Landslide-risk mapping in a developing hilly area with limited information on landslide occurrence

Landslide risk was assessed at the basin scale, in terms of specific landslide risk, in a region with limited information on landslide occurrence. Specific landslide risk was mapped by combining the landslide-hazard map and vulnerability of the elements at risk. The assessment of landslide hazard was based both on the spatial-temporal probability of landslide occurrence and on landslide intensity. In this regard, a major problem to resolve was the landslide-occurrence probability. Thus, several procedures were performed, including remote-sensing-based techniques, photointerpretation, dendrochronology, and press news. On the other hand, vulnerability was studied based empirically on the inferred relationship between the hazard class and the likely damage that the landslide would cause. In this way, vulnerability was shown in terms of expected degree of loss by using property-loss criteria. The results reveal that specific landslide risk in the area is mainly low, since just 2.26% of zone showed either a possible or a likely specific landslide risk. Buildings, irrigation structures, and main roads cover 2.6% of the study zone while representing approximately 80% of the specific landslide risk. By contrast, croplands cover almost 50% of the area but represent only 7.1% of specific landslide risk. The results indicate that, although this empirical methodology is subject to some level of uncertainty, it can provide reasonable estimates of specific landslide risk over a large area despite lacking information on landslide occurrence.     

Using legacy data to reconstruct the past? Rescue,rigour and reuse in peatland geochronology

There is a growing interest in the rescue and reuse of data from past studies (so-called legacy data). Data loss is alarming, especially where natural archives are under threat, such as peat deposits. Here we develop a workflow for reuse of legacy radiocarbon dates in peatland studies, including a rigorous quality assessment that can be tailored to specific research questions and study regions. A penalty is assigned to each date based on criteria that consider taphonomic quality (i.e., sample provenance) and dating quality (i.e., sample material and method used). The weights of quality criteria may be adjusted based on the research focus, and resulting confidence levels may be used in further analyses to ensure robustness of conclusions. We apply the proposed approach to a case study of a (former) peat landscape in the Netherlands, aiming to reconstruct the timing of peat initiation spatially. Our search yielded 313 radiocarbon dates from the 1950s to 2019. Based on the quality assessment, the dates—of highly diverse quality—were assigned to four confidence levels. Results indicate that peat initiation for the study area first peaked in the Late Glacial (~14,000 cal years BP), dropped during the Boreal (~9,500 cal years BP) and showed a second peak in the Subboreal (~4,500 cal years BP). We tentatively conclude that the earliest peak was mostly driven by climate (Bølling–Allerød interstadial), whereas the second was probably the result of Holocene sea level rise and related groundwater level rise in combination with climatic conditions (hypsithermal). Our study highlights the potential of legacy data for palaeogeographic reconstructions, as it is cost-efficient and provides access to information no longer available in the field. However, data retrieval may be challenging, and reuse of data requires that basic information on location, elevation, stratigraphy, sample and laboratory analysis are documented irrespective of the original research aims.     

Probing the deep critical zone beneath the Luquillo Experimental Forest,Puerto Rico

Recent work has suggested that weathering processes occurring in the subsurface produce the majority of silicate weathering products discharged to the world's oceans, thereby exerting a primary control on global temperature via the well‐known positive feedback between silicate weathering and CO₂. In addition, chemical and physical weathering processes deep within the critical zone create aquifers and control groundwater chemistry, watershed geometry and regolith formation rates. Despite this, most weathering studies are restricted to the shallow critical zone (e.g. soils, outcrops). Here we investigate the chemical weathering, fracturing and geomorphology of the deep critical zone in the Bisley watershed in the Luquillo Critical Zone Observatory, Puerto Rico, from two boreholes drilled to 37.2 and 27.0 m depth, from which continuous core samples were taken. Corestones exposed aboveground were also sampled. Weathered rinds developed on exposed corestones and along fracture surfaces on subsurface rocks slough off of exposed corestones once rinds attain a thickness up to ~1 cm, preventing the corestones from rounding due to diffusion limitation. Such corestones at the land surface are assumed to be what remains after exhumation of similar, fractured bedrock pieces that were observed in the drilled cores between thick layers of regolith. Some of these subsurface corestones are massive and others are highly fractured, whereas aboveground corestones are generally massive with little to no apparent fracturing. Subsurface corestones are larger and less fractured in the borehole drilled on a road where it crosses a ridge compared with the borehole drilled where the road crosses the stream channel. Both borehole profiles indicate that the weathering zone extends to well below the stream channel in this upland catchment; hence weathering depth is not controlled by the stream level within the catchment and not all of the water in the watershed is discharged to the stream. Copyright © 2013 John Wiley & Sons, Ltd.     

Bedforms: views and new perspectives from the third international workshop on Marine and River Dune Dynamics (MARID3)

This Commentary introduces a Special Issue of Earth Surface Processes and Landforms dedicated to the memory of Stephen Coleman (1966–2012) who sadly passed away on July 23, 2012. Stephen was an incredible enthusiast for the study of bedforms and made seminal contributions to our knowledge and understanding of flow, sediment transport and bedform dynamics. Stephen presented a keynote address at MARID 3, which has led to this Special Issue (see Coleman SE, Nikora VI. 2011. Fluvial dunes: initiation, characterization, flow structure. Earth Surface Processes and Landforms 36 : 39–57. DOI. 10.1002/esp.2096) and was always keen to discuss research, from theory to techniques to experiments. He was always generous with his time and touched many with the influence of his thoughts and intellect. Our community has lost an outstanding scientist and Stephen will be greatly missed by us all. Copyright © 2012 John Wiley & Sons, Ltd.     

The Imaging Magnetograph eXperiment (IMaX) for?the?Sunrise Balloon-Borne Solar Observatory

The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter built by four institutions in Spain that flew on board the Sunrise balloon-borne solar observatory in June 2009 for almost six days over the Arctic Circle. As a polarimeter, IMaX uses fast polarization modulation (based on the use of two liquid crystal retarders), real-time image accumulation, and dual-beam polarimetry to reach polarization sensitivities of 0.1%. As a spectrograph, the instrument uses a LiNbO₃ etalon in double pass and a narrow band pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the high-Zeeman-sensitive line of Fe i at 5250.2 Å and observes all four Stokes parameters at various points inside the spectral line. This allows vector magnetograms, Dopplergrams, and intensity frames to be produced that, after reconstruction, reach spatial resolutions in the 0.15??C?0.18 arcsec range over a 50×50 arcsec field of view. Time cadences vary between 10 and 33 s, although the shortest one only includes longitudinal polarimetry. The spectral line is sampled in various ways depending on the applied observing mode, from just two points inside the line to 11 of them. All observing modes include one extra wavelength point in the nearby continuum. Gauss equivalent sensitivities are 4 G for longitudinal fields and 80 G for transverse fields per wavelength sample. The line-of-sight velocities are estimated with statistical errors of the order of 5??C?40 m?s^?1. The design, calibration, and integration phases of the instrument, together with the implemented data reduction scheme, are described in some detail.     

Cellular automata to describe seismicity: A review

Cellular Automata have been used in the literature to describe seismicity. We first historically introduce Cellular Automata and provide some important definitions. Then we proceed to review the most important models, most of them being variations of the spring-block model proposed by Burridge and Knopoff, and describe the most important results obtained from them. We discuss the relation with criticality and also describe some models that try to reproduce real data.     

Protection of groundwater intended for human consumption: a proposed methodology for defining safeguard zones

Carbonate aquifers constitute a water reserve of essential importance for human supply. For this, it is necessary to establish suitable protection measures in order to achieve the good status of groundwater bodies intended for human supply according to the requirements of the Water Framework Directive. The objective of this paper is to present a methodology to define safeguard zones for the protection of carbonate groundwater bodies intended for human consumption. To do this, firstly the risk of groundwater contamination is evaluated through a combination of characterising pressures and the evaluation of the intrinsic vulnerability to contamination. Secondly, the existing water abstraction points are identified and their zones of contribution are delineated in order to establish priorities when defining protective measures in the region. Finally, the existing wellhead protection areas and those defined according to the proposed methodology must be integrated into the delineated safeguard zones. The results obtained in a carbonate groundwater body in southern Spain are consistent with the existing quality data and they show the percentage of land that must be protected to preserve the quality of water intended for human consumption, thus facilitating their future integration into adequate land use planning tools.     

Avoiding the Ghetto through hope and fear: an analysis of immanent technology using ideal types

With over one hundred million smart-phone users in the world, mobile, spatially-aware devices are radically altering how individuals move through and experience both physical and social environments. This article presents a theoretical and methodological framework for engaging the emerging geoweb as part of a longer tradition of research into society and technology. A close reading of Microsoft’s Pedestrian Route Production patent, dubbed the “avoid ghetto GPS”, is used to construct two ideal type futures—one hopeful and one frightening. One where spatial technology ensures efficiency, safety, and new forms of coordination, while the other algorithmically sorts society by race and class. Despite not yet and potentially never existing, the patent offers a viable means through which potential futures are made real in the present. Through comparative analysis of these futures, their underlying commonalities are drawn out, revealing the relationship between technology and the delimitation of human experience. This analysis avoids grand narratives and teleological arguments, while making it possible to draw forth the unthought acceptance within each ideal type for the future: the continuing shift of human life itself towards a teleological, always already-calculated standing-reserve. The work on technology of Martin Heidegger and Herbert Marcuse (re)situate the geoweb within long-standing theoretical work on technology and its role in society, modernity, and capitalism.     

Carbonate concretions—explained

Carbonate concretions are common features of sedimentary rocks of all geological ages. They are most obvious in sandstones and mudstones as ovoid bodies of rock that protrude from natural outcrops: clearly harder or better cemented than their host rocks. Many people are excited by finding fossils in the centre of mudstone‐hosted concretions ( Fig. 1 ) but spend little time wondering why the fossils are so well preserved. While the study of concretions has benefitted from the use of advanced analytical equipment, simple observations in the field can also help to answer many questions. For example, in cliff sections, original sedimentary beds and sedimentary structures can be traced right through concretions ( Fig. 2 ): so it can be deduced that the concretion clearly formed after these depositional structures were laid down. In this article we explain how and where concretions form and discuss the evidence, ranging from outcrop data to sophisticated laboratory analyses, which can be used to determine their origins. The roles of microbes, decaying carcasses, compaction and groundwaters are highlighted. Concretions not only preserve fossils but can also subdivide oil, gas and water reservoirs into separate compartments.

Figure 1 Open in figure viewer PowerPoint An early diagenetic carbonate concretion split in half to reveal an ammonite retaining its original aragonite shell, from the Maastrichtian of Antarctica. Image courtesy of Alistair Crame (British Antarctic Survey, NERC). Lens cap is 6 cm.     

A method of accelerating transport simulation when groundwater pumping is simulated

In solving groundwater transport problems with numerical models, the computation time (CPU processing time) of transport simulation is approximately inversely proportional to the transport time-step size. Therefore, large time-step sizes are favorable for achieving short computation time. However, transport time-step size must be sufficiently small to avoid numerical instability if an explicit scheme is used (and to guarantee enough model accuracy if an implicit scheme is used). For a transport model involving groundwater pumping, a small transport time-step size is often required due to the high groundwater velocities near the pumping well. Small grid spacing often specified near the pumping well also limits the time-step size. This paper presents a method to increase transport time-step size in a transport model when groundwater pumping is simulated. The key to this approach is to numerically decrease the groundwater seepage velocities in grid cells near the pumping well by increasing the effective porosity so that the transport time-step size can be increased without violating stability constraints. Numerical tests reveal that by using the proposed method, the computation time of transport simulation can be reduced significantly, while the transport simulation results change very little.