deflation plains and basins evolve. Aeolian erosion of the finer sandy sediments leads to the creation of a ridge form, herein termed a deflation ridge. A new schematic model of ridge formation is also detailed whereby deflation ridges are formed by the aeolian erosion and deflation of shell or pumice concentrations and lag deposits.

Calibrating Holocene human–environment interactions using ancient narratives: The example of Ngurunderi in South Australia

The essence of stories of human–environment interactions can be preserved in oral contexts for millennia, creating novel opportunities for humanizing the past. This study examines stories (knowledge-rich narratives) about the ancestral being Ngurunderi, told by Ngarrindjeri peoples of South Australia. Three elements of the Ngurunderi narrative are considered. The first recalls his journey along a 170-km long coastal barrier (Younghusband Peninsula) when this was continuous. The second discusses Ngurunderi’s encounters with what are now islands off the Fleurieu Peninsula, some of which he created, interpreted as memories of when sea level was lower and “islands” were contiguous with the mainland. The third refers to the crossing of a land connection between modern Kangaroo Island and the Fleurieu Peninsula, later submerged to form Backstairs Passage. Using paleogeographic data, the most recent times at which each narrative element could have taken place and observed by people are estimated. This research suggests that: (1) stories about Younghusband Peninsula may be >6700 years cal BP; (2) islands off the Fleurieu Peninsula were created 6800–10,400 cal BP; and (3) submergence of Backstairs Passage occurred 11,000–10,100 cal BP. Narratives are linked to the period of early Holocene sea-level rise, the rapid 8200-cal BP sea-level rise event, and stabilization of sea level 7000–6000 cal BP. These narratives humanize the past and provide information that can be interpreted as both observed coastal and seascape changes as well as past human responses to rising sea level that can inform our future encounters with coastal-landscape change.

Coastal transgressive dunefield evolution as a response to multi-decadal shoreline erosion

The Younghusband Peninsula coastal barrier extends ∼190 km and is predominantly comprised of a mix of active, semi-stabilised and stabilised (relict) transgressive and parabolic dunefields. Wave driven shoreline erosion has triggered the rapid development of a transgressive dunefield along a portion the peninsula. This study focuses on a ∼2 km region with the highest regional erosion rates (> −2.0 m/year since 1988), and which has experienced rapid destabilisation and subsequent landward translation of the dunefield. Aerial LIDAR derived datasets of the barrier system from 2008 and 2018 and eight drone photogrammetry surveys between August 2020 and April 2022 are used to compare the rates of change across the beach-dune system. The net and intra-survey changes are used to show the short- to medium-term system response and illustrate the relationship of sediment dynamics to the developing morphology and structure of the dunefield. Shoreline change rates (m/yr) are sourced from the Digital Earth Australia coastlines dataset which provides annual rates for continental Australia from a Landsat time series (1988–2021). When the rate of shoreline change is segmented from the total dataset to the study time-period (2008–2021), the average resulting rates show an increase from −2.2 m/yr to −3.3 m/yr, respectively. This coincides with a landward advance rate of >10 m/yr from 2008 of the dunefield edge, with the fastest eroding dune toes corresponding to regions with the highest rate of dunefield translation and transgression. Net volumetric totals and their ratios of gain to loss of sediments show that significant sediment is lost to offshore during the retrogradation of the dunefield as only a fraction of the stoss slope sediment is transferred landwards. All regions of the dunefield exhibit a net loss of sediments but the high-temporal resolution shows that the magnitude of 3D changes varies through time. An adapted model of erosional stoss slope evolution and dunefield development is advanced and a temporal model of transgressive dunefield evolution is synthesised.

Ground Penetrating Radar of Paleoblowouts and Transgressive Dunes, Younghusband Peninsula, South Australia

Warner, A.L.; Hesp, P.A.; Keane, R., and Gontz, A.M., 2022. Ground penetrating radar of paleoblowouts and transgressive dunes, Younghusband Peninsula, South Australia. Journal of Coastal Research, 38(5), 885–895. Coconut Creek (Florida), ISSN 0749-0208. Ground penetrating radar (GPR) can be used to elucidate the spatial and temporal relationships of paleoshorelines and dunefield evolution and aid in understanding past landscapes in order to help predict future evolutionary pathways of barrier development. GPR was used on the Younghusband Peninsula coast of Southern Australia at a location known as 42 Mile Crossing. The barrier is on the longest beach in Australia and hosts a Holocene transgressive dunefield system. The site also contains many active, modern, and stabilized blowouts. This study aimed to image buried (paleo) blowouts, analyze the subsurface strata of the area, and attempt to relate these findings to the past transgressive dunefield processes, phases, and architecture. The study was able to characterize the buried blowout's shape, size, and dominant wind direction, and the site's stratigraphic evolution.

Review and direct evidence of transgressive aeolian sand sheet and dunefield initiation

AbstractThe multiple hypotheses which exist to explain the initiation of transgressive aeolian sand sheets and dunefields, are reviewed and discussed. Direct evidence supporting many of these hypotheses is largely lacking. In South Australia, the Younghusband Peninsula coastal barrier extends ~180 km and predominantly comprises transgressive and parabolic dunefields. The 42 Mile Crossing area on the barrier is undergoing significant erosion at variable rates of 0.5 to 5.0 m/yr, and a new transgressive aeolian sand sheet has rapidly developed in ~1 year and is extending landwards at an average rate of 13 m/yr. This research provides unequivocal evidence that large‐scale shoreline and dunefield erosion does lead to the development of a new transgressive aeolian sand sheet (and eventual dunefield) phase thereby demonstrating an initiation mechanism that is likely linked to future sea level rise and climate change. We also show that the initiation process, and, in particular, the subsequent rate of sand sheet transgression occurs at an incredibly rapid rate (+100 m in 8 years).Plain Language SummaryCoastal sand dunes border many of the world's coastlines and are highly adapted to local climate and conditions. How coastal dunes transition from predominantly vegetated and stable systems to wind‐blown sand sheets and dunefields transgressing prior terrain is a research area of pressing relevance due to forecasts of sea level rise and climate change. The factors or triggers that are considered to initiate transgressive aeolian sand sheets and dunefields are reviewed. The formation and evolution of a new transgressive aeolian sand sheet phase triggered by large‐scale shoreline erosion in South Australia is presented. According to the results from historical and satellite images, local shoreline erosion began in the late 1970s and has continued at highly variable rates. We show that once the foredune was removed, the high scarp created by wave erosion of the relict, vegetated transgressive dunefield destabilized and was then eroded by wind processes leading to the rapid development of a transgressive aeolian sand sheet. The initiation and evolution of the sand sheet provides an excellent example of how dunefields might respond to future sea level rise and climate change.

Surfzone-beach-dune interactions along a variable low wave energy dissipative beach

The different possible factors that influence or drive the observed volumetric and morphological variation in foredunes located along 16 km of a low wave energy, dissipative southern section of the 190 km long Younghusband Peninsula (South Australia) are examined. Grain size, wind energy, coastline orientation, and vegetation species presence/absence vary only slightly along this coast providing a unique site to study other drivers of coastal change. Results show that foredune height and volume progressively increase towards the north coincident with a gradual increase in wave energy. A significant correlation between foredune volume and wave energy is established, while no apparent relationship with other controlling factors was found, confirming the importance of wave energy in the dune building process on wave-dominated beaches. Results indicate that (1) all other factors being equal, wave energy can drive the morphological evolution of foredunes; (2) minor changes in wave energy can result in differences in the long-term beach and dune sediment budget; and, (3) the surfzone-beach-dune interactions model is applicable to coasts with small scale gradients in wave energy.

Effects of the Increase in Vegetation Cover and Impact of Rabbits on the Geomorphology of Parabolic Dunes (Younghusband Peninsula - SA, Australia)

Effects of the Increase in Vegetation Cover and Impact of Rabbits on the Geomorphology of Parabolic Dunes (Younghusband Peninsula - SA, Australia)

Geochronology and evolution of a complex barrier, Younghusband Peninsula, South Australia

This study examines the southeastern end of the Younghusband Peninsula in South Australia at a location called The Granites in order to gain a better understanding of the processes of formation of the foredune ridge system, and to investigate the drivers that controlled its progradational development during the Holocene. Our findings are based on a morphological analysis, a ground penetrating radar survey, and 14C and OSL dating. The Younghusband Peninsula at The Granites was formed by an initial aggradational phase resulting in a single complex foredune ridge, and which ended around 4.3 ka, and by a regressive (progradational) barrier phase (750 m wide) that developed in the last 4.3 ka, under very low rates of progradation (0.38 to 0.09 m/yr). The last part of this phase shows significant foredune ridge building in the last 1000 years or so. Barrier progradation via foredune ridge development is likely an effect driven by low wave energy that favored conditions for coastal stability and foredune formation. Paleontological and GPR data indicate a maximum sea-level of +1.23 to +1.5 m, respectively, during initial barrier development. The foredune ridge plain of the barrier experienced at least three phases of significant aeolian activity with ages centered at around 3.9, 3.4 and 3.0 ka suggesting their occurrence at 500 to 400-year events. Computer modelling indicates that sediments for the progradational phase of the barrier were provided by the forced regression produced by a sea-level fall over the past 4.3 ka. The large foredune complex formed during the last phase of progradation could be the result of both the very low progradation rate of 0.09 m/yr, and periods of disturbance possibly related to enhanced storm activity.

Geological field guides as educational tools: the Coorong, South Australia

The South Australian (SA) Division of the Geological Society of Australia (GSAust) has a working subcommittee responsible for preparation of geological field guides. The target audience for these guides comprises persons who have an interest in natural environments, but who do not necessarily have specialist education in the Earth sciences. Care is taken to avoid excessive and unnecessary use of jargon, but where required, technical terms are used with appropriate explanations; ‘dumbing down’ is avoided and suitable references are cited for those who seek further information. Field guides can be downloaded from the GSAust web site. Later editions may be updated for mobile devices. The over-arching aim of the subcommittee is to contribute to public education. The Coorong is a back-barrier coastal lagoon that, together with Lake Alexandrina and Lake Albert, constitute the modern estuary of the River Murray. The Younghusband Peninsula is a Holocene beach-dune barrier that was formed as the rising postglacial sea transported sandy sediment shoreward from the exposed Lacepede Shelf. The peninsula stabilised following culmination of the postglacial marine transgression, at the same time isolating a narrow back-barrier lagoon, the Coorong, from the direct impact of the Southern Ocean. The Coorong is a landscape icon rated highly as a tourist attraction. It has importance for ornithologists and other scientists (including geologists) and is the ancestral home of the Ngarrindjeri people. There is a diverse group of people who might be interested in a well-presented and authoritative field guide to this area. The Coorong and associated features thus provide a landscape that underpins consideration of two major concepts: Earth’s global climate has greatly varied during the Pleistocene; glacial and interglacial climatic events have been widely identified within a consistent chronologic framework; and the present global climate is interglacial. Sea-level is lower during cooler glacial times when increased amounts of water are stored as ice on land, particularly in the polar and highland (alpine) regions; sea-level rises during warmer interglacial times when meltwater from glaciers and ice sheets flows into the oceans; and in the present warm-interglacial climate sea-level is high.

Changes in vegetation cover on the Younghusband Peninsula transgressive dunefields (Australia) 1949–2017

AbstractStudies have shown that the impact of climate change, human and animal actions on coastal vegetation can turn stabilized dunes into active mobile dunes and vice versa. Yet, the driving factors that trigger vegetation changes in coastal dunes are still not fully understood. In the transgressive dunefields of the Younghusband Peninsula (south‐east coast of South Australia) historical aerial photographs show an increase in vegetation cover over the last ~70 years. This study attempts to identify the causes of the changes in vegetation cover (1949 to 2017) observed in a typical section of the coastal dune systems of the Peninsula. Vegetation cover was first estimated for various years using the available historical aerial photography (long‐term changes – 1949 to 2017) and recent satellite imagery (short‐term annual changes – 2010 to 2017) for the area, and then results were discussed against the observed changes in climatic variables and rabbit density, factors that could have played a role in this transformation. Results of long‐term changes show that the vegetation cover has increased significantly from 1949 to 2017, from less than 7% vegetation cover to almost 40%, increasing dune stabilization and forming parabolic dune systems. Periods with the largest growth in vegetation cover (1952‐1956 and 2009‐2013) coincide with a significant decline in rabbit numbers. Rabbit density was found to be the primary factor linked to the rapid vegetation growth and stabilization of the dunefield, for both decadal long‐term (last 68 years) and annual short‐term changes (last 8 years). Other factors such as changes in rainfall, aeolian sediment transport, land use practices, and the introduction of invasive plants have apparently played a limited to negligible role in this stabilization process. © 2018 John Wiley & Sons, Ltd.

Marine and estuarine phylogeography of the coasts of south-eastern Australia

Understanding a region’s phylogeography is essential for an evolutionary perspective on its biological conservation. This review examines the phylogeographic structures in south-eastern Australia that have been revealed by mitochondrial DNA sequencing and other genetic techniques and examines whether they can be explained by known factors. The review covers species that occur in the intertidal zone or, even infrequently, in the shallow subtidal zone. The coasts most frequently associated with phylogeographic structure are the boundaries between the Peronian and Maugean biogeographical provinces in southern New South Wales and the Maugean and Flindersian provinces in South Australia, the areas in Victoria and north-eastern Tasmania separated by the Bassian Isthmus at glacial maxima, long sandy stretches without rocky intertidal habitat on the Ninety Mile Beach in Victoria and the Younghusband Peninsula–Coorong in South Australia, southern Tasmania and Bass Strait, which acts as a barrier for littoral species.

Microfossil evidence for salinity events in the Holocene Coorong Lagoon, South Australia

Nearly 6 m of uncompacted muddy sediment was recovered from the floor of the northern Coorong Lagoon in the core Coorong #5. Radiocarbon analyses of molluscan shells indicate that sedimentation at the core site commenced before 6830 ± 90 yr cal BP, and the presence of Pinus pollen confirms a modern age for the uppermost 0.5 m. Microfossils extracted from the core sediment samples, 2 cm slices at 10 cm intervals, included the foraminifera Ammonia sp., Elphidium excavatum and Elphidium gunteri; the ostracods Osticythere baragwanathi and Leptocythere lacustris; and charophyte oogonia. Shell fragments of the estuarine bivalve Spisula (Notospisula) trigonella in the lowermost 0.7 m of the core are evidence that these sediments were subject to some marine influence, but the absence of foraminifera and ostracods from this same interval indicates that at the core site salinity was not sufficient to support populations of these organisms. Thus, prior to 6830 ± 90 yr cal BP the Younghusband Peninsula was in place, in part isolating the northern lagoon from the Southern Ocean. The initial recorded salinity event is signified by abundant Ammonia sp. at a core depth of 5.2 m. The duration of this event was relatively brief; foraminifera were mostly absent in the immediately overlying 2 m, representing ca 700 yr of sedimentation. This observation is attributed to substantial inflow of freshwater from the River Murray. In the upper 3.0 m, Ammonia sp. was present in most core samples indicating that for most of the past 6000 years the Coorong Lagoon has been sufficiently saline to support a continuing population of this species. At a core depth of 1.3 m, the sediment sample yielded >2000 tests of Ammonia sp., and they were accompanied by maximum pre-modern numbers of E. excavatum, O. baragwanathi and oogonia. Taken together, these data signify the maximum pre-modern salinity event recorded in the core sediments, probably correlating in time with regional drought conditions at ca 3500 yr BP. Elphidium gunteri is confined to the modern sediments where it is abundant and accompanied by equally large numbers of Ammonia sp., E. excavatum, O. baragwanathi and L. lacustris. These data collectively indicate water conditions that are significantly changed from those that prevailed in the Coorong Lagoon for most of the Holocene.

Interstadial age (MIS5c) beach-dune barrier deposits in the Coorong Lagoon, South Australia

Geomorphic inference of interstadial MIS5c sediments within the South Australian Coorong Lagoon is supported by the presence of a linear array of islands and other features, comprising aeolianite and calcrete, lying between and parallel with the Holocene Younghusband Peninsula and the Last Interglacial Woakwine Range coastal barrier complexes. A single published thermoluminescence age of 95 ± 6 ka provides numerical evidence consistent with this interpretation. The difference in altitude between the inferred MIS5c beach-dune barrier and that of the Last Interglacial MIS5e might signify an equivalent difference in the paleo-sea-levels for those times.

The Impact of Exotic Dune Grass Species on Foredune Development in Australia and New Zealand: a case study of Ammophila arenaria and Thinopyrum junceiforme

Marram grass (Ammophila arenaria) and sea-wheat grass (Thinopyrum junceiforme) have been introduced to Australia and New Zealand. This study examines the morphology of incipient foredunes and established foredunes associated with these species at two sites, Mason Bay in southern New Zealand, and the Younghusband Peninsula in South Australia. Both species invaded the existing foredunes very rapidly. In both cases the antecedent topography comprised relatively sparsely vegetated, irregular foredunes. Invasion resulted in continuous, regular, evenly vegetated foredunes. At Mason Bay a massive foredune has formed since 1958, in conjunction with Ammophila. Thinopyrum has formed an incipient foredune, with a ramp or terrace morphology, along the Younghusband Peninsula, South Australia. In both cases gaps in the former foredune have been closed and the indigenous foredune vegetation has been displaced. Both species may decrease the frequency and severity of blowout development. They are likely to be resilient to aeolian processes of sedimentation compared with dunes formed by indigenous species. Ammophila survives burial, is tolerant of drought and is resistant to erosion associated with storm surge and high waves. Thinopyrum is very tolerant of salinity. These species may adversely affect the long-term development of coastal barriers by inhibiting transgressive dune development.

Rapid coastal geomorphic change in the River Murray Estuary of Australia

Abstract The River Murray Estuary, a Ramsar Wetland Site, has experienced considerable rapid coastal change during the Quaternary. The interplay of aeolian processes, river flows, tidal oscillations, wave action and variations in relative sea-level due to global sea-level changes and land subsidence, provides the energy for the ongoing dynamism, often accelerated by human impacts. The estuary is the terminus of the Murray-Darling catchment, which covers 1.073 million km 2 of the Australian continent. Terminal Lakes Alexandrina, Albert and the Coorong Lagoon are Holocene features, occupying tectonically subsiding Quaternary interdune areas. They formed in response to eustatic sea-level rise following the Last Glacial Maximum (ca. 20 ka). The last interglacial shoreline (125,000 yr BP) parallels the modern shoreline several kilometres inland. Dislocation of the last interglacial shoreline demonstrates ongoing tectonic subsidence, as does historical seismic activity. The northern half of Hindmarsh Island formed during last interglacial times when it was the sink for dominant longshore transport from the southeast, which pushed the River Murray westward, partly explaining the large bend in the River Murray at Goolwa. The modern coastal barriers of Sir Richard Peninsula and Younghusband Peninsula formed from 7000 yr ago, following glacier melt and sea-level rise. Subsequently, the barriers have migrated landward, sporadically exposing lagoonal sediments on the ocean beaches. Differential loading of the soft lagoonal sediments by advancing dunes, possibly in conjunction with seismic events, has deformed and elevated them to up to 10 m above present sea-level (APSL). During the mid-Holocene an extensive sand flat, with associated dunes, formed immediately inland of the coastal barrier. At least six generations of Late Pleistocene dune systems occur in the region. For example, during last glacial times the climate was drier, colder and windier than at present and a system of parallel, west–east trending, yellow–red desert dunes developed around the lakes. Aeolian processes remain important with occasionally up to 5000 tonnes of sand being in motion along 10 km of the modern shoreline. During mouth migration, dunes up to 2 m high have been formed and vegetated in 12 months, directly inland from the mouth, and replicating the formation of older dunes on Hindmarsh Island. Elsewhere sand blown directly from the barrier system infills channels. Barrage construction on the beach facies of the last interglacial shoreline transformed the estuary into freshwater lakes with permanently raised water levels and reduced the tidal prism by 90%. Increased deposition, upstream and downstream, accompanied barrage construction, as have accelerated lakeshore erosion and the growth and consolidation of the flood tidal delta (Bird Island). These human accelerated changes provide rapidly formed analogues of older Quaternary features, and aid their interpretation. The shape and location of the Murray Mouth is constantly changing, migrating over 1.6 km since the 1830s. Migrations of up to 6 km over the past 3000 yr have influenced sedimentation on the landward shore of the back-barrier lagoonal system.

The impact of past and present land use on a major coastal barrier system

This paper considers the relative impacts of past and present land use on the stability of the major coastal barrier complex of the Younghusband Peninsula and Coorong lake chain of South Australia. Data have been obtained from field survey and mapping, field studies of soil shear strength, interviews, aerial photographs, archaeological survey, documentary and cartographic historical sources. The investigation shows that large-scale changes in dune stability have occurred in the prehistoric past, probably as a result of as yet unspecified climatological/ oceanographic fluctuations. The legacy of both pre-European aboriginal land-firing and of European pastoralism appears to have had a minor impact on the dunes compared to the more recent use of off-road recreational vehicles. Even in the most intensively used areas, however, local stability of the sand dunes occurs, apparently due to the exposure of prehistoric shell-middens interbedded with palaeosols, which together offer greater resistance to off-road vehicles than many other soils in the barrier system. There are important differences in the scale and type of geomorphic impact of the many kinds of vehicles now taken off-road, and in the attitudes of different users of the same type of vehicle. These attitudes and impacts interact with each other, and with various aspects of the physical geography of the region, to cause the pattern and rate of environmental degradation to spread in a characteristic manner. In particular, the character and distribution of scrub, mallee and lacustrine habitats, as well as of settlements, are shown to markedly affect the manner in which the entire network of tracks and used ground develops. The pattern of past and present access and communications routes seems to have been particularly important. For management purposes it is important to view these interactions not only at the level of the individual track or path, but also at the level of the entire National Park based on the coastal barrier system, and then to expand the management framework again to regional level at which the off-road vehicle problem must ultimately be resolved. These observations are incorporated into suggestions for improving the control of off-road recreational vehicle use in the barrier system, and in the region at large.