Abstract for the 18th NSW Coastal Conference

The historical record reveals that at least five tsunamis have impacted the Western Australian coast (1993, 1977, 1994, 2004, 2006). We document the geomorphic effects of these tsunamis through field investigations, analysis of pre and post-tsunami satellite imagery, collation of historical reports and recording of eyewitness accounts. The tsunamis had flow depths of less than 3 m, inundation distances of up to several hundred metres and a maximum recorded run-up height of 8 m a.s.l. Geomorphic effects include off-shore and near-shore erosion and extensive vegetation damage. In some cases, vegetated foredunes were severely depleted or completely removed. Gullies and scour pockets up to 1.5 m deep were eroded into topographic highs during tsunami outflow. Eroded sediments were redeposited landward as sediment sheets several centimetres thick. Isolated coral blocks and oyster-encrusted boulders were deposited over coastal dunes. However, boulder ridges were often unaffected by tsunami flow. The extent of inundation from the most recent tsunamis can be distinguished as strandlines of coral rubble and rafted vegetation. It is likely taht these features are ephemeral and seasonal coastal processes will obscure all traces of these signatures within years to decades. Recently reported evidence for Holocene palaeotsunamis on the Western Australian coast suggests significantly larger run-up and inundation than observed in the historical record. The evidence includes signatures such as chevrons dunes that have not been observed to form during historical events. We have compared the geomorphic effects of historical tsunami with reported palaeotsunami evidence from Coral Bay, Cape Range Peninsula and Port Samson. We conclude that much of the postulated palaeotsunami evidence can be explained by more common and ongoing geomorphic processes such as reef evolution, aeolian dune development and archaeological site formation.

The Lower Darling Valley (LDV) Cenozoic sequence contains Paleogene and Neogene shallow marine and shoreline as well as fluvial and shoreline sediments overlain by Quaternary lacustrine, aeolian and fluvial units. Recent investigations in the LDV using multiple datasets have provided new insights into the nature of post-Blanchetown Clay Quaternary fluvial deposition which differs to the Mallee and Riverine Plain regions elsewhere in the Murray Basin. In the LDV Quaternary fluvial sequence, multiple scroll-plain tracts are incised into higher, older and more featureless floodplain terrain. Prior to this study, these were respectively correlated to the Coonambidgal and Shepparton Formations of the Riverine Plain in the eastern Murray Basin. These formations were originally associated with the subsequently discarded Prior Stream/Ancestral River chronosequence of different climatically controlled depositional styles. In contrast to that suggestion, we ascribe all LDV Quaternary fluvial deposition to lateral-migration depositional phases of one style, though with variable stream discharges and channel and meander-scroll dimensions. Successively higher overbank-mud deposition through time obscures scroll traces and provides the main ongoing morphologic difference. A new morphostratigraphic unit, the Menindee Formation, refers to mostly older and higher floodplain sediments, where scroll traces are obscured by overbank mud which continues to be deposited by the highest modern floods. Younger inset scroll-plain tracts, with visible scroll-plain traces, are still referred to as the Coonambidgal Formation. Another new stratigraphic unit, the Willotia beds, refers to even older fluvial sediments, now above modern floodplain levels and mostly covered by aeolian sediments.

Faults of the Lapstone Structural Complex (LSC) underlie 100 km, and perhaps as much as 160 km, of the eastern range front of the Blue Mountains, west of Sydney. More than a dozen major faults and monoclinal flexures have been mapped along its extent. The Lapstone Monocline is the most prominent of the flexures, and accounts for more than three quarters of the deformation across the complex at its northern end. Opinion varies as to whether recent tectonism, or erosional exhumation of a pre-existing structure, better accounts for the deeply dissected Blue Mountains plateau that we see today. Geomorphic features such as the abandoned meanders at Thirlmere Lakes illustrate the antiquity of the landscape and favour an erosional exhumation model. According to this model, over-steepened reaches developed in easterly flowing streams at the Lapstone Monocline when down-cutting through shale reached more resistant sandstone on the western side of the LSC. These over-steepened reaches drove headward (westerly) knick point retreat, ultimately dissecting the plateau. However, a series of swamps and lakes occurring where small easterly flowing streams cross the westernmost faults of the LSC, coupled with over-steepened reaches 'pinned' to the fault zones in nearby larger streams, imply that tectonism plays a continuing role in the development of this landscape. We present preliminary results from an ongoing investigation of Mountain Lagoon, a small fault-bound basin bordering the Kurrajong Fault in the northern part of the LSC.

Geomorphic landscape features and associated surface materials are fundamental to groundwater recharge processes as they form the first layer through which surface water passes before it becomes groundwater. Different surface materials exhibit different water-holding capacity and hence permeability characteristics. In the Broken Hill Managed Aquifer Recharge project, surface-materials mapping in conjunction with geomorphic mapping, has assisted hydrogeological investigations, including recharge predictions, salinity hazard and the identification of potential infiltration basins. Prior to landform identification, LiDAR DEM data was levelled using trend surfaces to eliminate regional slope (~20m). As a consequence of this, an ArcGIS interactive contour tool could be used to identify specific breaks in elevation associated with landform features. Multivariate image analysis of elevation, high resolution SPOT and Landsat-derived wetness further enhanced the contrast between geomorphic elements to confirm mapping boundaries. While specific landforms can be characterised by particular surface materials, these sediments can vary within a single geomorphic feature. Consequently, SPOT multispectral satellite imagery was used to identify surface materials using principal component analysis and unsupervised classification. This approach generated 20 classes; each assigned a preliminary cover/landform attribute using SPOT imagery. Field data (surface and borehole sample, and observations at shallow pits) were used to refine the classification approach. Interactive mapping using a de-trended DEM provided a rapid, effective and accurate alternative to time consuming manual landform digitisation. The combination of these two new products - surface-materials and geomorphic maps - has assisted in the identification of potential recharge sites and naturally occurring infiltration sites.

Dense coral-sponge communities on the upper continental slope (570 - 950 m) off George V Land, east Antarctica have been identified as Vulnerable Marine Ecosystems. We propose three main factors governing their distribution on this margin: 1) their depth in relation to iceberg scouring; 2) the flow of organic-rich bottom waters; and 3) their location at the head of shelf cutting canyons. Icebergs scour to 500 m in this region and the lack of such disturbance is a likely factor allowing the growth of rich benthic ecosystems. In addition, the richest communities are found in the heads of canyons which receive descending plumes of Antarctic Bottom Water formed on the George V shelf, which could entrain abundant food for the benthos. The canyons harbouring rich benthos are also those that cut the shelf break. Such canyons are known sites of high productivity in other areas due to strong current flow and increased mixing with shelf waters, and the abrupt, complex topography.

The World Summit on Sustainable Development implementation plan requires, by 2012, a representative system of marine protected areas (RSMPA) for the purposes of long-term conservation of marine biodiversity. A great challenge for meeting this goal, particularly in data-poor regions, is to avoid inadvertant failure while giving science the time and resources to provide better knowledge. A staged process is needed for identifying areas in data-poor regions that would enable the objectives to be achieved in the long term. We elaborate a procedure that would satisfy the first stage of identifying a RSMPA, including areas suitable as climate change refugia and as reference areas for monitoring change without direct interference of human activities. The procedure is based on the principles of systematic conservation planning. The first step involves the identification of ecologically-separated provinces along with the physical heterogeneity of habitats within those provinces. Ecological theory is then used to identify the scale and placement of MPAs, aiming to be the minimum spatial requirements that would satisfy the principles for a representative system: comprehensiveness, adequacy and representativeness (CAR). We apply the procedure to eastern Antarctica, a region with spatially-restricted sampling of most biota. We use widely available satellite and model data to identify a number of large areas that are likely to encompass important areas for inclusion in a RSMPA. Three large areas are identified for their pelagic and benthic values as well as their suitability as climate change refugia and reference areas. Four other areas are identified specifically for their benthic values. These areas would need to be managed to maintain these values but we would expect them to be refined over time as more knowledge becomes available on the specific location and spatial extent of those values.

The Ord is one of the largest rivers in northern Australia and is located in the Kimberley region of Western Australia. In this study we show that the lower Ord landscape near Kununurra in Western Australia consists of a large scale ancient landscape, possibly pre-Cambrian, being exhumed from beneath flat-lying Cambrian to Carboniferous cover rocks. Additional post-Permian landscapes are being formed by this process. The Ord Valley alluvium is of late Pleistocene to Holocene in age and consts off upward fining gravels, sands and clays infilling an inset valley profile. The Ord River initially flowed to the sea via the keep River estuary, however a major avulsion, possibly due to sedimentatain topping a low point in the surrounding valley walls, occurred possibly as recently as 1,800 years ago. As a result to mouth of the Ord shifted some 100 km to the east, to Cambridge Gulf, its course through the former alluvial plain and along the new course across the coastal plain was incised, and a scabland formed across the low point of Tararar Bar. This association of very ancient (pre-Paleozoic) landscape elements and by thin, very young weathering profiles and young sedimentary accumulations in alluvial valleys is paradoxical in the broader Australian pattern where very ancient landscape elements are associated with ancient sedimentary infill and weathering profiles.

The Queen Charlotte Fault (QCF) off western Canada is the northern equivalent to the San Andreas Pacific - America boundary. Geomorphology and surface processes associated with the QCF system have been revealed in unprecedented detail by recent seabed mapping surveys. The QCF bisects the continental shelf of British Columbia forming a fault-valley that is visible in multibeam sonar bathymetry data. The occurrence of the fault within a valley, and its association with what appear to be graben structures, suggest the fault may exhibit minor rifting (extension) as well as strike-slip motions in the region offshore from Haida Gwaii (Queen Charlotte Islands). Fault-valley formation, slumping and stranding of submarine canyon thalwegs are geomorphic expressions of QCF tectonism, illustrating the general applications of multibeam technology to marine geophysical research.

On 23 March 2012, at 09:25 GMT, a MW 5.4 earthquake occurred in the eastern Musgrave Ranges region of north-central South Australia, near the community of Ernabella (Pukatja). Several small communities in this remote part of central Australia reported the tremor, but there were no reports of injury or significant damage. This was the largest earthquake to be recorded on mainland Australia for the past 15 years and resulted in the formation of a 1.6 km-long surface deformation zone comprising reverse fault scarps with a maximum vertical displacement of over 0.5 m, extensive ground cracking, and numerous rock falls. The maximum ground-shaking is estimated to have been in the order of MMI VI. The earthquake occurred in non-extended Stable Continental Region (SCR) cratonic crust, over 1900 km from the nearest plate boundary. Fewer than fifteen historic earthquakes worldwide are documented to have produced co-seismic surface deformation (i.e. faulting or folding) in the SCR setting. The record of surface deformation relating to the Ernabella earthquake therefore provides an important constraint on models relating surface rupture length to earthquake magnitude. Such models may be employed to better interpret Australia's rich prehistoric record of seismicity, and contribute to improved estimates of seismic hazard.