Implementing low-cost landslide risk reduction: a pilot study in unplanned housing areas of the Caribbean

Landslides pose a serious physical and environmental threat to vulnerable communities living in areas of unplanned housing on steep slopes in the Caribbean. Some of these communities have, in the past, had to be relocated, at costs of millions of dollars, because of major slides triggered by tropical storm rainfall. Even so, evidence shows that: (1) risk reduction is a marginal activity; (2) there has been minimal uptake of hazard maps and vulnerability assessments and (3) there is little on-the-ground delivery of construction for risk reduction. This article directly addresses these issues by developing a low-cost approach to the identification of the potential pore pressure changes that trigger such slides we seek to address these three commentaries directly. A complex 45–60° slope site in St Lucia, West Indies was selected as a pilot for a modelling approach that uses numerical models (FLAC and CHASM) to verify the need for surface water management to effectively reduce landslide risk. Following the model confirmation, a series of drains were designed and constructed at the site. Post-construction evidence indicates the methodology to be sound, in that the site was stable in subsequent 1-in-1 to 1-in-4 year rainfall events. A critical feature of the approach is that it is community-based from data acquisition through to community members participating in construction.     

Microstructural evolution of the Seridó Belt, NE-Brazil: the effect of two tectonic events on development of c-axis preferred orientation in quartz

The polyphase evolution of the Seridó Belt (NE-Brazil) includes D₁ crust formation at 2.3–2.1 Ga, D₂ thrust tectonics at 1.9 Ga and crustal reworking by D₃ strike-slip shear zones at 600 Ma. Microstructural investigations within mylonites associated with D₂ and D₃ events were used to constrain the tectono-thermal evolution of the belt. D₂ shear zones commenced at deeper crustal levels and high amphibolite facies conditions (600–650 °C) through grain boundary migration, subgrain rotation and operation of quartz c-prism slip. Continued shearing and exhumation of the terrain forced the re-equilibration of high-T fabrics and the switching of slip systems from c-prism to positive and negative a-rhombs. During D₃, enhancement of ductility by dissipation of heat that came from syn-D₃ granites developed wide belts of amphibolite facies mylonites. Continued shearing, uplift and cooling of the region induced D₃ shear zones to act in ductile-brittle regimes, marked by fracturing and development of thinner belts of greenschist facies mylonites. During this event, switching from a-prism to a-basal slip indicates a thermal path from 600 to 350 °C. Therefore, microstructures and quartz c-axis fabrics in polydeformed rocks from the Seridó Belt preserve the record of two major events, which includes contrasting deformation mechanisms and thermal paths.     

西天山喇嘛苏铜矿成矿斑岩的岩石学、地球化学特征及成因探讨

位于西天山别珍套-科古琴晚古生代岛弧西段的喇嘛苏铜矿床是区内最大的铜矿床,与成矿作用有着密切关系的斑岩体为英云闪长斑岩、花岗闪长斑岩,是同源岩浆分异演化的产物,且花岗闪长斑岩可能属于岩浆演化晚期的产物。本区成矿斑岩的主量、微量元素和Sr-Nd同位素地球化学特征表明,其富集大离子亲石元素,而相对亏损高场强元素,出现了较为明显的Ta、Nb负异常,初始锶同位素ISr和εNd(t=390Ma)值分别为0.7072～0.7076和-0.32～0.17,显示壳幔混合源的特征,利用Sr和Nd同位素估算其源区物质约有50%来源于地壳。岩石地球化学特征指示了其为典型钙碱性火山弧花岗岩,暗示其形成于大陆弧环境。结合区域地质背景,推测本区成矿斑岩是在洋壳俯冲作用下发生部分熔融,交代原先的地幔楔,并混合了部分下地壳的物质,经历分离结晶作用的产物,其形成可能与晚古生代准噶尔洋板块向南的俯冲作用有关。结合东西天山的成矿斑岩的地球化学特征对比研究,岩浆源区的差别可能导致不同类型斑岩型矿床的形成,斑岩型铜矿床的形成较斑岩型钼矿床可能有更少的地壳物质贡献。     

Desert knowledge: integrating knowledge and development in arid and semi-arid drylands

Globalisation presents particular challenges for deserts given that their sparse populations, which are amongst the world’s poorest in an absolute economic sense, tend to be remote from major markets and have only a distant, marginal voice in political and policy decision making. Here we are defining deserts as the arid and semi-arid drylands that encompass 70% of Australia and 25% of the world’s land surfaces. The value of the knowledge that local traditions and science have generated about living sustainably in deserts is being promoted and extended through the ‘desert knowledge’ movement in Australia. The Australian research reported here, together with a contribution from Niger that offers a contrast and some lessons for Australia, is largely underpinned by a neopopulist paradigm of development stressing respect for local knowledge, participatory practice and empowerment. Research in partnership with desert Aboriginal groups is contributing to their engagement with new livelihood opportunities. The local knowledge of livestock graziers is also being engaged to support sustainable management of desert water sources and landscapes for multiple values. The research reported here also addresses opportunities and challenges for local norms, identities, knowledge systems, governance and livelihoods from broader scale processes and institutions. In doing so it contributes to a ‘neo-ideographic approach’ wherein desert people might better harness their locality, knowledge and diversity in adaptations that shape their encounters with globalisation. It also points to considerable scope to mature such an approach.     

Relationships between molecular bacterial diversity and chemistry of groundwater in the Wairarapa Valley,New Zealand

Groundwater plays an important role in New Zealand water supplies and hence monitoring activities are conducted regularly. Most monitoring programmes aim to evaluate groundwater chemistry and almost completely overlook the microbial component in this ecosystem. In our present study, the bacterial community structure of groundwater in the Wairarapa Valley was examined using the terminal restriction fragment length polymorphism (T-RFLP), and relationships between bacterial community structure and groundwater chemistry, aquifer confinement and groundwater usage were explored. In addition, the results from this study were compared with a previous T-RFLP survey of the same area in an attempt to detect changes in bacterial community structure over time. The data obtained suggested that bacterial community structure was related to groundwater chemistry, especially to redox conditions. Species composition showed minimal variation over time if groundwater chemistry remained unchanged. These findings reflect the potential of using bacterial communities as biological indicators to evaluate the health of groundwater ecosystems. We suggest that it is important to include this type of broad bacterial diversity assessment criteria into regular groundwater monitoring activities.     

An integrated approach for evaluating the effectiveness of landslide risk reduction in unplanned communities in the Caribbean

Despite the recognition of the need for mitigation approaches to landslide risk in developing countries, the delivery of ‘on-the-ground’ measures is rarely undertaken. With respect to other ‘natural’ hazards, it is widely reported that mitigation can pay. However, the lack of such an evidence base in relation to landslides in developing countries hinders advocacy amongst decision makers for expenditure on ex-ante measures. This research addresses these limitations directly by developing and applying an integrated risk assessment and cost–benefit analysis of physical landslide mitigation measures implemented in an unplanned community in the Eastern Caribbean. In order to quantify the level of landslide risk reduction achieved, landslide hazard and vulnerability were modelled (before and after the intervention), and project costs, direct and indirect benefits were monetised. It is shown that the probability of landslide occurrence has been substantially reduced by implementing surface-water drainage measures and that the benefits of the project outweigh the costs by a ratio of 2.7–1. This paper adds to the evidence base that ‘mitigation pays’ with respect to landslide risk in the most vulnerable communities—thus strengthening the argument for ex-ante measures. This integrated project evaluation methodology should be suitable for adoption as part of the community-based landslide mitigation project cycle, and it is hoped that this resource, and the results of this study, will stimulate further such programmes.     

Structural and stratigraphic problems of the Argylla Formation near Mary Kathleen,Queensland

Rocks formerly mapped as Lower Proterozoic Argylla Formation near Mary Kathleen in northwest Queensland consist of parallel lenses of very deformed schist, quartzite and various types of metaporphyry. Completely intermingled with these are bands of amphibolite and lenses of the adjacent Wonga Granite. Finite ductile strains of 65–80% maximum shortening have been measured; these have produced transposition on both a mesoscopic and macroscopic scale. It is shown that the major stratigraphic boundaries are much shallower than the steeply dipping, constantly oriented unit boundaries. Intrusive relationships and structural criteria indicate that all the lithologies found within the mapped boundaries of the Argylla Formation are chronologically separate. This is confirmed by mapping in the much less deformed area near Winston Churchill Mine to the north. It is concluded that an original sedimentary pile was intruded first by dolerite dyke swarms and then by acid porphyry sills followed by granitic sill‐like instrusions of the Wonga Granite. Subsequent deformation and macroscopic transposition produced the present parallel‐layered structure.

These conclusions differ from currently accepted relationships of the Argylla Formation. Various possibilities are suggested; we favour the view that none of these rock types is equivalent to the defined Argylla Formation, and that the acid porphyries are younger than at Jeast some of the metasediments of the Mary Kathleen Group and may be a precursor of the Wonga Granite intrusion.     

Gravity-flow deposits from the St. Croix Ridge: Depositional history

Gravity-flow sediments from the South Virgin Islands Trough Escarpment (west of the island of St. Croix) contain Late Cretaceous through Late Miocene nannofossils that are well mixed even within individual samples. These sediments, reworked and redeposited in latest Miocene or Early Pliocene, apparently occur within a sequence of Late Miocene-to-recent fan deposits. Marine source beds representing all pre-Pliocene epochs of the Cenozoic and latest Cretaceous must have been exposed along the NW-facing West St. Croix Escarpment. Southward tilting of the St. Croix Ridge has subsequently altered the depositional pattern.