Sea‐cliff retreat and shore platform widening: steady‐state equilibrium?

We challenge the notion of steady‐state equilibrium in the context of progressive cliff retreat on micro‐tidal coasts. Ocean waves break at or close to the abrupt seaward edge of near‐horizontal shore platforms and then rapidly lose height due to turbulence and friction. Conceptual models assume that wave height decays exponentially with distance from the platform edge, and that the platform edge does not erode under stable sea‐level. These assumptions combine to a steady‐state view of Holocene cliff retreat. We argue that this model is not generally applicable. Recent data show that: (1) exponential decay in wave height is not the most appropriate conceptual model of wave decay; (2) by solely considering wave energy at gravity wave frequencies the steady‐state model neglects a possible formative role for infragravity waves. Here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances (and longer timescales) than imaginable under the established conceptual model. Copyright © 2013 John Wiley & Sons, Ltd.     

Trends in the aggregated rate of pre-eruptive volcano-tectonic seismicity at Kilauea volcano, Hawaii

Accelerating rates of volcano-tectonic (VT) earthquakes are commonly observed during volcanic unrest. Understanding the repeatability of their behaviour is essential to evaluating their potential to forecast eruptions. Quantitative eruption forecasts have focused on changes in precursors over intervals of weeks or less. Previous studies at basaltic volcanoes in frequent eruption, such as Kilauea in Hawaii and Piton de La Fournaise on Réunion, suggest that VT earthquake rates tend to follow a power-law acceleration with time about 2 weeks before eruption, but that this trend is often obscured by random fluctuations (or noise) in VT earthquake rate. These previous studies used a stacking procedure, in which precursory sequences for several eruptions are combined to enhance the signal from an underlying acceleration in VT earthquake rate. Such analyses assume a common precursory trend for all eruptions. This assumption is tested here for the 57 eruptions and intrusions recorded at Kilauea between 1959 and 1984. Applying rigorous criteria for selecting data (e.g. maximum depth; restricting magnitudes to be greater than the completeness magnitude, 2.1), we find a much less pronounced increase in the aggregate rate of earthquakes than previously reported. The stacked trend is also strongly controlled by the behaviour of one particular pre-eruptive sequence. In contrast, a robust signal emerges among stacked VT earthquake rates for a subset of the eruptions and intrusions. The results are consistent with two different precursory styles at Kilauea: (1) a small proportion of eruptions and intrusions that are preceded by accelerating rates of VT earthquakes over intervals of weeks to months and (2) a much larger number of eruptions that show no consistent increase until a few hours beforehand. The results also confirm the importance of testing precursory trends against data that have been filtered according to simple constraints on the spatial distribution and completeness magnitude of the VT earthquakes.     

Hydrogeology of northern Sierra de Chiapas,Mexico: a conceptual model based on a geochemical characterization of sulfide-rich karst brackish springs

Conspicuous sulfide-rich karst springs flow from Cretaceous carbonates in northern Sierra de Chiapas, Mexico. This is a geologically complex, tropical karst area. The physical, geologic, hydrologic and chemical attributes of these springs were determined and integrated into a conceptual hydrogeologic model. A meteoric source and a recharge elevation below 1,500 m are estimated from the spring-water isotopic signature regardless of their chemical composition. Brackish spring water flows at a maximum depth of 2,000 m, as inferred from similar chemical attributes to the produced water from a nearby oil well. Oil reservoirs may be found at depths below 2,000 m. Three subsurface environments or aquifers are identified based on the B, Li⁺, K⁺ and SiO₂ concentrations, spring water temperatures, and CO₂ pressures. There is mixing between these aquifers. The aquifer designated Local is shallow and contains potable water vulnerable to pollution. The aquifer named Northern receives some brackish produced water. The composition of the Southern aquifer is influenced by halite dissolution enhanced at fault detachment surfaces. Epigenic speleogenesis is associated with the Local springs. In contrast, hypogenic speleogenesis is associated with the brackish sulfidic springs from the Northern and the Southern environments.     

Three-Dimensional Modeling of Storm Surge and Inundation Including the Effects of Coastal Vegetation

Two-dimensional (2D) and three-dimensional (3D) hydrodynamic models are used to simulate the hurricane-induced storm surge and coastal inundation in regions with vegetation. Typically, 2D storm surge models use an enhanced Manning coefficient while 3D storm surge models use a roughness height to represent the effects of coastal vegetation on flow. This paper presents a 3D storm surge model which accurately resolves the effects of vegetation on the flow and turbulence. First, a vegetation-resolving 1DV Turbulent Kinetic Energy model (TKEM) is introduced and validated with laboratory data. This model is both robust enough to accurately model flows in complex canopies, while compact and efficient enough for incorporation into a 3D storm surge-wave modeling system: Curvilinear Hydrodynamics in 3D-Surface WAves Nearshore (CH3D-SWAN). Using the 3D vegetation-resolving model, three numerical experiments are conducted. In the first experiment, comparisons are made between the 2D Manning coefficient approach and the 3D vegetation-resolving approach for simple wind-driven flow. In a second experiment, 2D and 3D representations of vegetation produce similar inundations from the same hurricane forcing, but differences in momentum are found. In a final experiment, varying inundation between seemingly analogous 2D and 3D representations of vegetation are demonstrated, pointing to a significant scientific need for data within wetlands during storm surge events. This study shows that the complex flow structures within vegetation canopies can be accurately simulated using a vegetation-resolving 3D storm surge model, which can be used to assess the feasibility for future wetland restoration projects.     

Reclamation influence and background geochemistry of neutral saline soils in the Po River Delta Plain (Northern Italy)

Reclaimed neutral saline sulphate soils constitute a large part of the eastern part of Po Plain lowlands, where intensive agricultural activities take place. The knowledge of their geochemical features is essential to develop the best management practices capable to preserve this threatened environment. With this aim, three boreholes were drilled in an agricultural field and a typical reclaimed soil profile has been characterized for major and trace element, pH, electrical conductivity, redox conditions and water-soluble anions and ammonium. Statistical analysis (cluster analysis and principal component analysis) has been used to understand the relationship between elements and grain size. The soil profile is characterized by high salinity and high organic matter contents responsible for high chloride, sulphate, and ammonium concentrations. Heavy metal content is naturally high, since Po Plain sediments are the result of ultramafic rocks erosion; in addition, organic matter tends to concentrate heavy metals by adsorption, mainly in peaty horizons. As a consequence of chemical and zootechnical fertilization, high NO₃ ^? contents have been found in the top soil, thus enhancing the risk of nitrate discharge in the water system, especially in relation to extreme climatic events.     

Discussion of “The Bushveld Complex,South Africa: formation of platinum–palladium,chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large,relatively slowly cooling,subsiding magma chamber” by Maier et al. (2013) Miner Deposita 48:1–56

We believe the hypothesis presented by Maier et al. (Miner Deposita 48:1–56, 2012) for the formation of the various ore bodies in the Bushveld Complex to be overly simplistic, and we raise concerns that some of our work, used in support of this hypothesis, has been misrepresented. The formation of both diverse metalliferous layers (platinum-group element (PGE) reefs and Ti-magnetite layers) and some discordant (pipe) ore deposits has been ascribed by Maier et al. to the single unifying process of hydrodynamic sorting. The problem faced by authors of universal hypotheses for the Bushveld Complex is the sheer size and complexity of the intrusion. We disagree with many aspects of the overall Maier et al. model and have also identified several minor errors on maps and photographs, although some of these do not have a material effect on the model. The nature and origin of the layering is, however, too complex a topic to deal with in the context of this commentary, and we restrict ourselves to noting that our preferred hypothesis, namely the incremental buildup of layering from numerous episodes of replenishment, by different magma lineages, is consistent with field relationships. Our hypothesis for the origin of the ultramafic-hosted PGE-rich reefs, i.e., lateral mixing, is applicable to economically mineralized reefs (Mitchell and Scoon, Econ Geol 102:971–1009, 2007) and poorly mineralized layers such as the Pseudoreef harzburgite (Scoon and De Klerk, Canad Mineral 25:51–77, 1987) and the chromitite layers below the UG2 (Scoon and Teigler, Econ Geol 89:1094–1121, 1994).     

Renewed Geoarchaeological Investigations of Mwanganda's Village (Elephant Butchery Site), Karonga,Malawi

The site of Mwanganda's Village, located along a paleochannel in northern Malawi, is one of only a few sites that have characterized the Middle Stone Age (MSA) of Malawi for decades (Clark & Haynes, 1970 ; Clark et al., 1970 ; Kaufulu, 1990 ). The Malawi Earlier‐Middle Stone Age Project has re‐examined the site using new mapping and chronometric tools in order to reinterpret the site's significance within the context of current debates surrounding human origins and the potential role the environment played in shaping human behavior. The new data do not support the previous hypothesis that the site was an elephant butchery location (contra Clark & Haynes, 1970 ; Clark et al., 1970 ; Kaufulu, 1990 ). Instead, the evidence shows successive colonization of riparian corridors by MSA hunter‐gatherers focused on exploiting localized resources during periods of generally humid climates while other lakes desiccated across Africa. We challenge the hypothesis that stable and intermediately high lake levels within the African Rift Valley System (sensu Trauth et al., 2010 ) catalyzed the evolution of regional interaction networks between 42 and 22 ka. Instead, we interpret the evidence to suggest that regional variants of technology persist into the late MSA as foragers focused on exploiting resources from local catchments.     

Analysis of landslide causes and associated damages in the Kashmir Himalayas of Pakistan

This article deals with the analysis of landslide causes and associated damages in the Kashmir Himalayas of Pakistan. The present study is based on Muzaffarabad, which lies in the lesser Himalayas. Geologically, the Kashmir Himalaya is the young and most dynamic system in the world. In Muzaffarabad, mostly, people live on the fragile mountain slopes, and therefore, they are highly vulnerable to the risk of landslides. To achieve the objectives of the study, data were collected both from primary and secondary sources. Primary data were obtained through intensive field work and human perception survey, while secondary data were obtained from the related line agencies. The analysis reveals that in the study area, immature geology, active seismic zone, wide range of temperature and seasonal rain are the major physical factors, whereas human interventions on the fragile slopes are intensifying factors which in effect contribute to the landslide incidence. As a result, the adverse impacts on housing, sources of livelihood earnings and human casualties are escalating day-by-day. There are several implementing agencies which are responsible for reducing the risk of landsliding. So far, these agencies have not reduced the landslide damages rather their intensity and frequency have been increased especially after 2005 Kashmir earthquake.     

Evidence for temporally coherent increases in the abundance of small Discostella (Bacillariophyceae) species over the past 200 years among boreal lakes from the Experimental Lakes Area (Canada)

Journal of Paleolimnology - Increased relative abundances and accumulation rates of the small, centric diatom Discostella have been recorded in numerous paleolimnological investigations of north...     

Sequestration rental policies and price path of carbon

Abstract

Carbon rental has been suggested as a way of providing incentives to sequester carbon in biomass in the context of emissions trading systems for GHG emissions. A rental system works by issuing a credit for sequestered carbon that must be repaid after some fixed term. Rental systems avoid many of the difficulties of ensuring the permanence of sequestered carbon that exist in other institutional arrangements. This article adapts the results of Herzog et al. (2003) to argue that a rental system requires that carbon prices rise more slowly than the value of alternative investments in order to provide adequate incentives, and that there are good reasons to believe that this may not happen. Proponents need to directly address this potential difficulty in advancing arguments that carbon rental should be adopted as policy.