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1.
Features of Sand-dust Deposits in Harbin City, China 总被引：1，自引：0，他引：1
XIE Yuanyun ZHANG yan HE Kui ZHOU Jia KANG Chunguo 《中国地理科学(英文版)》2006,16(4):327-333
1 Introduction The sand-dust storm weather, induced by special at- mospheric circulation in specifically geologic and geo- graphic environment, is disastrous one with little prob- ability and excessive harm. In China, the sand-dust storm frequency of every 10 years had increased from 4 times in the 1950s to 23 times in the 1990s (Zhuang et al., 2001). The sand-dust weather occurring in a large area of the northern China in the spring of 2002 had attracted much attention. People are gradually… 相似文献
2.
LI Yong LIU Jingling CHEN Xiaoqing WEI Fangqiang 《山地科学学报》2007,4(1):071-076
Debris flows consist of grains of various sizes ranging from 10~(-6) m ～1 m. Field observations in the Jiangjia Gully (JJG) and other sites throughout China indicate that the grain size distribution of sediment in debris flows can be characterized by an exponential function fit to the cumulative distribution. The exponent value for the function varies by location and may be useful in distinguishing between debris flows from different valleys. For example, minimum values and ranges of the exponent are associated with the high frequency of debris flows in the JJG. Furthermore, the distribution presents piecewise fractality (i.e. scaling laws hold in various ranges of the grain size) and we propose that the fractal structure determines the matrix and that the fractal dimension plays a crucial role in material exchange between a debris flow and the substrate it flows over. Finally, the empirical data support an exponential relation between grain composition and non-dimensional shear stress for the critical state of the channel. Overall we propose a material-determinism approach to studying debris flows which contrasts with the enviro-determinism that has dominated much recent work in this field. 相似文献
3.
Introduction Agriculture, which is the dominant sector in the mountains, is generally stagnant. Degradation of the natural resource base has contributed to an increase in frequency and intensity of landslides, gully formation, soil erosion, declining soil fertility, reduced per capita availability and fragmentation of land, and reduced flow of water for irrigation. This has led to steady decline in crop yields (5~30 %) or stagnation that caused food shortages at varying degrees among mountain … 相似文献
4.
Submarine landslides occur frequently on most continental margins. They are effective mechanisms of sediment transfer but also a geological hazard to seafloor installations. In this paper, submarine slope stability is evaluated using a 2D limit equilibrium method. Considerations of slope, sediment, and triggering force on the factor of safety (FOS) were calculated in drained and undrained (Φ=0) cases. Results show that submarine slopes are stable when the slope is <16° under static conditions and without a weak interlayer. With a weak interlayer, slopes are stable at <18° in the drained case and at <9° in the undrained case. Earthquake loading can drastically reduce the shear strength of sediment with increased pore water pressure. The slope became unstable at >13° with earthquake peak ground acceleration (PGA) of 0.5 g; whereas with a weak layer, a PGA of 0.2 g could trigger instability at slopes >10°, and >3° for PGA of 0.5 g. The northern slope of the South China Sea is geomorphologically stable under static conditions. However, because of the possibility of high PGA at the eastern margin of the South China Sea, submarine slides are likely on the Taiwan Bank slope and eastern part of the Dongsha slope. Therefore, submarine slides recognized in seismic profiles on the Taiwan Bank slope would be triggered by an earthquake, the most important factor for triggering submarine slides on the northern slope of the South China Sea. Considering the distribution of PGA, we consider the northern slope of the South China Sea to be stable, excluding the Taiwan Bank slope, which is tectonically active. 相似文献
5.
Gently dipping fractures subjected to river incision are widely distributed on rock slopes. In this paper, a rock slope on the Nujiang River (China) is investigated to study the role of gently dipping fractures in the rock slopes evolution. Detailed field surveys indicate that gentle fractures are concentrated in four main zones. Moreover, the kinematics of the fracture system suggest that the genesis of these fractures can be synthesized into a progressive evolution model. This model indicates that the joints begin with the formation of an array of en echelon cracks that are subjected to continued crack elongation and shearing before ultimately approaching one another and interacting to form a complex joint system. Geomechanical analysis is performed to reveal the mechanisms of this genesis, and three main fracture patterns are identified based on the slope stress and are classified with respect to the slope evolution. Based on the detail field investigations and the evolutionary history of the river valley, we propose that intermittent incision by the river was the main factor contributing to the concentrated distribution of gently dipping joints. 相似文献
6.
Landslides & debris flows formation from gravelly soil surface erosion and particle losses in Jiangjia Ravine 总被引：1，自引：1，他引：0
Gravelly soils are made up of gravel, sand, silt and clay. They are widely used in engineering applications such as rock-fill dams with clay cores, which are the main researches at present. The strength and mechanical properties of the gravelly soils are affected by the content of coarse grain, fine particles, and their adhesive states. These Properties can be verified by laboratory unconsolidated undrained triaxial tests with grain size less than 5 mm and by large scale direct-shear tests with original grain content. Fine particles of the loose gravelly slopes are released under rainfalls, alternated the structures and mechanical properties, even affected the slope stability. There are a series of large scale direct-shear tests with different coarse grain contents to study the influence of fine particles releasing and migration, results showed the strength behavior of the gravelly soils were affected by the coarse grain content （5） and the inflection coarse grain contents. In order to study the erosion features of the gravelly soil slopes on rainfall conditions and the slopes stability alteration, we had carried out one sort of artificial rainfall local and model experiments, the runoff sediment contents were monitored during the experiments. Result showed that the shapes of the slopes surface transformed periodically, runoff sediment contents were divided into five phases according to the experiment phenomena, runoff sediment contents maintained downtrend during the rain time and the downtrend was obviouslyinterpreted by one descend belt no matter the rainfall intensity and the slope angels. Particle size analysis released the deposit on the slope surface lost almost all of the clay, most of the silt and sand after the experiments, this meant the fine particles releasing, migration and accumulation process on condition of rainfall resulted in the instability factor of the slopes even induced landslide or debris flow. 相似文献
7.
Soil organic carbon pools in particle-size fractions as affected by slope gradient and land use change in hilly regions, western Iran 总被引：3，自引：3，他引：0
Parisa Mokhtari KARCHEGANI Shamsollah AYOUBI Mohammad Reza MOSADDEGHI Naser HONARJOO 《山地科学学报》2012,9(1):87-95
This study was conducted to explore the effects of topography and land use changes on particulate organic carbon(POC),particulate total nitrogen(PTN),organic carbon(OC) and total nitrogen(TN) associated with different size primary particle fractions in hilly regions of western Iran.Three popular land uses in the selected site including natural forest(NF),disturbed forest(DF) and cultivated land(CL) and three slope gradients(0-10 %,S1,10-30 %,S2,and 30-50%,S3) were employed as the basis of soil sampling.A total of 99 soil samples were taken from the 0-10 cm surface layer in the whole studied hilly region studied.The results showed that the POC in the forest land use in all slope gradients was considerably more than the deforested and cultivated lands and the highest value was observed at NF-S1 treatment with 9.13%.The values of PTN were significantly higher in the forest land use and in the down slopes(0.5%) than in the deforested and cultivated counterparts and steep slopes(0.09%) except for the CL land use.The C:N ratios in POC fraction were around 17-18 in the forest land and around 23 in the cultivated land.In forest land,the silt-associated OC was highest among the primary particles.The enrichment factor of SOC,EC,was the highest for POC.For the primary particles,EC of both primary fractions of silt and clay showed following trend for selected land uses and slope gradients:CL> DF> NF and S3 > S2> S1.Slope gradient of landscape significantly affected the OC and TN contents associated with the silt and clay particles,whereas higher OC and TN contents were observed in lower positions and the lowest value was measured in the steep slopes.Overall,the results showed that native forest land improves soil organic carbon storage and can reduce the carbon emission and soil erosion especially in the mountainous regions with high rainfall in west of Iran. 相似文献
8.
Deformation and failure of high slope impact the construction and operation safety of highway in the mountainous areas. The
deformation and failure are mainly caused by poor design which normally has not well combined with the geological conditions
and unplanned construction. Therefore, effective design and construction management should be conducted for ensuring a successful
construction without damage and risk. In light of the reality of high slope construction along highway in the Huangshan area,
this paper proposes a technical procedure for dynamic design and construction management of high slopes along highway in the
mountainous area. The proposed construction management scheme is divided into three phases, i.e., 1) design phase, 2) preparation
phase of excavation, and 3) construction phase. During the design phase, experiences and lessons learnt from the design and
construction of other high slopes along highway in the same region are summarized. The number of slopes and slope height should
be optimized from the aspects of route selection and route form. During the preparation phase of excavation, “Excavation Permit
Management System” should be adopted, and construction scheme should be made by the construction unit, then the scientific
research and design unit determine whether it guarantees slope stability and makes optimization measures. During the construction
phase, the scientific research unit would make proposal of optimization design, and apply the achievements of scientific research
into practice through common efforts of various units based on the understanding of excavation and investigation. The management
system mentioned above is adopted to conduct dynamic design and construction management for more than 90 slopes along the
Huangshan — Taling — Taolin Expressway, and successful results of application have been achieved. 相似文献
9.
Slope failure in loess terrains of Northern China during spring thawing period is closely related to the freeze-thaw cycling that surface soils inevitably experienced. Field surveys were carried out on natural and artificial slopes in thirteen surveying sites located in the Northern Shaanxi, the center of Loess Plateau, covering five characteristic topographic features including tablelands, ridges, hills, gullies and valleys. Based on the scale that is involved in freeze-thaw cycling, the induced failures can be classified into three main modes, i.e., erosion, peeling and thaw collapse, depending on both high porosity and loose cementation of loess that is easily affected. Model tests on loess slopes with gradients of 53.1°, 45.0° and 33.7° were carried out to reveal the heat transfer, water migration and deformation during slope failure. The surface morphology of slopes was photographed, with flake shaped erosion and cracks noted. For three slope models, time histories for the thermal regime exhibit three obvious cycles of freeze and thaw andthe maximum frost depth develops downwards as freeze-thaw cycling proceeds. Soil water in the unfrozen domain beneath was migrated towards the slope surface, as can be noticed from the considerable change in the unfrozen water content, almost synchronous with the variation of temperature. The displacement in both vertical and horizontal directions varies over time and three obvious cycles can be traced. The residual displacement for each cycle tends to grow and the slopes with higher gradients are more sensitive to potentially sliding during freeze-thaw cycling. 相似文献
10.
A quantitative analysis of the spatial pattern of rural settlements in the upper reaches of the Minjiang River was made with
the major data sources being the relevant ETM image and the national geographical database of China (including contour line,
river and road) at the scale of 1:250 000, and using image interpretation and field investigation to obtain spatial information
on rural settlements. The results of the spatial analysis technique of GIS and correlation analysis showed that most settlements
(78.2 %) were located in the mountain area at 1500 ∼ 2700 m altitude, and almost half in the arid valley area. More than 80.0
% of settlements had their slopes above 15°. Most settlements had good access to water resources, roads and communications,
and tended to cluster close to the road network rather than the river. About half of the rural settlements in the study area
were relatively concentrated, while the others were decentralized. Those with higher altitude usually had land with steep
slope, inconvenient water and road accesses, and were located far apart from each other. In view of such a situation, further
research should be done to make reasonable countermeasures on these settlements for better living conditions and ecosystem
stability. 相似文献
11.
Introduction A set of reddish clay-silt-sized sediments named red clay underlying the Quaternary loess-paleosol sequence widely distribute in the Chinese Loess Plateau. The thickness of the red clay sediments ranges from decades of meters to over 100 m (Evan et al.1991,Mo and Derbyshire 1991, SUN et al. 1997&1998, DING et al. 1999, GUO et al. 2001, QIANG et al. 2001). Previous studies show that not only loess-paleosol (e.g.LIU et al.1985,AN et al.1990,DING et al.1992),but also red … 相似文献
12.
YU Fei WANG De-xiang SHI Xiao-xiao YI Xian-feng HUANG Qing-ping HU You-ning 《山地科学学报》2013,10(5):845-853
Natural seedling regeneration and tree establishment are affected by various environmental factors.In this study,we established eight,eight,six,and four independent forest stands(each stand was further divided into five subplots) respectively based on the altitudinal gradient,stand density,slope location,and slope aspect to investigate the effects of environmental factors on tree seedling regeneration in a pine-oak mixed forest.The results indicated that the seedling density was significantly higher at altitudes of 1,283 m to 1,665 m,whereas the sapling density did not differ with altitudes.The seedling and sapling density decreased significantly at 1,835 m.The seedling densities on the upper slopes were much higher than those on the middle and lower slopes,whereas the sapling density had no difference.The sapling density decreased gradually from the southwest(20°-75°) whereas it increased on the shady slopes to the northeast(40°).The seedling density increased from southwest(20°) to northeast(40°).The seedling and sapling densities increased with the stand density(850 trees ha-1to 1,525 trees ha-1) whereas the sapling density was significantly lower in stands(1,900 trees ha-1).Principal components analysis showed that the slope aspect and stand density had more important roles in tree regeneration in this study region compared with the other two factors.Therefore,our findings suggest that it will be beneficial to keep stands at a moderate density on shady slopes.Appropriate thinning of higher density stands is also expected to promote the natural regeneration of pine-oak mixed forest. 相似文献
13.
Sub-tidal (1.04–25 day) current fluctuations during winter/spring on the continental shelf off Savannah, Georgia (32°N) and
off St. Augustine, Florida (30°N) were compared with records of local wind stress components and GulfStream position. (Acoustic
travel time and bottom pressure measurements at stations on the continental slope were combined to determine main, thermocline
depth, as an indicator of Gulf Stream displacement). Relative wind influences increased towards the coast. GulfStream influence
increased towards the shelf-break and towards the surface. Off Savannah, the Gulf Stream influence was predominately at 12
day period and was negligible at the 45 m isobath. Off St. Augustine, its influence was predominately at 4 day period and
was appreciable at the 40 m isobath (but negligeable at the 28 m isobath). Linear predictions of currents from wind and Gulf
Stream account for ∼80% of the observed variance. Similar methods of studying and predicting the wind—and Kuroshio-influenced
currents on the East China Shelf are proposed. 相似文献
14.
Diagenetic control of magnetic susceptibility variation in Core MD98-2172 from the Eastern Timor Sea
Detailed mineral magnetic measurements, integrated with grain-size distribution and X-ray diffraction (XRD) analyses, were
made on the marine sediments of Core MD98-2172, retrieved from the Eastern Timor Sea. Values of magnetic susceptibility in
this core drop sharply down-core from ∼3.85 m deep below sediment/water interface and are very low at ∼5.35 m. However, both
XRD and grain-size distribution results show no sudden change in terrigenous input during sedimentation. Mineral magnetic
results indicate that the depth of ∼3.85 m may be an oxic/anoxic boundary. Therefore, the sediments below ∼3.85 m have been
subjected to intense reductive diagenesis, whereas the sediments above ∼3.85 m are seldom affected. The magnetic properties
of the sediments shallower than 3.85 m are dominated by pseudo-single domain (PSD) magnetite, with little down-core variation
in its content and grain size. Below ∼3.85 m, the magnetic mineral assemblages that have survived in the sediments may record
different stages of the reductive diagenesis: (1) the sediments from the 3.85–5.35 m interval are at the stage of iron oxide
reduction; PSD magnetite is the major magnetic contributor, but it becomes less abundant and coarser down-core; (2) the sediments
below ∼5.35 m are at the stage of sulphate reduction; ferrimagnetic minerals almost vanish and paramagnetic minerals contribute
to down-core susceptibility variations, including pyrite as evidenced by high-temperature magnetic susceptibility measurements.
However, the susceptibility variations below ∼5.35 m of Core MD98-2172 show obvious periodicity, despite the intense effect
of reductive diagenesis. Furthermore, the down-core susceptibility variations are coincident with fluctuations in the quantity
of fine detrital particles (<8 μm), which may come mainly from the advection of the Indonesia Throughflow (ITF) and/or river
input from Timor. Therefore, for Core MD98-2172, susceptibility variation below ∼5.35 m, which potentially correspond to fluctuations
in the quantity of fine particles, may record the histories of the development of the ITF and precipitation on Timor. 相似文献
15.
On the basis of scaling analysis,this paper presents a frontal geostrophic dynamic system which canbe used to describe the dynamics of an isolated bottom eddy and shows that five possible dynamicsubregimes are included in the system.A particle-in-cell method is used to investigate the behavior of the eddy in the two dynamic subregimes,with 1)nonlinear effect(ε)relevant to the sloping bottom-inducedbeta effect(β_1)and 2)seamount-induced beta effect(β_2)dominant.In the dynamic subregime of β_1～ ε～10~(-2)and β_2=0,the eddy can keep as a whole for a long time and migrates for a long distance.Inthe dynamic subregime where the seamount-induced beta effect (β_2～10~(-1))is dominant,the seamounttraps the water particles,causing the eddy to break up into a discrete set of eddies moving around the seamount. 相似文献
16.
TheQuaternalypaleo--environmentoftheLushan,HuangshanandTianmumountainsisasignificantacademicproblemtowhichmuchattentionhasbeenpaidbymanyresearchersingeosciencecircle.Manyscholarshavestudiedtheproblemandgotalotofachivementsoverthepastyears(Lee,1933;Lee,1936;Lee,1947;Ren,1953;Huang,1963;Li,1974;Shi,1989).HOWever,identicalviewsandconclusionshavenotbeenreachedyetuptillnow,especiallylackingofcomprehensivestudyforsedimentsintheseregions.Inrecentyears,applyingsedimentalcomprehensiveindexgotfromv… 相似文献
17.
In laboratory conditions, effects of rearing temperature and stocking density were examined on hatching of fertilized egg
and growth of auricularia larvae of Apostichopus japonicus respectively. Data series like larval length and density, metamorphic time, and survival rate of the larvae were recorded.
Statistics showed that for A. japonicus, survival rate (from fertilized egg to late auricularia) decreased significantly with the increasing rearing temperature
(P<0.05). At different temperatures SGR was statistically significant as well (P<0.05) from day 1, and maximal SGR was found on day 9 at 24°C (159.26±3.28). This study clearly indicated that at low temperature
(<24°C), metamorphic rate was remarkably higher than at higher temperature (>26°C). Hatching rate was significantly different
between 0.2–5 ind./ml groups and 20–50 ind./ml groups. Rearing larvae at the higher density had the smaller maximal-length,
whereas needed longer time to complete metamorphosis. This study suggested that 21°C and 0.4 ind./ml can be used as the most
suitable rearing temperature and stocking density for large -scale artificial breeding of A. japonicus’s larvae. 相似文献
18.
《山地科学学报》2020,17(1):156-172
Loose deposits, rainfall and topography are three key factors that triggering debris flows.However, few studies have investigated the effects of loose deposits on the whole debris flow process.On June 28, 2012, a catastrophic debris flow occurred in the Aizi Valley, resulting in 40 deaths.The Aizi Valley is located in the Lower Jinsha River,southwestern Sichuan Province, China. The Aizi Valley debris flow has been selected as a case for addressing loose deposits effects on the whole debris flow process through remote sensing, field investigation and field experiments. Remote sensing interpretation and laboratory experiments were used to obtain the distribution and characteristics of the loose deposits, respectively. A field experiment was conducted to explore the mechanics of slope debris flows, and another field investigation was conducted to obtain the processes of debris flow formation, movement and amplification. The results showed that loose deposits preparation, slope debris flow initiation,gully debris flow confluence and valley debris flow amplification were dominated by the loose deposits.Antecedent droughts and earthquake activities may have increased the potential for loose soil sources in the Aizi Valley, which laid the foundation for debris flow formation. Slope debris flow initiated under rainfall, and the increase in the water content as well as the pore water pressure of the loose deposits were the key factors affecting slope failure. The nine gully debris flows converged in the valley, and the peak discharge was amplified 3.3 times due to a blockage and outburst caused by a large boulder. The results may help in predicting and assessing regional debris flows in dry-hot and seismic-prone areas based on loose deposits, especially considering large boulders. 相似文献
19.
Topographic influence on wetland distribution and change in Maduo County, Qinghai-Tibet Plateau, China 总被引：1，自引：0，他引：1
Accurate information on the spatial distribution and temporal change of wetlands is vital to devise effective measures for their protection. This study uses satellite images in 1994 and 2001 to assess the effects of topography and proximity to channels on wetland change in Maduo County on the Qinghai-Tibet Plateau, western China. In 1994 wetlands in the study area extended over 6,780.0 km2. They were distributed widely throughout the county, with a higher concentration in the south, and were especially prominent close to streams. The pattern of wetlands demonstrated a bell-shaped distribution curve with elevation, ranging over hill slopes with gradients from 0-19°, the commonest gradient being around 3°. Although the aspects of these hill slopes range over all directions, there is a lower concentration of wetlands facing east and southeast. The extent of wetlands in 2001 decreased to 6,181.1 km2. Marked spatial differentiation in the pattern of wetlands is evident, as their area increased by 1,193.3 km2 at lower elevations but decreased by 1,792.2 km2 at higher ground, resulting in a net decrease of 598.8 km2. In areas with a gradient <2° or >9° the area of wetlands remained approximately consistent from 1994-2001. Newly retained wetlands are situated in relatively flat lowland areas, with no evident preference in terms of aspect. Wetlands on north-, east- and northeast-facing hillslopes with a bearing of 1-86° were more prone to loss of area than other orientations. The altered pattern of wetland distribution from higher to lower elevation on north-facing slopes coincided with the doubling of annual temperature during the same period, suggesting that climate warming could be an important cause. 相似文献
20.
The fatty acid compositions of seston and Calanus sinicus were investigated to study trophic relationships in Jiaozhou Bay. Principal component analysis was carried out to ordinate the fatty acid patterns of seston in stations and months. The results showed that diatoms were most abundant in the phytoplankton at station A5 (located in the northwest of the bay:36°9′N, 120°20′E) and least abundant at station D7 (located outside of the bay: 35°59′N, 120°26′E). By contrast, dinoflagellates were most abundant at station D7 and least abundant at station A5. According to the annual variations of 16:1ω7 and 18:4ω3/ 16:1ω7, diatoms flourished mainly in spring and summer, while dinoflagellates bloomed exclusively in summer. A distinctive feature of the fatty acid composition of C. sinicus was the prevalence of 20:5ω3 and 22:6ω3. The higher content of 16:1ω7 over 18:4ω3 in females indicated that diatoms contributed more than dinoflagellates to the diet of C. sinicus. The feeding intensity of C. sinicus on diatoms was higher in spring and autumn than in other seasons. The herbivorous indicators 20:1 and 22:1 were comparatively low, suggesting that besides phytoplankton, C. sinicus might feed on a wider range of particles including organic detritus, bacteria and small copepods. 相似文献