Quantifying Storm Tide Risk in Cairns

The United Nations International Decade for Natural Disaster Reduction (IDNDR)gave rise to an increasing level of attention to the risks posed by a range of naturalhazards and the development of strategies by which to reduce those risks. It waswidely recognised that in order to evaluate risk treatment strategies it was necessaryto `measure' the level of risk that already existed and the level of risk that would beencountered with the treatment strategy(s) in place.This paper outlines the methodology developed under the AGSO (now GeoscienceAustralia) Cities Project to quantify the risk associated with storm tide inundation. It includes the methodology for `measuring' the level of community exposure to storm tide hazards and the methodology for `measuring' community vulnerability. The Far North Queensland city of Cairns is used as the case study to demonstrate the application of these methods.     

Curved scanline theory

This work develops the theory of measuring fracture frequency with curved scanlines, as a direct development of work done by others on straight scanlines. Various possible shapes for curved scanlines range between triangular and rectangular, with circular as a reasonable preliminary selection. The discrepancy among different selections decreases with increasing roughness amplitude of the scanline. Analytic solutions for average fracture frequency are given for circular scanlines through single and multiple fracture sets. Results for single fracture sets are plotted. The analytic solution for the general situation of any shape scanline through multiple fracture sets is given. Analytic solutions are given and plotted for circular scanlines through a fracture fabric ellipsoid. A circular scanline spanning 180 degrees yields a global fracture frequency of statistical significance.     

Overburden deformation associated with halokinesis in the Southern North Sea: implications for the origin of the Silverpit Crater

Gravitational collapse in response to the creation of salt swells and diapirs is a common phenomenon within regions such as the Southern North Sea. Although collapse faulting and slumping of linear salt swell flanks has previously been documented, the existence of concentric collapse structures surrounding diapirs and isolated salt lows is a recently recognised feature. 3-D seismic data from the Southern North Sea demonstrates that concentric collapse faulting around both diapirs and subcircular salt lows is common. The recognition of concentric collapse structures formed in response to salt withdrawal, and adjacent inflation, provides an alternative mechanism for the origin of the proposed Silverpit impact crater.     

Glacial conditions that contribute to the regeneration of Fountain Glacier proglacial icing,Bylot Island,Canada

Proglacial icings are one of the most common forms of extrusive ice found in the Canadian Arctic. However, the icing adjacent to Fountain Glacier, Bylot Island, is unique due to its annual cycle of growth and decay, and perennial existence without involving freezing point depression of water due to chemical characteristics. Its regeneration depends on the availability of subglacial water and on the balance between ice accretion and hydro‐thermal erosion. The storage and conduction of the glacial meltwater involved in the accretion of the icing were analyzed by conducting topographic and ground penetrating radar surveys in addition to the modelling of the subglacial drainage network and the thermal characteristics of the glacier base. The reflection power analysis of the geophysical data shows that some areas of the lower ablation zone have a high accumulation of liquid water, particularly beneath the centre part of the glacier along the main supraglacial stream. A dielectric permittivity model of the glacier – sediment interface suggests that a considerable portion of the glacier is warm based; allowing water to flow through unfrozen subglacial sediments towards the proglacial outwash plain. All these glacier‐related characteristics contribute to the annual regeneration of the proglacial icing and allow for portions of the icing to be perennial. Copyright © 2013 John Wiley & Sons, Ltd.     

Lake sedimentary processes and vegetation changes over the last 45k cal a bp in the uplands of south-eastern Amazonia

This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions.     

Fish,Macroinvertebrate and Epifaunal Communities in Shallow Coastal Lagoons with Varying Seagrass Cover of the Northern Gulf of Mexico

Coastal lagoons are ubiquitous along coastlines worldwide. Here, we compare the abundance of epifauna, seagrass-associated macroinvertebrates, and small fish across a gradient of seagrass cover in shallow coastal lagoons of the northern Gulf of Mexico. Two of the lagoons had little or no seagrass cover (0–18.8 %), and four had high cover (83.8–97.5 %). All of the lagoons were partially covered with fringing marsh. We hypothesized that, due to habitat redundancy between seagrass beds and fringing marshes, seagrass-associated fish and macroinvertebrates would not be largely reduced despite the large differences in seagrass cover among the lagoons. Our results support this hypothesis. For most sampling dates, we did not find significant differences in fish and macroinvertebrate abundance among the lagoons and, when we did, several highly vegetated lagoons did not have larger abundances than sparsely vegetated lagoons. The extreme shallowness of the lagoons studied (<1 m) may also provide further protection from large predatory fishes in the absence of seagrasses. Our results also suggest that marsh detritus, by providing habitat for epifauna and helping maintain prey availability, may further temper reductions in seagrass-associated fishes and macroinvertebrates following seagrass decline. The results highlight the importance of marsh-bordered, shallow lagoons as habitat for small fish and macroinvertebrates regardless of seagrass cover. This study contributes to the characterization of habitat redundancy in coastal ecosystems and pinpoints the importance of considering all habitats in concert for the proper understanding and management of coastal ecosystems.