Measurement of debris mass changes and assessment of the dam-break flood potential of earthquake-triggered Hattian landslide dam   总被引：1，自引：1，他引：0  

Ahsan Sattar  Kazuo Konagai  Takashi Kiyota  Takaaki Ikeda  Jorgen Johansson 《Landslides》2011,8(2):171-182

The Hattian landslide, which was triggered by the 2005 Kashmir earthquake, formed one of largest landslide dams in the world and it has posed a serious threat of flooding to people living in the lower reach of the Jhelum River. In order to understand deformation occurring in the body of the dam, physical measurements using a Differential Global Positioning System (DGPS) were conducted. Gradual deformation and slowly developing backward erosion initially were observed, leading eventually to a sudden creation of a deep hollow on the downstream slope of the landslide dam. The dimensions of this eroded gully were determined by laser scanning, and the results showed a significant loss of soil volume and a large change in the body of the dam. A breach formation model was used to predict the outflow hydrograph generated by constant downcutting of dam during a breaching event. A run-off analysis of the outflow hydrograph was conducted to evaluate inundation levels of flood waves in case the dam is breached. Hazardous downstream locations were identified near the junction of the Karli and Jhelum Rivers, suggesting a need for early warning system in order to avoid loss of lives.  相似文献   

Differences in physiological response to increased seawater temperature in nearshore and offshore corals in northern Vietnam   总被引：1，自引：0，他引：1  

Faxneld S  Jörgensen TL  Nguyen ND  Nyström M  Tedengren M 《Marine environmental research》2011,71(3):225-233

Effects of elevated seawater temperature show high spatial heterogeneity and variation within and among coral species. The objective of this study was to investigate how two coral species, Porites lutea and Galaxea fascicularis, from two high latitude reefs differently exposed to chronic disturbance, respond to elevated seawater temperatures. Corals were collected from reefs nearshore (i.e. subjected to high sediment load, higher chlorophyll α concentrations, turbidity etc.) and offshore (i.e. less exposed). The corals were exposed in the lab to gradually increasing temperatures (25.5-33.5?°C) for 72?h after which they were allowed to recover to ambient temperature (25.5?°C) for 24?h. Production and respiration were measured after 24, 48, 72 and 96?h. The results show that P. lutea from nearshore reefs suffered an initial decrease in gross primary production/respiration (GP/R) ratio after 24?h, after only a moderate temperature increase (+2?°C, from 25.5 to 27.5?°C), while there was no difference in GP/R ratio between heat-exposed and controls the other days, indicating that the chronic disturbance in the nearshore reef had no effect on their thermotolerance. Furthermore, P. lutea from the offshore reef showed a decrease in GP/R ratio both after 24?h and 72?h (33.5?°C) of exposure. In comparison, G. fascicularis showed a decrease in GP/R ratio after 48?h, 72?h and 96?h of exposure for the nearshore corals. Also, after 72?h these corals had withdrawn their polyps. There were no differences between heat-treated and controls for the offshore G. fascicularis. This implies that the chronically disturbed G. fascicularis had lower thermotolerance when exposed to a temperature increase. This study, hence, shows that the response of corals to elevated seawater temperature varies with species and environmental background history.  相似文献   

Analysis of spatial temperature variations in regions of massive star formation     

S. Yu. Malafeev  I. I. Zinchenko  L. E. Pirogov  L. E. B. Johansson 《Astronomy Letters》2005,31(4):239-244

Using the 20-m Onsala Observatory telescope (Sweden), we performed observations of the CH₃C₂H(6-5) line toward several regions of massive star formation to estimate the kinetic temperature of the gas and study its variations over the sources. Intense lines were detected in five objects. For these, we estimated the kinetic temperature of the gas near the CS and N₂H⁺ molecular emission peaks by the method of population diagrams. A significant temperature difference between these peaks is noticeable only in W3 and, to a lesser degree, in DR 21. In the remaining cases, it is insignificant. This indicates that the chemical differentiation of the molecules in these regions cannot be associated with temperature variations. The kinetic temperature determined from methyl acetylene observations is usually slightly higher than the temperature estimated from ammonia observations. This is probably because the methyl acetylene emission originates in denser, i.e., deeper and hotter layers of the cloud.  相似文献   

The grazing encounter between IC 2163 and NGC 2207: pushing the limits of observational modelling     

Curtis Struck  Michele Kaufman  Elias Brinks †  Magnus Thomasson  Bruce G. Elmegreen  Debra Meloy Elmegreen 《Monthly notices of the Royal Astronomical Society》2005,364(1):69-90

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Grenvillian and Caledonian evolution of eastern Svalbard – a tale of two orogenies     

Åke Johansson  David G. Gee  Alexander N. Larionov  Yoshihide Ohta  Alexander M. Tebenkov 《地学学报》2005,17(4):317-325

Svalbard is located in the north-west corner of the Barents Sea shelf and the Eurasian Plate, in a key area for interpreting Caledonian and older orogens in the Arctic region. Recent U–Pb dating in the Nordaustlandet Terrane of eastern Svalbard shows this terrane to consist of a Grenville-age basement, overlain by Neoproterozoic to early Palaeozoic platformal sediments, and intruded by Caledonian anatectic granites. Deformation, metamorphism and crustal anatectic magmatism occurred both during the Grenvillian (960–940 Ma) and Caledonian (450–410 Ma) orogenies. This evolution shows great similarities with that of eastern Greenland. In the classical model, eastern Svalbard is placed outboard of central east Greenland in pre-Caledonian time. Alternatively, it may have been located north-east of Greenland and transferred west and rotated anticlockwise during Caledonian continent–continent collision. In the Neoproterozoic, easternmost Svalbard may have been part of a wider area of Grenville-age crust, now fragmented and dispersed around the Arctic.  相似文献   

The galaxy population of intermediate-redshift clusters     

Tomas Dahlén †  Claes Fransson  Göran Östlin  Magnus Näslund 《Monthly notices of the Royal Astronomical Society》2004,350(1):253-266

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A finite element formulation in Lagrangian co-ordinates for heat and fluid flow in compacting sedimentary basins     

Magnus Wangen 《国际地质力学数值与分析法杂志》1993,17(6):401-432

This article presents a numerical model of heat and fluid flow in compacting sedimentary basins formulated in Lagrangian co-ordinates. The Lagrangian co-ordinates are the sediment particle positions of the completely compacted basin. A finite element formulation of excess water pressure and temperature in these Lagrangian co-ordinates is presented, in addition to an equivalent formulation in the real co-ordinates. The later formulation is also Lagrangian of nature, since the elements of the grid in the real co-ordinates always frame the same sediment particles. In other words, it is the Lagrangian grid mapped to the real space. This is done in an iterative loop which solves for excess water pressure, and then updates the real co-ordinates of the sediment particles. By comparing the two finite element formulations it is concluded that the one in real space is the simplest, most efficient and most precise. The model is validated by comparison with two dimensionless one-dimensional solutions, one analytical for the linear case, and one numerical for the non-linear case. Both these one-dimensional solutions are obtained on the unit interval, where the moving top boundary caused by continuous sedimentation is incorporated.  相似文献   

Observations of martian gullies and constraints on potential formation mechanisms: II. The northern hemisphere     

Jennifer L. Heldmann  Ella Carlsson  Henrik Johansson  Owen B. Toon 《Icarus》2007,188(2):324-344

The formation process(es) responsible for creating the observed geologically recent gully features on Mars has remained the subject of intense debate since their discovery. We present new data and analysis of northern hemisphere gullies from Mars Global Surveyor data which is used to test the various proposed mechanisms of gully formation. We located 137 Mars Orbiter Camera (MOC) images in the northern hemisphere that contain clear evidence of gully landforms and analyzed these images in combination with Mars Orbiter Laser Altimeter (MOLA) and Thermal Emission Spectrometer (TES) data to provide quantitative measurements of numerous gully characteristics. Parameters we measured include apparent source depth and distribution, vertical and horizontal dimensions, slopes, orientations, and present-day characteristics that affect local ground temperatures. Northern hemisphere gullies are clustered in Arcadia Planitia, Tempe Terra, Acidalia Planitia, and Utopia Planitia. These gullies form in craters (84%), knobby terrain (4%), valleys (3%), other/unknown terrains (9%) and are found on all slope orientations although the majority of gullies are equator-facing. Most gullies (63%) are associated with competent rock strata, 26% are not associated with strata, and 11% are ambiguous. Assuming thermal conductivities derived from TES measurements as well as modeled surface temperatures, we find that 95% of the gully alcove bases with adequate data coverage lie at depths where subsurface temperatures are greater than 273 K and 5% of the alcove bases lie within the solid water regime. The average alcove length is 470 m and the average channel length is 690 m. Based on a comparison of measured gully features with predictions from the various models of gully formation, we find that models involving carbon dioxide, melting ground ice in the upper few meters of the soil, dry landslide, and surface snowmelt are the least likely to describe the formation of the martian gullies. Although some discrepancies still exist between prediction and observation, the shallow and deep aquifer models remain as the most plausible theories. Interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies. These findings gleaned from the northern hemisphere data are in general agreement with analyses of gullies in the southern hemisphere [Heldmann, J.L., Mellon, M.T., 2004. Icarus 168, 285-304].  相似文献   

    

S. Johansson  V. S. Letokhov 《Astronomy Letters》2004,30(6):433

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Mesoproterozoic to Palaeozoic Evolution of Eastern Svalbard and Barentsia     

ke Johansson  Alexander Larionov  Yoshihide Ohta  Alexander Tebenkov 《Gondwana Research》2001,4(4):645-646

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