East Asian monsoon variation and climate changes in Jeju Island, Korea, during the latest Pleistocene to early Holocene     

Seung Hyoun Lee  Yong Il Lee  Ho Il Yoon 《Quaternary Research》2008,70(2):265-274

A 4.96-m-long sediment core from the Hanon paleo-maar in Jeju Island, Korea was studied to investigate the paleoclimatic change and East Asian monsoon variations during the latest Pleistocene to early Holocene (23,000-9000 cal yr BP). High-resolution TOC content, magnetic susceptibility, and major element composition data indicate that Jeju Island experienced the coldest climate around 18,000 cal yr BP, which corresponds to the last glacial maximum (LGM). Further, these multi-proxy data show an abrupt shift in climatic regime from cold and arid to warm and humid conditions at around 14,000 cal yr BP, which represents the commencement of the last major deglaciation. After the last major deglaciation, the TOC content decreased from 13,300 to 12,000 cal yr BP and from 11,500 to 9800 cal yr BP, thereby reflecting the weakening of the summer monsoon. The LGM in Jeju Island occurred later in comparison with the Chinese Loess Plateau. Such a disparity in climatic change events between central China and Jeju Island appears to be caused by the asynchrony between the coldest temperature event and the minimum precipitation event in central China and by the buffering effect of the Pacific Ocean.  相似文献   

U–Pb SHRIMP zircon geochronology and T–t–d history of the Kampa Dome, southern Tibet     

M.C. Quigley  Y. Liangjun  C. Gregory  A. Corvino  M. Sandiford  C.J.L. Wilson  L. Xiaohan 《Tectonophysics》2008,446(1-4):97-113

Structural, petrographic and geochronologic studies of the Kampa Dome provide insights into the tectonothermal evolution of orogenic crust exposed in the North Himalayan gneiss domes of southern Tibet. U–Pb ion microprobe dating of zircons from granite gneiss exposed at the deepest levels within the dome yields concordia ²⁰⁶Pb/²³⁸U age populations of 506 ± 3 Ma and 527 ± 6 Ma, with no evidence of new zircon growth during Himalayan orogenesis. However, the granite contains penetrative deformation fabrics that are also preserved in the overlying Paleozoic strata, implying that the Kampa granite is a Cambrian pluton that was strongly deformed and metamorphosed during Himalayan orogenesis. Zircons from deformed leucogranite sills that cross-cut Paleozoic metasedimentary rocks yield concordant Cambrian ages from oscillatory zoned cores and discordant ages ranging from ca. 491–32 Ma in metamict grains. Since these leucogranites clearly post-date the metasedimentary rocks they intrude, the zircons are interpreted as xenocrysts that are probably derived from the Kampa granite. The Kampa Dome formed via a series of progressive orogenic events including regional ~ N–S contraction and related crustal thickening (D₁), predominately top-to-N ductile shearing and crustal extension (D₂), top-to-N brittle–ductile faulting and related folding on the north limb of the dome, localized top-to-S faulting on the southern limb of the dome, and crustal doming (D₃), and continued N–S contraction, E–W extension and doming (D₄). Structural and geochronologic variability amongst adjacent North Himalayan gneiss domes may reflect changes in the magnitude of crustal exhumation along the North Himalayan antiform, possibly relating to differences in the mid-crustal geometry of the exhuming fault systems.  相似文献   

Morphological analysis of the drainage system in the Eastern Alps   总被引：2，自引：1，他引：1  

Jrg Robl  Stefan Hergarten  Kurt Stüwe 《Tectonophysics》2008,460(1-4):263-277

We study the morphology of the major rivers draining the Eastern Alps to test whether the active tectonics of this part of the orogen is reflected in the shape of channel profiles of the river network. In our approach we compare channel profiles measured from digital elevation models with numerically modelled channel profiles using a stream power approach. It is shown that regions of high stream power coincide largely with regions of highest topography and largest uplift rates, while the forelands and the Pannonian Basin are characterised by a significantly lower stream power. From stream power modelling we conclude that there is young uplift at the very east of the Eastern Alps, in the Bohemian Massif and in the Pohorje Range. The impact of the Pleistocene glaciations is explored by comparing properties of rivers that drain in proximal and distal positions relative to the ice sheet during the last glacial maximum. Our analysis shows that most knick points, wind gaps and other non-equilibrium features of catchments covered by ice during the last glaciations (Salzach, Enns) can be correlated with glacial processes. In contrast the ice free catchments of the Mur and Drava are characterized by channels in morphological equilibrium at the first approximation and are showing only weak evidence of the strong tectonic activity within these catchments. Finally, the channel profiles of the Adige and the divide between the upper Rhine and Danube catchments differ significantly from the other catchments. We relate this to the fact that the Adige and the Rhine respond to different base levels from the remainder of the Eastern Alps: The Adige may preserve a record from the Messininan base level change and the Rhine is subject to the base level lowering in the Rhine Graben.  相似文献   

Simultaneous transport of water and solutes under transient unsaturated flow conditions — A case study     

B. K. Purandara  N. Varadarajan  B. Venkatesh 《Journal of Earth System Science》2008,117(4):477-487

The imbalance between incoming and outgoing salt causes salinization of soils and sub-soils that result in increasing the salinity of stream-flows and agriculture land. This salinization is a serious environmental hazard particularly in semi-arid and arid lands. In order to estimate the magnitude of the hazard posed by salinity, it is important to understand and identify the processes that control salt movement from the soil surface through the root zone to the ground water and stream flows. In the present study, Malaprabha sub-basin (up to dam site) has been selected which has two distinct climatic zones, sub-humid (upstream of Khanapur) and semi-arid region (downstream of Khanapur). In the upstream, both surface and ground waters are used for irrigation, whereas in the downstream mostly groundwater is used. Both soils and ground waters are more saline in downstream parts of the study area. In this study we characterized the soil salinity and groundwater quality in both areas. An attempt is also made to model the distribution of potassium concentration in the soil profile in response to varying irrigation conditions using the SWIM (Soil-Water Infiltration and Movement) model. Fair agreement was obtained between predicted and measured results indicating the applicability of the model.  相似文献   

Implications of Kali-Hindon inter-stream aquifer water balance for groundwater management in western Uttar Pradesh     

Rashid Umar  M. Muqtada A. Khan  Izrar Ahmed  Shakeel Ahmed 《Journal of Earth System Science》2008,117(1):69-78

The Kali-Hindon inter-stream region extends over an area of 395 km² within the Ganga-Yamuna interfluve. It is a fertile tract for sugarcane cultivation. Groundwater is a primary resource for irrigation and industrial purposes. In recent years, over-exploitation has resulted in an adverse impact on the groundwater regime. In this study, an attempt has been made to calculate a water balance for the Kali-Hindon inter-stream region. Various inflows and outflows to and from the aquifer have been calculated. The recharge due to rainfall and other recharge parameters such as horizontal inflow, irrigation return flow and canal seepage were also evaluated. Groundwater withdrawals, evaporation from the water table, discharge from the aquifer to rivers and horizontal subsurface outflows were also estimated. The results show that total recharge into the system is 148.72 million cubic metres (Mcum), whereas the total discharge is 161.06 Mcum, leaving a deficit balance of −12.34 Mcum. Similarly, the groundwater balance was evaluated for the successive four years. The result shows that the groundwater balance is highly sensitive to variation in rainfall followed by draft through pumpage. The depths to water level are shallow in the canal-irrigated northern part of the basin and deeper in the southern part. The pre-monsoon and post-monsoon water levels range from 4.6 to 17.7 m below ground level (bgl) and from 3.5 to 16.5 m bgl respectively. It is concluded that the groundwater may be pumped in the canal-irrigated northern part, while withdrawals may be restricted to the southern portion of the basin, where intense abstraction has led to rapidly falling water table levels.  相似文献   

华北克拉通破坏与岩石圈减薄   总被引：20，自引：2，他引：18  

嵇少丞  王茜  许志琴 《地质学报》2008,82(2):174-193

古太古代（约4.0 Ga）时地球上可能只有一个超级大陆, 它的岩石圈厚度高达400 km。在早元古代,这个超级大陆减薄、裂解成十几块,每块中心是太古宙岩石,边缘是元古宙岩石,且各块厚度不等（150~350km）。从元古宙之后这些被称之为稳定克拉通的大陆岩石圈就一直漂游在地幔软流圈之上。中国华北地块就是这些克拉通之一,与众不同的是它在中生代时遭受了第二次破坏,岩石圈厚度从古生代时的180~200 km 减少到现今的80~100 km。本文作者从流变学的视角出发,围绕华北克拉通破坏和岩石圈减薄这一核心问题,从  相似文献   

Use of sinkhole and specific capacity distributions to assess vertical gradients in a karst aquifer     

Kurt J. McCoy  Mark D. Kozar 《Environmental Geology》2008,54(5):921-935

The carbonate-rock aquifer in the Great Valley, West Virginia, USA, was evaluated using a database of 687 sinkholes and 350 specific capacity tests to assess structural, lithologic, and topographic influences on the groundwater flow system. The enhanced permeability of the aquifer is characterized in part by the many sinkholes, springs, and solutionally enlarged fractures throughout the valley. Yet, vertical components of subsurface flow in this highly heterogeneous aquifer are currently not well understood. To address this problem, this study examines the apparent relation between geologic features of the aquifer and two spatial indices of enhanced permeability attributed to aquifer karstification: (1) the distribution of sinkholes and (2) the occurrence of wells with relatively high specific capacity. Statistical results indicate that sinkholes (funnel and collapse) occur primarily along cleavage and bedding planes parallel to subparallel to strike where lateral or downward vertical gradients are highest. Conversely, high specific capacity values are common along prominent joints perpendicular or oblique to strike. The similarity of the latter distribution to that of springs suggests these fractures are areas of upward-convergent flow. These differences between sinkhole and high specific capacity distributions suggest vertical flow components are primarily controlled by the orientation of geologic structure and associated subsurface fracturing.  相似文献   

Evaluation of approaches to calculate debris-flow parameters for hazard assessment   总被引：2，自引：0，他引：2  

Marcel Hürlimann  Dieter Rickenmann  Vicente Medina  Allen Bateman 《Engineering Geology》2008,102(3-4):152

Many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment. The present article reviews the empirical, analytical, simple flow routing and numerical techniques. All these techniques were applied to back-calculate a debris flow, which occurred in 1982 at La Guingueta catchment, in the Eastern Pyrenees. A sensitivity analysis of input parameters was carried out, while special attention was paid to the influence of rheological parameters. We used the Voellmy fluid rheology for our analytical and numerical modelling, since this flow resistance law coincided best with field observations. The simulation results indicated that the “basal” friction coefficients rather affect the runout distance, while the “turbulence” terms mainly influence flow velocity. A comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones. The values of our rheological parameters calibrated at La Guingueta agree with data back-calculated for other debris flows. Empirical relationships represent another method to estimate total runout distance. The results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions, which were the basis for their development. With regards to the simple flow routing algorithm, this methods could satisfactorily simulate the total area affected by the 1982 debris flow, but it was not able to directly calculate total runout distance and velocity. Finally, a suggestion on how different runout prediction methods can be applied to generate debris-flow hazard maps is presented. Taking into account the definition of hazard and intensity, the best choice would be to divide the resulting hazard maps into two types: “final hazard maps” and “preliminary hazard maps”. Only the use of numerical models provided final hazard maps, because they could incorporate different event magnitudes and they supplied output-values for intensity calculation. In contrast, empirical relationships and flow routing algorithms, or a combination of both, could be applied to create preliminary hazard maps. The present study only focussed on runout prediction methods. Other necessary tasks to complete the hazard assessment can be looked up in the “Guidelines for landslide susceptibility, hazard and risk zoning” included in this Special Issue.  相似文献   

What controls dead-ice melting under different climate conditions? A discussion     

Anders Schomacker   《Earth》2008,90(3-4):103-113

In the geological record, hummocky dead-ice moraines represent the final product of the melt-out of dead-ice. Processes and rates of dead-ice melting in ice-cored moraines and at debris-covered glaciers are commonly believed to be governed by climate and debris-cover properties. Here, backwasting rates from 14 dead-ice areas are assessed in relation to mean annual air temperature, mean summer air temperature, mean annual precipitation, mean summer precipitation, and annual sum of positive degree days. The highest correlation was found between backwasting rate and mean annual air temperature. However, the correlation between melt rates and climate parameters is low, stressing that processes and topography play a major role in governing the rates of backwasting. The rates of backwasting from modern glacial environments should serve as input to de-icing models for ancient dead-ice areas in order to assess the mode and duration of deposition.A challenge for future explorations of dead-ice environments is to obtain long-term records of field-based monitoring of melt progression. Furthermore, many modern satellite-borne sensors have high potentials for recordings of multi-temporal Digital Elevation Models (DEMs) for detection and quantification of changes in dead-ice environments. In recent years, high-accuracy DEMs from airborne laser scanning altimetry (LiDAR) are emerging as an additional data source. However, time series of high-resolution aerial photographs remain essential for both visual inspection and high-resolution stereographic DEM production.  相似文献   

Assessment of disaster resilience capacity of hillslope communities with high risk for geological hazards   总被引：2，自引：0，他引：2  

Su-Chin Chen  Jhy-Wei Ferng  Yu-Ting Wang  Ting-Yeh Wu  Jieh-Jiuh Wang   《Engineering Geology》2008,98(3-4):86-101

This study presents a novel preparedness assessment method for assessing hazard mitigation and environmental planning of hillslope communities. A professional questionnaire was utilized to weight each indicator. Communities in Hsinchu, Taichung and Nantou counties with debris flow hazards were taken as study samples. Debris flow risk and landslide susceptibility for each community were determined using Geographic Information System (GIS) technology and logistic regression analysis. Thus, a novel risk assessment method for evaluating disaster resilience capacity of hillslope communities was established. This method was then applied to assess casualties caused by Typhoon Herb in 1996 and Typhoon Mindulle in 2004. Additionally, the analytical results generated by this assessment method were discussed with the aim of developing references for implementation of risk analysis, increasing the effectiveness of disaster mitigation, and reducing future loss of life and property.  相似文献