The impact of storm-triggered landslides on sediment dynamics and catchment-wide denudation rates in the southern Central Range of Taiwan following the extreme rainfall event of Typhoon Morakot     

Chia-Yu Chen  Sean D. Willett  A. Joshua West  Simon Dadson  Niels Hovius  Marcus Christl  J. Bruce H. Shyu 《地球表面变化过程与地形》2020,45(3):548-564

Extreme erosion events can produce large short-term sediment fluxes. Such events complicate erosion rates estimated from cosmogenic nuclide concentrations in river sediment by providing sediment with a concentration different from the long-term basin average. We present a detrital ¹⁰Be study in southern Taiwan, with multiple samples obtained in a time sequence bracketing the 2009 Typhoon Morakot, to assess the impact of landslide sediment on ¹⁰Be concentrations (N¹⁰Be) in river sediment. Sediment samples were collected from 13 major basins, two or three times over the last decade, to observe the temporal variation of N¹⁰Be. Landslide inventories with time intervals of 5–6 years were used to quantify sediment flux changes. A negative correlation between N¹⁰Be and landslide areal density indicates dilution of N¹⁰Be by landslide sediment. Denudation rates estimated from the diluted N¹⁰Be can be up to three times higher than the lowest rate derived from the same basins. Observed increases imply that, 3 years after the passage of Typhoon Morakot, fluvial channels still contain a considerable amount of sediment provided by hillslope landslides during the event. However, higher N¹⁰Be in 2016 samples indicate that the contribution from landslide sediment at the sampled grain size has decreased with time. The correlation between changes in N¹⁰Be and landslide area and volume is not strong, likely resulting from the stochastic and complex nature of sediment transport. To simultaneously evaluate the volume of landslide-derived sediment and estimate the background denudation rate, associated with less impulsive sediment supply, we constructed a sediment-mixing model with the time series of N¹⁰Be and landslide inventories. The spatial pattern of background erosion rate in southern Taiwan is consistent with the regional tectonic framework, indicating that the landscape is evolving mainly in response to the tectonic forcing, and this signal is modified, but not obscured by impulsive sediment supply. © 2019 John Wiley & Sons, Ltd.  相似文献   

Bound and mobile soil water isotope ratios are affected by soil texture and mineralogy,whereas extraction method influences their measurement     

Rachel E. Adams  Ayumi Hyodo  Toby SantaMaria  Cynthia L. Wright  Thomas W. Boutton  Jason B. West 《水文研究》2020,34(4):991-1003

Questions persist about interpreting isotope ratios of bound and mobile soil water pools, particularly relative to clay content and extraction conditions. Interactions between pools and resulting extracted water isotope composition are presumably related to soil texture, yet few studies have manipulated the bound pool to understand its influence on soil water processes. Using a series of drying and spiking experiments, we effectively labelled bound and mobile water pools in soils with varying clay content. Soils were first vacuum dried to remove residual water, which was then replaced with heavy isotope-enriched water prior to oven drying and spiking with heavy isotope-depleted water. Water was extracted via centrifugation or cryogenic vacuum distillation (at four temperatures) and analysed for oxygen and hydrogen isotope ratios via isotope ratio mass spectrometry. Water from centrifuged samples fell along a mixing line between the two added waters but was more enriched in heavy isotopes than the depleted label, demonstrating that despite oven drying, a residual pool remains and mixes with the mobile water. Soils with higher clay + silt content appeared to have a larger bound pool. Water from vacuum distillation samples have a significant temperature effect, with high temperature extractions yielding progressively more heavy isotope-enriched values, suggesting that Rayleigh fractionation occurred at low temperatures in the vacuum line. By distinctly labelling bound and mobile soil water pools, we detected interactions between the two that were dependent on soil texture. Although neither extraction method appeared to completely extract the combined bound and mobile (total water) pool, centrifugation and high temperature cryogenic vacuum distillations were comparable for both δ²H and δ¹⁸O of soil water isotope ratios.  相似文献   

Sedimentology of the continental end‐Permian extinction event in the Sydney Basin,eastern Australia     

Christopher R. Fielding  Tracy D. Frank  Allen P. Tevyaw  Katarina Savatic  Vivi Vajda  Stephen McLoughlin  Chris Mays  Robert S. Nicoll  Malcolm Bocking  James L. Crowley 《Sedimentology》2021,68(1):30-62

Upper Permian to Lower Triassic coastal plain successions of the Sydney Basin in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of palaeoenvironmental change at high southern palaeolatitudes in a continental margin context for the late Permian (Lopingian), across the end‐Permian Extinction interval, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the late Permian and, to a much lesser extent, during the Early Triassic, allowing high‐resolution age determination on the numerous tuff horizons. Palaeobotanical and radiogenic isotope data indicate that the end‐Permian Extinction occurs at the top of the uppermost coal bed, and the Permo‐Triassic boundary either within an immediately overlying mudrock succession or within a succeeding channel sandstone body, depending on locality due to lateral variation. Late Permian depositional environments were initially (during the Wuchiapingian) shallow marine and deltaic, but coastal plain fluvial environments with extensive coal‐forming mires became progressively established during the early late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. However, apart from the loss of peat‐forming mires, no significant long‐term change in depositional style (grain size, sediment‐body architecture, or sediment dispersal direction) was noted across the end‐Permian Extinction (pinpointed by turnover of the palaeoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from these successions. Rather, the end‐Permian Extinction marks the base of a long‐term, progressive trend towards better‐drained alluvial conditions into the Early Triassic. Indeed, the floral turnover was immediately followed by a flooding event in basinal depocentres, following which fluvial systems similar to those active prior to the end‐Permian Extinction were re‐established. The age of the floral extinction is constrained to 252.54 ± 0.08 to 252.10 ± 0.06 Ma by a suite of new Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry U‐Pb ages on zircon grains. Another new age indicates that the return to fluvial sedimentation similar to that before the end‐Permian Extinction occurred in the basal Triassic (prior to 251.51 ± 0.14 Ma). The character of the surface separating coal‐bearing pre‐end‐Permian Extinction from coal‐barren post‐end‐Permian Extinction strata varies across the basins. In basin‐central locations, the contact varies from disconformable, where a fluvial channel body has cut down to the level of the top coal, to conformable where the top coal is overlain by mudrocks and interbedded sandstone–siltstone facies. In basin‐marginal locations, however, the contact is a pronounced erosional disconformity with coarse‐grained alluvial facies overlying older Permian rocks. There is no evidence that the contact is everywhere a disconformity or unconformity.  相似文献   

Unveiling buried aeolian landscapes: reconstructing a late Holocene dune environment using 3D ground-penetrating radar     

Luis Rees-Hughes  Natasha L. M. Barlow  Adam D. Booth  Landis J. West  George Tuckwell  Tim Grossey 《第四纪科学杂志》2021,36(3):377-390

Across the UK, sandy beaches and dunes protect coastal infrastructure from waves and extreme water levels during large-scale storms, while providing important habitats and recreational opportunities. Understanding their long-term evolution is vital in managing their condition in a changing climate. Recently, ground-penetrating radar (GPR) methods have grown in popularity in geomorphological applications, yielding centimetre-scale resolution images of near-surface stratigraphy and structure, thus allowing landscape evolution to be reconstructed. Additionally, abrupt changes in palaeo-environments can be visualized in three dimensions. Although often complemented by core data, GPR allows interpretations to be extended into areas with minimal ground-truth control. Nonetheless, GPR data interpretation can be non-intuitive and ambiguous, and radargrams may not initially resemble the expected subsurface geometry. Interpretation can be made yet more onerous when handling the large 3D data volumes that are facilitated with modern GPR technology. Here we describe the development of novel semi-automated GPR feature-extraction tools, based on ‘edge detection’ and ‘thresholding’ methods, which detect regions of increased GPR reflectivity which can be applied to aid in the reconstruction of a range Quaternary landscapes. Since reflectivity can be related to lithological and/or pore fluid changes, the 3D architecture of the palaeo-landscape can be reconstructed from the features extracted from a geophysical dataset. We present 500 MHz GPR data collected over a buried Holocene coastal dune system in North Wales, UK, now reclaimed for use as an airfield. Core data from the site, reaching a maximum depth 2 m, suggest rapid vertical changes from sand to silty-organic units, and GPR profiles suggest similar lateral complexity. By applying thresholding methods to GPR depth slices, these lateral complexities are effectively and automatically mapped. Furthermore, automatic extraction of the local reflection power yields a strong correlation with the depth variation of organic content, suggesting it is a cause of reflectivity contrast. GPR-interpolated analyses away from core control thus offer a powerful proxy for parameters derived from invasive core logging. The GPR data collected at Llanbedr airfield highlight a complex dune system to a depth of 2.8 m, probably deposited in several phases over ~700 years, similar to elsewhere in North Wales.  相似文献   

Three decades of landslide activity in western Nepal: new insights into trends and climate drivers     

Muñoz-Torrero Manchado  A.  Allen  S.  Ballesteros-Cánovas  J. A.  Dhakal  A.  Dhital  M. R.  Stoffel  M. 《Landslides》2021,18(6):2001-2015

In recent decades, landslide disasters in the Himalayas, as in other mountain regions, are widely reported to have increased. While some studies have suggested a link to increasing heavy rainfall under a warmer climate, others pointed to anthropogenic influences on slope stability, and increasing exposure of people and assets located in harm’s way. A lack of sufficiently high-resolution regional landslide inventories, both spatially and temporally, has prevented any robust consensus so far. Focusing on Far-Western Nepal, we draw on remote sensing techniques to create a regional inventory of 26,350 single landslide events, of which 8778 date to the period 1992–2018. These events serve as a basis for the analyses of landslide frequency relationships and trends in relation to precipitation and temperature datasets. Results show a strong correlation between the annual number of shallow landslides and the accumulated monsoon precipitation (r = 0.74). Furthermore, warm and dry monsoons followed by especially rainy monsoons produce the highest incidence of shallow landslides (r = 0.77). However, we find strong spatial variability in the strength of these relationships, which is linked to recent demographic development in the region. This highlights the role of anthropogenic drivers, and in particular road cutting and land-use change, in amplifying the seasonal monsoon influence on slope stability. In parallel, the absence of any long-term trends in landslide activity, despite widely reported increase in landslide disasters, points strongly to increasing exposure of people and infrastructure as the main driver of landslide disasters in this region of Nepal. By contrast, no climate change signal is evident from the data.

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Climate change,climate justice and the application of probabilistic event attribution to summer heat extremes in the California Central Valley     

Roberto Mera  Neil Massey  David E. Rupp  Philip Mote  Myles Allen  Peter C. Frumhoff 《Climatic change》2015,133(3):427-438

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Ethical and normative implications of weather event attribution for policy discussions concerning loss and damage     

Allen Thompson  Friederike E. L. Otto 《Climatic change》2015,130(3):439-452

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Rock avalanches and other landslides in the central Southern Alps of New Zealand: a regional study considering possible climate change impacts   总被引：3，自引：2，他引：1  

Simon K. Allen  Simon C. Cox  Ian F. Owens 《Landslides》2011,8(1):33-48

Slope instabilities in the central Southern Alps, New Zealand, are assessed in relation to their geological and topographic distribution, with emphasis given to the spatial distribution of the most recent failures relative to zones of possible permafrost degradation and glacial recession. Five hundred nine mostly late-Pleistocene- to Holocene-aged landslides have been identified, affecting 2% of the study area. Rock avalanches were distinguished in the dataset, being the dominant failure type from Alpine slopes about and east of the Main Divide of the Alps, while other landslide types occur more frequently at lower elevations and from schist slopes closer to the Alpine Fault. The pre-1950 landslide record is incomplete, but mapped failures have prevailed from slopes facing west–northwest, suggesting a structural control on slope failure distribution. Twenty rock avalanches and large rockfalls are known to have fallen since 1950, predominating from extremely steep east–southeast facing slopes, mostly from the hanging wall of the Main Divide Fault Zone. Nineteen occurred within 300 vertical metres above or below glacial ice; 13 have source areas within 300 vertical metres of the estimated lower permafrost boundary, where degrading permafrost is expected. The prevalence of recent failures occurring from glacier-proximal slopes and from slopes near the lower permafrost limit is demonstrably higher than from other slopes about the Main Divide. Many recent failures have been smaller than those recorded pre-1950, and the influence of warming may be ephemeral and difficult to demonstrate relative to simultaneous effects of weather, erosion, seismicity, and uplift along an active plate margin.  相似文献   

Structure and evolution of mass transport deposits in the South Caspian Basin,Azerbaijan     

Steve E. J. Richardson  Richard J. Davies  Mark B. Allen  Simon F. Grant 《Basin Research》2011,23(6):702-719

The Quaternary to late Pliocene sedimentary succession along the margin of the South Caspian Basin contains numerous kilometre‐scale submarine slope failures, which were sourced along the basin slope and from the inclined flanks of contemporaneous anticlines. This study uses three‐dimensional (3D) seismic reflection data to visualise the internal structure of 27 mass transport deposits and catalogues the syndepositional structures contained within them. These are used to interpret emplacement processes occurring during submarine slope failure. The deposits consist of three linked structural domains: extensional, translational and compressive, each containing characteristic structures. Novel features are present within the mass transport deposits: (1) a diverging retrogression of the headwall scarp; (2) the absence of a conventional headwall scarp around growth stratal pinch outs; (3) restraining bends in the lateral margin; (4) a downslope increase in the throw of thrust faults. The results of this study shed light on the deformation that occurred during submarine slope failure, and highlight an important geological process in the evolution of the South Caspian Basin margin.  相似文献   

A thematic issue on the geological setting and genesis of volcanogenic massive sulfide (VMS) deposits     

Rodney L. Allen  Fernando Tornos  Jan M. Peter 《Mineralium Deposita》2011,46(5-6):429-430

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