The significance of channel recharge rates for estimating debris‐flow magnitude and frequency     

Matthias Jakob  Michael Bovis  Marian Oden 《地球表面变化过程与地形》2005,30(6):755-766

The quantification of debris‐flow hazard requires estimates of debris‐flow frequency and magnitude. Several methods have been proposed to determine the probable volume of future debris flows from a given basin, but most have neglected to account for debris recharge rates over time, which may lead to underestimation of debris‐flow volumes in basins with rare debris flows. This paper deals with the determination of debris recharge rates in debris‐flow channels based on knowledge of debris storage and the elapsed time since the last debris flow. Data are obtained from coastal British Columbia and a relation is obtained across a sample of basins with similar terrain and climatic conditions. For Rennell Sound on the west coast of the Queen Charlotte Islands, the power‐law relation for area‐normalized recharge rate, R_t, versus elapsed time, t_e was R_t = 0·23t_e^?0·58 with an explained variance of 75 per cent. A difference in recharge rates may exist between creeks in logged and unlogged forested terrain. The power function for undisturbed terrain was R_t = 0·20t_e^?0·49, while the function for logged areas was R_t = 0·30t_e^?0·77. This result suggests that for the same elapsed time since the last debris flow, clearcut gullies tend to recharge at a slower rate than creeks in old growth forest. This finding requires verification, particularly for longer elapsed times since debris flow, but would have important implications for forest resource management in steep coastal terrain. This study demonstrates that commonly used encounter probability equations are inappropriate for recharge‐limited debris flow channels. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Dimensions of the Late Cretaceous-Paleocene Northeast Atlantic rift derived from Cenozoic subsidence     

Jakob Skogseid 《Tectonophysics》1994,240(1-4):225-247

The distribution of Cenozoic subsidence across Northeast Atlantic volcanic margins have been evaluated to define the width of the rift zone and magnitude of extensional deformation. The subsidence profiles are corrected for the effects of lower-crustal magmatic bodies emplaced during continental break-up. The dimensions of the bodies have been derived from the crustal velocity structure. The width of the Late Cretaceous-Paleocene Northeast Atlantic rift zone was more than 300 km, and the lithospheric extension factor increases gradually towards the line of continental separation. A large number of high-quality seismic reflection data tied to scientific and commercial wells reveals that the initiation of extensional deformation preceded continental separation by ˜ 18 m.y. on the Vøring margin, off Norway. These results show that the Northeast Atlantic volcanic margins, commonly considered as typical volcanic margins indeed, have similar dimensions as non-volcanic margins, and as continental rifts. Thus, these margins contrast significantly with previously suggested evolutionary models based on narrow rift zones and formation during rapid lithospheric failure. The wide rift is compatible with volume of igneous rocks observed along these margins, and with a thermal anomaly similar to that associated with production of Northeast Atlantic oceanic lithosphere.  相似文献   

Unmanned aerial vehicle observations of water surface elevation and bathymetry in the cenotes and lagoons of the Yucatan Peninsula,Mexico     

Filippo Bandini  Alejandro Lopez-Tamayo  Gonzalo Merediz-Alonso  Daniel Olesen  Jakob Jakobsen  Sheng Wang  Monica Garcia  Peter Bauer-Gottwein 《Hydrogeology Journal》2018,26(7):2213-2228

Observations of water surface elevation (WSE) and bathymetry of the lagoons and cenotes of the Yucatán Peninsula (YP) in southeast Mexico are of hydrogeological interest. Observations of WSE (orthometric water height above mean sea level, amsl) are required to inform hydrological models, to estimate hydraulic gradients and groundwater flow directions. Measurements of bathymetry and water depth (elevation of the water surface above the bed of the water body) improve current knowledge on how lagoons and cenotes connect through the complicated submerged cave systems and the diffuse flow in the rock matrix. A novel approach is described that uses unmanned aerial vehicles (UAVs) to monitor WSE and bathymetry of the inland water bodies on the YP. UAV-borne WSE observations were retrieved using a radar and a global navigation satellite system on-board a multi-copter platform. Water depth was measured using a tethered floating sonar controlled by the UAV. This sonar provides depth measurements also in deep and turbid water. Bathymetry (wet-bed elevation amsl) can be computed by subtracting water depth from WSE. Accuracy of the WSE measurements is better than 5–7 cm and accuracy of the water depth measurements is estimated to be ~3.8% of the actual water depth. The technology provided accurate measurements of WSE and bathymetry in both wetlands (lagoons) and cenotes. UAV-borne technology is shown to be a more flexible and lower cost alternative to manned aircrafts. UAVs allow monitoring of remote areas located in the jungle of the YP, which are difficult to access by human operators.  相似文献   

Using importers’ windfall savings from oil subsidy reform to enhance international cooperation on climate policies     

Michael Jakob  Jérôme Hilaire 《Climatic change》2015,131(4):465-472

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Achievability of the Paris Agreement targets in the EU: demand-side reduction potentials in a carbon budget perspective     

Vicki Duscha  Alexandra Denishchenkova  Jakob Wachsmuth 《Climate Policy》2019,19(2):161-174

Limiting global warming to ‘well below’ 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase even further to 1.5°C is an integral part of the 2015 Paris Agreement. To achieve these aims, cumulative global carbon emissions after 2016 should not exceed 940 – 390?Gt of CO₂ (for the 2°C target) and 167 – ?48?Gt of CO₂ (for the 1.5°C target) by the end of the century. This paper analyses the EU’s cumulative carbon emissions in different models and scenarios (global models, EU-focused models and national carbon mitigation scenarios). Due to the higher reductions in energy use and carbon intensity of the end-use sectors in the national scenarios, we identify an additional mitigation potential of 26–37 Gt cumulative CO₂ emissions up to 2050 compared to what is currently included in global or EU scenarios. These additional reductions could help to both reduce the need for carbon dioxide removals and bring cumulative emissions in global and EU scenarios in line with a fairness-based domestic EU budget for a 2°C target, while still remaining way above the budget for 1.5°C.

Key policy insights

• Models used for policy advice such as global integrated assessment models or EU models fail to consider certain mitigation potential available at the level of sectors.

• Global and EU models assume significant levels of CO₂ emission reductions from carbon capture and storage to reach the 1.5°C target but also to reach the 2°C target.

• Global and EU model scenarios are not compatible with a fair domestic EU share in the global carbon budget either for 2°C or for 1.5°C.

• Integrating additional sectoral mitigation potential from detailed national models can help bring down cumulative emissions in global and EU models to a level comparable to a fairness-based domestic EU share compatible with the 2°C target, but not the 1.5°C aspiration.

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Routing through open spaces – A performance comparison of algorithms     

Stefan Hahmann  Jakob Miksch  Bernd Resch  Johannes Lauer  Alexander Zipf 《地球空间信息科学学报》2018,21(3):247-256

Abstract

Finding the shortest path through open spaces is a well-known challenge for pedestrian routing engines. A common solution is routing on the open space boundary, which causes in most cases an unnecessarily long route. A possible alternative is to create a subgraph within the open space. This paper assesses this approach and investigates its implications for routing engines. A number of algorithms (Grid, Spider-Grid, Visibility, Delaunay, Voronoi, Skeleton) have been evaluated by four different criteria: (i) Number of additional created graph edges, (ii) additional graph creation time, (iii) route computation time, (iv) routing quality. We show that each algorithm has advantages and disadvantages depending on the use case. We identify the algorithms Visibility with a reduced number of edges in the subgraph and Spider-Grid with a large grid size to be a good compromise in many scenarios.  相似文献   

The role of debris supply conditions in predicting debris flow activity     

Michael J. Bovis  Matthias Jakob 《地球表面变化过程与地形》1999,24(11):1039-1054

Debris flow frequency and magnitude were determined for 33 basins in southwest British Columbia. Basins were first classified as either weathering-limited or transport-limited using a discriminant function based on debris-contributing area, an area-weighted terrain stability number, and drainage density. Multiple regression was used to predict magnitude, peak discharge, frequency and activity (frequency times magnitude) within each group of basins. Model performance was improved by stratifying the total sample of debris flow basins into weathering-and transport-limited groups. Explained variance increased by an average of 15 per cent in the transport-limited sample, indicating that sediment supply conditions in the more active basins are fundamental in predicting debris flow activity. An independent test of the regression models with 11 basins yielded generally good results for debris flow magnitude and peak discharge. Prediction of debris flow frequency proved problematical in weathering-limited basins. The methods developed here provide estimates of debris flow attributes in basins for which few data on past events are available. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Climate change effects on landslides along the southwest coast of British Columbia   总被引：3，自引：0，他引：3  

Matthias Jakob  Steven Lambert   《Geomorphology》2009,107(3-4):275-284

Antecedent rainfall and short-term intense rainfall both contribute to the temporal occurrence of landslides in British Columbia. These two quantities can be extracted from the precipitation regimes simulated by climate models. This makes such models an attractive tool for use in the investigation of the effect of global warming on landslide frequencies.In order to provide some measure of the reliability of models used to address the landslide question, the present-day simulation of the antecedent precipitation and short-term rainfall using the daily data from the Canadian Centre for Climate Modelling and Analysis model (CGCM) is compared to observations along the south coast of British Columbia. This evaluation showed that the model was reasonably successful in simulating statistics of the antecedent rainfall but was less successful in simulating the short-term rainfall.The monthly mean precipitation data from an ensemble of 19 of the world's global climate models were available to study potential changes in landslide frequencies with global warming. Most of the models were used to produce simulations with three scenarios with different levels of prescribed greenhouse gas concentrations during the twenty-first century. The changes in the antecedent precipitation were computed from the resulting monthly and seasonal means. In order to deal with models' suspected difficulties in simulating the short-term precipitation and lack of daily data, a statistical procedure was used to relate the short-term precipitation to the monthly means.The qualitative model results agree reasonably well, and when averaged over all models and the three scenarios, the change in the antecedent precipitation is predicted to be about 10% and the change in the short-term precipitation about 6%. Because the antecedent precipitation and the short-term precipitation contribute to the occurrence of landslides, the results of this study support the prediction of increased landslide frequency along the British Columbia south coast during the twenty-first century.  相似文献   

Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes     

Jakob K. Jakobsen  Christian Tegner  C. Kent Brooks  Adam J. R. Kent  Charles E. Lesher  Troels F. D. Nielsen  Michael Wiedenbeck 《Contributions to Mineralogy and Petrology》2010,159(1):61-79

Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47.4–49.0 wt.% SiO₂, 13.4–14.9 wt.% Al₂O₃ and 10.7–14.1 wt.% FeO^T. These compositions are lower in FeO^T and higher in SiO₂ than previous estimates and have distinct La/Sm_N and Dy/Yb_N ratios that link them to the lowermost volcanic succession (Milne Land Formation) of the regional East Greenland flood basalt province. New major- and trace element compositions for the FG-1 dyke swarm, previously taken to represent Skaergaard magmas, overlap with the entire range of the regional flood basalt succession and do not form a coherent suite of Skaergaard like melts. These dykes are therefore re-interpreted as feeder dykes throughout the main phase of flood basalt volcanism.  相似文献   

Dating a small impact crater: An age of Kaali crater (Estonia) based on charcoal emplaced within proximal ejecta          下载免费PDF全文

A. Losiak  E. M. Wild  W. D. Geppert  M. S. Huber  A. Jõeleht  A. Kriiska  A. Kulkov  K. Paavel  I. Pirkovic  J. Plado  P. Steier  R. Välja  J. Wilk  T. Wisniowski  M. Zanetti 《Meteoritics & planetary science》2016,51(4):681-695

The estimates of the age of the Kaali impact structure (Saaremaa Island, Estonia) provided by different authors vary by as much as 6000 years, ranging from ~6400 to ~400 before current era (BCE). In this study, a new age is obtained based on ¹⁴C dating charred plant material within the proximal ejecta blanket, which makes it directly related to the impact structure, and not susceptible to potential reservoir effects. Our results show that the Kaali crater was most probably formed shortly after 1530–1450 BCE (3237 ± 10 ¹⁴C yr BP). Saaremaa was already inhabited when the bolide hit the Earth, thus, the crater‐forming event was probably witnessed by humans. There is, however, no evidence that this event caused significant change in the material culture (e.g., known archeological artifacts) or patterns of human habitation on Saaremaa.  相似文献