Chris Gouramanis

Holocene lake-level fluctuations in Lakes Keilambete and Gnotuk, southwestern Victoria, Australia

Reconstructed Holocene lake-level curves from two saline, hydrologically closed maar crater lakes in southwestern Victoria, Australia, show near synchronous lake-level changes throughout the Holocene. We show that lake levels, reconstructed from sediment particle size and ostracod valve chemistry (δ18O and Sr/Ca) have undergone rapid (<100 yr), large (>10 m) fluctuations throughout the Holocene. Finer sampling resolution shows a more sensitive response to Holocene climate than was previously presented for Lake Keilambete. Both maar crater lakes show a short-lived maximum in Holocene lake levels around 7.2 ka. The period of lake filling leading to peak lake levels matches the phase of most effective precipitation (7.4–7.0 ka) reconstructed from a high-resolution speleothem record from northern Tasmania. Water levels declined in both lakes during the mid Holocene, with a more substantive decline after ~5 ka which coincides with the end of the Southern Hemisphere hypsithermal. Water levels continued to oscillate with a periodicity of around 300–700 years, before reaching a late-Holocene nadir around 1.8 ka (Keilambete) and 1.3 ka (Gnotuk). The trend and periodicity of oscillations in the maar water levels show commonalities to δD in the Dome C ice core, and suggest that temperature may be a significant component in influencing the Precipitation/Evaporation (P/E) ratio in southeastern Australia during the Holocene.

Integrating different records to assess coastal hazards at multi-century timescales

ABSTRACT Switzer, A.D., Yu, F., Gouramanis, C, Soria, J, Pham, T.D. 2014. An integrated approach to assessing coastal hazards at multi-century timescales. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 723–728, ISSN 0749-0208. In many places on earth, the written record of coastal flooding events from tropical cyclones (typhoons, hurricanes) and tsunamis is too short or inconsistent to accurately assess the hazard posed by both kinds of event on scales beyond those of the average human lifespan. In this paper we summarize an integrated research paradigm that incorporates instrumental, historical, archaeological and geological records to extend the record of coastal flooding events to generate a multi-century analysis of recurrence interval for coastal flooding, thus, improving long-term risk assessment. The two primary factors in assessing risk from coastal hazards are frequency and magnitude. These can be addressed through field and modeling studies of washover deposits where they are found. We also summarize recent advances in the identification of overwash events from the geological record and report on the progress to distinguish storm and tsunami deposits. The recent advances have increased the utility of tsunami and storm deposits to improve coastal risk assessment.

High-frequency coastal overwash deposits from Phra Thong Island, Thailand

The 26th December 2004 Indian Ocean Tsunami (IOT) emanated from an Mw 9.2 earthquake that generated a 1600 km-long rupture along the Sumatran Megathrust and generated tsunami waves up to 30 m high. The IOT directly impacted the Bay of Bengal and east Africa, with over 283,000 people perishing. At the time, this catastrophic event was considered unprecedented and sparked intense investigations to test this claim. It is now believed that four pre-2004 IOT events have occurred in the last 2500 years, recurring every 550 to 700 years. Much of this information comes from Phra Thong Island, Thailand, where a sequence of four stacked sandsheets separated by organic units has been recognised and compared to the 2004 IOT event. Recently, ground-penetrating radar on Phra Thong Island identified a region that could not be explained by the known stratigraphy. The stratigraphy of the area was investigated from auger cores and pits, and several previously-unrecognised sandsheets were identified and compared to the known tsunami sandsheets. The proximity of the newly-recognised sandsheets to the palaeo-coastline of Phra Thong Island does not preclude the impacts of localised storms in sandsheet emplacement or that tsunamigenic earthquake recurrence may have been more frequent in the past.

Developing a Historical Typhoon Database for the Southeastern Chinese Coastal Provinces, 1951-2010

Many countries have developed their own typhoon database for the use in understanding historical typhoon. However, when each database is compared, inconsistencies are evident in terms of the depth of information provided. This paper outlines the development of a combined database and provides comprehensive details of typhoons impacting the southeastern Chinese coastal provinces of Fujian, Guangdong, Hainan, Hong Kong, Macau, Taiwan and Zhejiang. The database is titled “A historical typhoon database for the southeastern Chinese coastal provinces, 1951-2010” and contains entries for 581 reported typhoon events that have occurred between 1951 and 2010, with standard typhoon information presented where obtainable. Importantly, additional information on the number of casualties is included for 265 typhoon events that have records of the death toll, and 131 events that have records of the economic loss caused by each event. Using this new database, we highlight the worst typhoon events that have impacted the southeastern Chinese coastal provinces in terms of fatalities from 1951 to 2010. A decreasing trend in both the number of fatalities and economic loss are recorded for the entire data period for the former and since 1993 for the latter.

High-resolution, multiproxy palaeoenvironmental changes recorded from Two Mile Lake, southern Western Australia: implications for Ramsar-listed playa sites

Numerous saline playa lakes exist across the arid, semiarid and temperate regions of Australia. These playa lakes exhibit a diverse range of hydrological conditions to which the Australian aquatic invertebrate biota have become adapted and which the biota can utilise as refugia in times of hydrological deterioration. Saline playas also yield palaeoenvironmental records that can be used to infer lacustrine and catchment responses to environmental variability. We present a palaeoenvironmental record recovered from Two Mile Lake, a saline playa from southern Western Australia. Dating, based on quartz optical luminescence and 14C accelerator mass spectrometry of biogenic carbonates and organic fibres, suggests that most of the sediment was rapidly deposited at 4.36 ± 0.25 thousand years ago. Ostracods and non-marine foraminifera preserved in the sediment show periods of faunal colonisation of the lake with oscillations between hypersaline and oligosaline conditions. The geochemistry of ostracod valves and foraminifera tests suggests higher-frequency variability within the lake, and palynological changes indicate landscape changes, possibly in response to fire. The Two Mile Lake record highlights the utility of saline playas as archives of environmental change that can be used to guide wetland health management, particularly under the impacts of a changing climate.

Ground penetrating radar (GPR) survey of formerly mined coastal sand in central Vietnam: a rapid, non-invasive method for investigating the extent and impact of mined areas

 Abstract— Ground Penetrating Radar (GPR) offers a non- invasive, high-resolution subsurface imaging method that can be used to investigate and characterise the sedimentary features and depositional history of various coastal deposits. GPR utilises the electromagnetic wave properties in the megahertz frequency range and can generate 2D and 3D images of the subsurface to identify coastal depositional features to a depth in excess of 20m. In this study we use a series of GPR surveys to identify the depth and physical characteristics of an infilled site formerly subject to sand mining for heavy mineral sands. We outline a fast non- invasive technique that allows large areas of coastal dunes to be imaged for the purposes of delineating past land uses. The technique is likely to be particularly applicable to developing coasts where the historical record is incomplete or fragmentary or there has been a history of poorly constrained or illegal sand mining.

MONITORING COASTLINE CHANGE IN THE RED RIVER DELTA USING REMOTELY SENSED DATA

This study focuses on the use of remotely sensed data for monitoring coastline changes in the Red River Delta during the 1998 to 2008 period. For the satellite image data processing, the shoreline was defined as the mean sea level on the muddy coast where the tide is the dominant dynamic factor and as the mean high sea level on the sandy coast where the ocean waves are the dominant dynamic factor. A GIS approach was used for the quantitative analysis of coastline change. It was observed that the coastline change in the Red River Delta underwent complicated changes during this 10 year period. In this period, the accretion rate in Red River Delta coastal area was about 10,256ha and the erosion rate was about 542ha. In the Hai Hau and Hau Loc coastal areas, erosion occurred in a large scale and was very intense. Along other coastlines of the Red River Delta, sediment accretion dominated at rates of over 30m/year. These zones of varying erosion and accretion have important implications for coastal zone management in the Red River Delta region.