Three-dimensional crustal structure of Ascension Island from active source seismic tomography     

C. P. Evangelidis  T. A. Minshull  T. J. Henstock 《Geophysical Journal International》2004,159(1):311-325

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Recharge and aquifer response: Northern Guam Lens Aquifer, Guam, Mariana Islands   总被引：1，自引：0，他引：1  

J. M. U. Jocson  J. W. Jenson  D. N. Contractor   《Journal of Hydrology》2002,260(1-4):231-254

The Northern Guam Lens Aquifer is an island karst aquifer in uplifted young, highly conductive limestone. Calculations of recharge based on differences between daily rainfall and daily pan evaporation suggest that the maximum annual mass of water delivered to the freshwater lens is about 67% of mean annual rainfall. Hydrographs of daily well-level responses plotted against daily rainfall indicate that the rate at which water is delivered to the lens is a function of rainfall intensity and the relative saturation of the vadose zone. Together, these variables determine the degree to which stormwater is shunted into fast flow through preferred pathways that bypass the bedrock matrix, rather than percolating slowly through the bedrock matrix.

Data from the 40-year interval from 1956 to 1995 show that some 17% of rainfall on northern Guam arrives in small amounts (<0.6 cm/day). Most of this light rainfall is probably lost to evapotranspiration. At least another 20% of total rainfall on Guam arrives at very high intensities (>5.0 cm/day), which tend to promote fast flow at the expense of percolation. Rapid recovery of the water table from rapid recharge suggests that the lens either takes such recharge into storage very rapidly, discharges it rapidly without taking it into storage, or some combination of both. Significant vadose buffering of recharge to the lens is indicated by the fact that simulations assuming that the recharge from precipitation received in any given month is transmitted to the lens during the same month consistently over-predict observed peak mean monthly water levels and under-predict the minima.  相似文献   

Tourism and sustainable water supply in Mallorca: a geographical analysis   总被引：3，自引：0，他引：3  

M. Kent  R. Newnham  S. Essex 《Applied geography (Sevenoaks, England)》2002,22(4):717

Problems of sustainability of water supply in tourist resorts are becoming an increasingly common and important issue in applied geography and environmental management. This paper examines the relationships between tourism and water supply on the Mediterranean island of Mallorca, discussing both the scale of the problem and recent measures to find a solution, particularly the proposed Hydrological Plan for the Balearic Islands (published in 1998/9). Since Mallorca lies in an area likely to be seriously affected by future climate change, its potential effects are discussed and evaluated. One of the most critical problems relates to the coarse spatial resolution of general circulation models for predicting precipitation in an area where precipitation regimes grade steeply from semi-arid to humid temperate. However, it is likely that a continuation of the marked inter-annual and decadal-scale variability in precipitation seen during the recent past probably poses a greater threat to Mallorca’s water supply than the more gradual, progressive change typically predicted to accompany future global warming. Similarly, continued over-exploitation of coastal aquifers will be more critical to water quality issues than the direct impacts of any future sea level rise, although the latter would undoubtedly exacerbate these effects. The conclusion discusses the controversial new ecotasa (‘ecotax’), due to be imposed on Mallorca’s tourist industry in 2002, which is likely to represent only a partial solution to the long-term water supply problem. As the physical, cultural and economic environments of Mallorca are typical of much of the Mediterranean region, the implications of this issue extend well beyond the island’s shores.  相似文献   

Holocene storage of siliciclastic sediment around islands on the middle shelf of the Great Barrier Reef Platform, north-east Australia     

A. D. Heap†  G. R. Dickens†‡  L. K. Stewart†§  K. J. Woolfe† 《Sedimentology》2002,49(3):603-621

Thick sequences of sediment surround the Whitsunday Islands on the middle shelf of the Great Barrier Reef (GBR) Platform. Much of this sediment is siliciclastic material deposited since the sea‐level highstand at around 6·5 ka. This raises a mass balance dilemma because modern terrigenous discharge to the GBR Platform is restricted to the inner shelf. Shallow seismic profiles and sediment samples were collected over 450 km² around the Whitsunday Islands to quantify the mass of siliciclastic sediment for a dynamic model of the shelf. The sea floor and pre‐Holocene surfaces were mapped using 4584 stations along the seismic profiles and a graphical computer program. The total volume of sediment between these two surfaces is 3·67 ± 0·45 × 10⁹ m³. This volume is composed of buried reefs (0·13 ± 0·01 × 10⁹ m³), medium‐ (0·70 ± 0·30 × 10⁹ m³) and fine‐grained shoals (2·84 ± 0·35 × 10⁹ m³). The volume estimates combined with measurements of carbonate concentration, density and porosity indicate that 1850 ± 380 Mt of Holocene siliciclastic sediment surround the Whitsunday Islands in medium‐ (510 ± 225 Mt) and fine‐grained shoals (1340 ± 155 Mt). The total mass of siliciclastic material is 1·7–2·6 times that stored in Cleveland Bay, a similar sized repository on the inner shelf. A simple numerical model has been constructed to explain this large quantity of Holocene siliciclastic sediment. The model results in the appropriate siliciclastic mass next to the Whitsunday Islands by integrating regional shelf processes over time. Unlike the present day, rivers discharged sediment to the middle shelf during the early Holocene. This material was subsequently focused by northward transport into the vicinity of the islands, a geomorphologically complex region that serves as a sediment trap. Although direct riverine inputs to the middle shelf have stopped during the present sea‐level highstand, previously deposited siliciclastic sediment is continually being winnowed from the middle shelf and redeposited next to the Whitsunday Islands. The transport and distribution of siliciclastic sediment on the GBR Platform is thus influenced significantly by storage around islands on the middle shelf.  相似文献   

Procedure of reduction of travel-time curves ofP andS waves at the focal surface     

A. Bottari  B. Federico  M. Pietrafesa  A. Teramo 《Pure and Applied Geophysics》1993,140(4):641-653

A method for the calculation of seismic waves velocities at focal depth is here proposed. A stratified earth model with spherical symmetry and the analytical relationship between the epicentral distance and the travel times of seismic waves are used.This method, applied to the southern Tyrrhenian region and to the Japanese islands, allows to reduce the observed travel times to the focal depth independently of a particular velocity model.  相似文献   

Lateral textural grading in overwash sediments     

Stephen P. Leatherman  Allan T. Williams 《地球表面变化过程与地形》1977,2(4):333-341

Overwash deposits are characterized by horizontally layered laminations. Vertical sequences could be interpreted in terms of individual storm deposits by recognizing time breaks or discontinuities in the stratigraphic section. Results from comparison of channel deposit data for textural grading across the washover fan were inconclusive. Samples taken from individual laminations revealed the true textural grading when traced along a 61 m trench and sampled at designated localities. The overwash deposit was found to become finer in grain size from the apex to the margins of sedimentation in the direction of transport.  相似文献   

海水入侵研究现状与展望   总被引：13，自引：0，他引：13  

李国敏  陈崇希 《地学前缘》1996,3(2):161-168

文中讨论了海水入侵的研究进展：海岸带海水入侵界面或过渡带的模拟，海岛地下淡水透镜体的动力学研究，井孔在界面或过渡带上部抽水所引起的升锥问题以及岸边地下水位动态研究及海平面变化对海水入侵的影响。海水入侵研究经历了从理想假定到合理概化，从室内实验模型、理想模型到数值模型这一过程。数值方法已成为模拟和求解海水入侵问题的最有力工具，海水入侵的过渡带模型成为主要的研究方向。分析了研究中存在的困难，展望了海水入侵研究的未来趋势：边界条件确定，水文地质参数选取，含水层结构估计，海水入侵输运与化学作用的耦合以及海水入侵预报。  相似文献   

大陆下地壳研究的新进展     

吴有林  张琴华 《地质科技情报》1995,14(4):3-7

伴随地球物理、捕虏体岩石学、同位素年代学等方面新资料的不断丰富，大陆深部地质作用及其过程的研究取得了不少新进展。重建下地壳的形成和改造历史，对探讨岩石圈的演化变动具有十分重要的意义。幔源岩浆分异作用、板底垫托作用及局部地壳熔融等在太古代至今下地壳的形成改造和麻粒岩相变质事件中起着关键的作用。活化大陆岛弧的下地壳较为全面地记录了下地壳复杂的演化历史，它是我们研究大陆动力学富有前景的构造区域。  相似文献   

Voices for environmental action? Analyzing narrative in environmental governance networks in the Pacific Islands     

《Global Environmental Change》2017

As climate change pushes against the shorelines of the Pacific Islands, strategies to coalesce power to mitigate for and adapt to environmental degradation become even more relevant. One mechanism employed by the Pacific Islands to overcome conflict is the formation of climate networks that work together to meet the needs of the islands as a region. During this process of networked governance, however, contestations occur between the local and global strategies and knowledges that must be navigated by state and nonstate organizations in these networks in order to achieve their respective aims. In order to gain authority to make decisions and govern on climate issues, these networks employ particular narratives—constructions of the hero, victim, and villain, both human and nonhuman, in the story of climate policy—that both produce and are produced by these local/global contestations. This article explores these issues in the context of the Pacific Island Forum and Pacific Island Development Forum summits leading up to the 2015 Conference of the Parties, and their final climate declarations. Through this investigation, two competing narratives are found—the global technical narrative and the local power narrative. These narratives impacted the deliberations and subsequent climate declarations in these Pacific summits, with both the global technical narrative of the Pacific Island Forum summit and the local power narrative of the Pacific Island Development Forum summit being evident in their final declarations. These narrative constructions have consequences for the representativeness of the decisions made in these networks.  相似文献   

海平面上升对长江口三岛影响的预测研究   总被引：7，自引：2，他引：5  

杨世伦  王兴放 《地理科学》1998,18(6):518-523

根据国际权威机构ＩＰＣＣ １９９０年对２１世纪全球海平面上升的最佳估计值和本区地壳沉降速率以及地面沉降趋势,确定下一世纪长江口相对海平面上升１．０ｍ左右。在此基础上,预测了相对海面上升对海岸工程,交通水利设施湿地损失,洪涝灾害及盐水入侵的影响。  相似文献