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1.
Diatom assemblages and sulfur content in sediments were analyzed to clarify changes in the sedimentary environment of Kushu Lake, a coastal lake on Rebun Island in Hokkaido, Japan. Salinity variations were assessed by means of a diatom-based index of paleosalinity and the sedimentary sulfur content. This paper discusses the Holocene development of the lake, in relation to Holocene relative sea-level change. For paleoenvironmental interpretation of the lake development, the rationale of the threshold method (Anundsen et al., 1994) was applied.At ca. 8000 yr BP, a coastal embayment (paleo-Kushu Bay) resulted from marine ingression. The threshold elevation at the mouth of the paleo-Kushu Bay kept pace with the rising sea-level, resulting in its enclosure at the culmination of Holocene marine transgression (ca. 6500–5000 yr BP). From predicted relative sea-level at ca. 6000 yr BP for Rebun Island (Nakada et al., 1991), the threshold may have been at least above –3 to –5 m altitude. A freshwater lake environment with strongly anoxic bottom conditions may have occurred from ca. 5500 to 5100 yr BP. After an important episode of marine ingression, the lake was isolated completely from the open sea at ca. 4900 yr BP. The diatom record suggests that the maximum lacustrine extent occurred at ca. 4900–3100 yr BP. Thereafter, water depth decreased at the lake margins.In Kushu Lake, the threshold elevation, due to a build-up of a coastal barrier, prevents us from determining the amplitude of sea-level changes, even though the age of isolation contacts corresponds to periods of regression and climatic deterioration. In spite of isostatic subsidence, the effective protection provided by the well-developed barrier did not allow registration of any relative sea-level fluctuations since its isolation.  相似文献   

2.
Landward retreat (marine transgression) is a common response of coastal systems to rising relative sea level. However, given sufficient sediment supply, the coast may advance seaward. The latter response of gravel barriers has been recorded in parts of southeastern and northwestern Canada, where seaward‐rising sets of beach ridges are observed in areas of Holocene RSL rise. Cape Charles Yorke, northern Baffin Island, is a 5 km long gravel foreland characterized by seaward‐rising beach‐ridge crest elevations. The prograded morphology of the Cape Charles Yorke foreland is a prime example of coastal response to a combination of rising RSL and abundant sediment supply, an unusual and little‐documented pattern in the Canadian Arctic. The main gravel supply to Cape Charles Yorke is likely from eroding bedrock and raised marine deposits southwest of the foreland. Although not the dominant sediment source, the Cape Charles Yorke delta contributed to the formation of the foreland by sheltering it from easterly storm waves and providing an anchor point for the prograding ridges. The truncation of relict ridges by the modern shoreline suggests a recent regime shift from continuous deposition to predominant erosion. The cause and timing of this shift are unknown but could result from a recent dwindling in sediment supply, increased accommodation space, increased wave energy, and/or an accelerated rise of relative sea level.  相似文献   

3.
Four drowned shelf-edge delta complexes, two drowned shelf deltas, three drowned barrier islands, large areas of “hardground”, and fields of bedforms on the mid and outer continental shelf and uppermost slope north of the head of De Soto Canyon, NE Gulf of Mexico were mapped with high-resolution multibeam echosounder. Deltas formed not during the last eustatic low stand, but during one or more interstadials when eustatic sea levels were only 60 to 80 m below present sea level. The barrier islands and deltas must have been cemented prior to rapid falls of eustatic sea level that occurred during global glaciations. Cementation is necessary to have preserved the barrier islands from erosion and subsequent destruction by the rapid sea-level rise during the last deglaciation. The preservation of the relict bathymetry is so good that features that superficially resemble trough blowouts are found in association with one of the relict barrier islands. Asymmetric bedforms on the midshelf in water depths of 50 to 60 m indicate transport directions to the SW but asymmetric bedforms in water depths of the upper slope between 100 and 120 m on the S and SE flanks of the drowned shelf-edge deltas indicate a different current direction, a separate flow that is a continuation of a SW-flowing current that was previously found on the upper slope off NW Florida.  相似文献   

4.
Chesil Beach (Dorset) is one of the most famous coastal landforms on the British coast. The gravel beach is over 18 km long and is separated for much of its length from land by a tidal lagoon known as The Fleet. The beach links the Isle of Portland in the east to the mainland in the west. Despite its iconic status there is little available information on its internal geometry and evolutionary history. Here we present a three-fold model for the evolution of Chesil Beach based on a series of nine ground penetrating radar (GPR) traverses located at three sites along its length at Abbotsbury, Langton Herring and at Ferry Bridge. The GPR traverses reveal a remarkably consistent picture of the internal structure of this barrier beach. The first phase of evolution involves the landward transgression of a small sand and gravel beach which closed upon the coast leading to deposition of freshwater peat between 5 and 7 k yr BP. The second evolutionary phase involves the ‘bulking-out’ of the beach during continued sea level rise, but in the presence of abundant gravel supplied by down-drift erosion of periglacial slope deposits. This episode of growth was associated with a series of washover fans which accumulated on the landward flank of the barrier increasing its breadth and height but without significant landward transgression of the barrier as a whole. The final phase in the evolution of Chesil Beach involves the seaward progradation of the beach crest and upper beach face associated with continued sediment abundance, but during a still-stand or slight fall in relative sea level. This phase may provide further evidence of a slight fall in relative sea level noted elsewhere along the South Coast of Britain and dated to between 1.2 and 2.4 k yr BP. Subsequently the barrier appears to have become largely inactive, except for the reworking of sediment on the beach face during storm events. The case study not only refines the evolutionary picture of Chesil Beach, but illustrates the importance of the subtle interplay between relative sea level and sediment supply in the evolution of a barrier system. In addition, it also illustrates the potential of GPR in resolving the evolutionary history of gravel-rich coastal landforms such as Chesil Beach.  相似文献   

5.
ABSTRACT This study addresses the complex relationship between an evolving fault population and patterns of synrift sedimentation during the earliest stages of extension. We have used 3D seismic and well data to examine the early synrift Tarbert Formation from the Middle–Late Jurassic northern North Sea rift basin. The Tarbert Formation is of variable thickness across the study area, and thickness variations define a number of 1- to 5-km-wide depocentres bounded by normal faults. Seismic reflections diverge towards the bounding faults indicating that the faults were active contemporaneous with the deposition of the formation. Many of these faults became inactive during later Heather Formation times. The preservation of the Tarbert Formation in both footwall and hangingwall locations demonstrates that, during the earliest synrift, the rate of deposition balanced the rate of tectonic subsidence. Local space generated by hangingwall subsidence was superimposed upon accommodation generated due to a regional rise in relative sea-level. In basal Tarbert Formation times, transgression across the prerift coastal plain produced lagoons and bays, which became increasingly marine. During continued transgression, barrier islands moved landward across the drowned bays. In the southern part of our study area, shallow marine sediments are erosionally truncated by fluvial deposition. These fluvial systems were constrained by fault growth monoclines, and flowed parallel to the main faults. We illustrate that stratal architecture and facies distribution of early sedimentation is strongly influenced by the active short-lived faults. Local depocentres adjacent to fault displacement maxima focused channel stacking and allowed the aggradation of thick shoreface successions. These depocentres formed early in the rift phase are not necessarily related to Late Jurassic – Early Cretaceous depocentres developed along the major linked normal fault systems.  相似文献   

6.
A numerical model linking a coral growth algorithm and an algorithm for flexural subsidence reproduces many of the characteristics of drowned foreland basin carbonate platforms. This model successfully matches the observed distribution and drowning age of drowned carbonate platforms in the Huon Gulf, Papua New Guinea, a modern submarine foreland basin. Analysis of equations describing flexural subsidence and eustatic sea-level variations suggest that there are minimum convergence rates and periodicities of sea-level variation required to drown foreland basin carbonate platforms. For convergence rates on the order of a few millimetres per year, sea-level must vary on time-scales of about 105 years in order to induce a rate of relative sea-level rise great enough to drown an otherwise healthy foreland basin carbonate platform.  相似文献   

7.
We report a study of the Holocene coastal sediments of the Hai Phong area of the Bac Bo Plain (also known as the Red River Delta) in northern Vietnam. This is the first attempt to interpret the region's coastal depositional environments in the light of a geological model of Holocene environmental change recognising the interacting roles of Holocene sea-level change, alluvial responses to sea-level fluctuation, and tidal environment sedimentation. The coastal sediments overlie a Pleistocene land surface, and represent the Holocene marine transgression and regression. Prior to c .6000 bp , the sea rose to around or above its present elevation, converting the Pleistocene terrestrial landscape to a Holocene tidal landscape of tidal flat, channel and mangrove environments. Sea-level lowering by c .4000 bp triggered a switch in dominant sedimentary processes, allowing floodplain sediments to be deposited increasingly seawards.  相似文献   

8.
Santa Rosa Island is an 85 km-long, wave-dominated low-lying barrier island situated along the northwestern Florida coast, facing the Gulf of Mexico. The entire island was severely impacted by Ivan, a strong category 3 hurricane that made landfall about 45 km to the west in September of 2004. Ten months later in July of 2005, Dennis, another category 3 hurricane, made landfall about 30 km east of the western tip of the island. Santa Rosa Island is characterized by well-developed but relatively low dunefields, described in this paper as incipient and established dunes, based on the presence of grassy and woody types of vegetation, respectively. The dunes were severely eroded by the two hurricanes. This paper investigates the factors controlling the regional-scale destruction and survival of the dunefields.Dune survival is controlled by: 1) hurricane characteristics, including intensity, duration, and frequency, and 2) morphological parameters including width of the barrier island, height and width of the dunefields, vegetation type, distance of the dunes to the ocean, and continuity of the dunefields. Three processes of dune destruction are described including, from most to least severe, inundation, overwash, and scarping. The interaction of all the above factors determines the different dune responses to the storm impacts. In general, the extensive and densely woody vegetated dunefields near the bay-side shoreline survived the storms, while the discontinuous dunes with grassy vegetation near the Gulf shoreline were almost completely destroyed.  相似文献   

9.
珠江三角洲新石器考古文化与古地理环境   总被引：12，自引：0，他引：12  
黄光庆 《地理学报》1996,51(6):508-517
珠江三角洲新石器时期的贝丘和沙丘类文化属沿海渔业文化带，其产生和发展与全新的世海面及海陆变迁密切相关。贝丘和沙丘类古文化是随６０００ａＢＰ以前的海侵而产生的；其文化的发展和盛衰过程，在时间和空间上与珠江三角洲海陆环境演变序列都十分吻合。  相似文献   

10.
The southern Delmarva Peninsula is located along the middle Atlantic Coastal Plain of the United States. The axial highland of the peninsula formed in four stages of Pleistocene spit progradation. The landward shoreline of the peninsula is on the Chesapeake Bay. The seaside shoreline of the peninsula is on the Atlantic Ocean. The coast of the peninsula is composed of five landscape sections described as a headland, a left-hand spit, a right-hand spit, a wave-dominated barrier island, and tide-dominated barrier islands.Fisherman Island is a barrier island located at the southern end of the southern Delmarva Peninsula. The landscape features on Fisherman Island do not illustrate a direct linkage to (1) the sediment dispersion from the Delaware headland or (2) the influence of local antecedent topography. The island has a bipolar progradational history that is normal to the axis of the southerly sediment dispersion pattern from the Delmarva headlands.During the late Holocene, sea-level rise flooded the low-elevation land at the distal end of the southern Delmarva Peninsula. The submerged area formed a shallow platform in the entrance to the Chesapeake Bay. Two sediment dispersion tracts affected the development of this area. On the ocean side of the peninsula, sediment moved southward along the lower shoreface to the Chesapeake Bay entrance. On the west side of the peninsula, southerly moving bay currents also dispersed sediment to the entrance of the bay. The two tracts converged on the northern side of the bay entrance forming a broad sand shoal. Wave diffraction and refraction around the margins of the shoal “swept” sediment into linear sand bars that migrated back toward the peninsula.By the middle of the 19th century, the fusion of sand bars on the shoal surface produced a permanent nucleus for island development. Wave refraction caused wave crests to “wrap around” the island core producing separate easterly and westerly components of shore aggradation. The westerly aggradational history is recorded in closely spaced sets of beach ridges. The easterly aggradational history is recorded in broadly spaced hammocks.  相似文献   

11.
R.M. Joeckel  G.M. Henebry   《Geomorphology》2008,102(3-4):407-418
The lower Platte River has undergone considerable change in channel and bar characteristics since the mid-1850s in four 20–25 km-long study stretches. The same net effect of historical channel shrinkage that was detected upstream from Grand Island, Nebraska, can also be detected in the lower river but differences in the behaviors of study stretches upstream and downstream from major tributaries are striking. The least relative decrease occurred downstream from the Loup River confluence, and the stretch downstream from the Elkhorn River confluence actually showed an increase in channel area during the 1940s. Bank erosion was also greater downstream of the tributaries between ca. 1860 and 1938/1941, particularly in stretch RG, which showed more lateral migration. The cumulative island area and the ratio of island area to channel area relative to the 1938/1941 baseline data showed comparatively great fluctuations in median island size in both downstream stretches. The erratic behavior of island size distributions over time indicates that large islands were accreted to the banks at different times, and that some small, newly-stabilized islands were episodically “flushed” out of the system. In the upstream stretches the stabilization of mobile bars to create new, small islands had a more consistent impact over time. Channel decrease by the abandonment of large, long-lived anabranches and by the in-place narrowing resulting from island accretion were more prominent in these upstream stretches. Across all of the study area, channel area appears to be stabilizing gradually as the rate of decrease lessens. This trend began earliest in stretch RG in the late 1950s and was accompanied by shifts in the size distributions of stabilized islands in that stretch into the 1960s. Elsewhere, even in the easternmost study stretch, stabilizing was occurring by the late 1960s, the same time frame documented by investigations of the Platte system upstream of the study area. Comprehensive management plans for the lower Platte River should account, at least in theory, for the observed differences in stream behavior upstream and downstream of the major eastern tributaries.  相似文献   

12.
The study aims to estimate the relative contributions of the two drainage basins of the Aliakmon and Axios rivers which, since the Mid-Holocene, have been responsible for building the largest deltaic area in Greece. Sediments from five cores located in the central part of the Thessaloniki Plain have been studied for their environmental changes using paleontological and sedimentological methods. Chronostratigraphical evidence was obtained from 14C AMS dating of marine shells, peat and organic sediment samples. During the Holocene marine transgression, this large coastal plain was a shallow marine bay reaching approx. 35 km inland circa the 4th millennium BC, from which the sea subsequently regressed to the east. Around the middle of the 3rd millennium BC, strong fluvial deposition of Aliakmon, to the east, and of Axios, to the north, occurred and was responsible of a gradual change to lagoonal and limnic environmental conditions. Around the 5th Century BC, a freshwater lake occupied the westernmost part of the plain.Microfaunal identification, together with magnetic susceptibility measurements, and grain-size analysis reveal three main environments of sediment deposition that reflect combinations of both concentrated and dispersed sources of magnetic/source minerals. Using remote sensing and a combination of spectral bands (LANDSAT TM imagery), we identify former fluvial levees and a freshwater lake, and give a spatial interpretation of the rivers' influences in building this deltaic complex. The mechanisms of edification of the plain as well as the roles played by Aliakmon and Axios sedimentation are described.  相似文献   

13.
Low-lying atoll islands appear highly vulnerable to the effects of climate change and extreme natural events. Potentially disastrous effects of future sea-level rise have been inferred in many studies, and the actual impacts of tropical storms on island destruction and formation have been well documented. In contrast, the role of tsunami in the geomorphic development of atoll islands has not been investigated. The Sumatran earthquake of 26 December 2004 generated a tsunami that reached the Maldives 2500 km away, with waves up to 2.5 m high. Observations on the geomorphic changes resulting from the tsunami are detailed here, based on pre-and post-tsunami profile measurements of island, beach and reef topography, and GPS surveys of the planform shape of islands and beaches of 11 uninhabited islands in South Maalhosmadulu atoll, Maldives. Erosional and depositional impacts were observed on all islands and these have been quantified. In general the changes were of a minor nature with a maximum reduction in island area of 9% and average of 3.75%. Rather, the tsunami accentuated predictable seasonal oscillations in shoreline change, including localised erosion reflected in fresh scarps and seepage gullies. Depositional features in the form of sand sheets and sand lobes emplaced on the vegetated island surfaces provide clear evidence that the tsunami waves washed over parts of all the islands. Both erosional scarps and overwash deposits were concentrated at the tsunami-exposed eastern sides of the islands. Impacts on leeward shores were primarily accretionary, in the form of spit and cuspate foreland extension. Whereas the nature and magnitude of intra-and inter-island impacts was variable, an east to west decline in aggregate effects was noted. Detailed consideration of the morphodynamic interaction between the tsunami waves and island morphology, show that this cross-atoll gradient resulted not just from the reduction in tsunami energy as it passed through the atoll, but also from variations in elevation of the encircling island ridge, and the quantity and distribution of sediment in the antecedent beach. A conceptual model identifying the sequence of changes to individual islands supports the observational data and the pattern of geomorphic changes resulting from the tsunami. This model leads to consideration of the longer-term impacts of the tsunami on the future stability of islands. Four scenarios are presented, each of which has a different island-beach sediment budget, and different relaxation time to achieve dynamic equilibrium.  相似文献   

14.
A detailed geomorphologic and morphostratigraphic investigation of raised marine terraces at Cape Cuvier, Western Australia, reveals two morphologically distinct units. A lower, well-developed accretional reef terrace between 3 and 5.5 m above MLWS (mean low-water springs; hereafter denoted as “+”) represents an extended interval of stable sea level. An upper erosional terrace and incipient coralgal rim between + 8.5 to 10.5 m represents a brief sea-level stillstand at this higher elevation. These features suggest the lower and upper terraces developed during discrete sea-level events. In an attempt to better define the timing of emplacement of each marine unit, 20 coral samples collected along vertical and lateral reef growth axis from both terraces were analysed with U-series dating. Unfortunately, all coral samples exhibited elevated δ234Uinitial values, suggesting that pervasive uptake of 234U-enriched uranium and 230Th thorium had occurred. Despite the shortcomings of absolute dating, a succession of events can be resolved though morphostratigraphic relationships. Comparison of the facies relationships, coral growth, and morphostratigraphic features between the lower and upper terraces indicates that an early to mid MIS 5e stillstand at + 3 to 5 m was followed by a late rise to + 8.5 to 10.5 m. This agrees with an emerging global view of MIS 5e sea-level history derived from stable carbonate platforms, rejecting the hypothesis that these higher sea-level benchmarks are an artefact of localized tectonic processes.  相似文献   

15.
As in the past, most Pacific Island people live today along island coasts and subsist largely on foods available both onshore and offshore. On at least two occasions in the 3500 years that Pacific Islands have been settled, sea level changes affected coastal bioproductivity to the extent that island societies were transformed in consequence. Over the past 200 years, sea level has been rising along most Pacific Island coasts causing loss of productive land through direct inundation (flooding), shoreline erosion and groundwater salinization. Responses have been largely uninformed, many unsuccessful. By the year 2100, sea level may be 1.2 m higher than today. Together with other climate‐linked changes and unsustainable human pressures on coastal zones, this will pose huge challenges for livelihoods. There is an urgent need for effective and sustainable adaptation of livelihoods to prepare for future sea level rise in the Pacific Islands region. There are also lessons to be learned from past failures, including the need for adaptive solutions that are environmentally and culturally appropriate, and those which appropriate decision makers are empowered to design and implement. Around the middle of the twenty‐first century, traditional coastal livelihoods are likely to be difficult to sustain, so people in the region will need alternative food production systems. Within the next 20–30 years, it is likely that many coastal settlements will need to be relocated, partly or wholly. There are advantages in anticipating these needs and planning for them sooner rather than later. In many ways, the historical and modern Pacific will end within the next few decades. There will be fundamental irreversible changes in island geography, settlement patterns, subsistence systems, societies and economic development, forced by sea level rise and other factors.  相似文献   

16.
Radiocarbon dating of marsh facies peat and drowned trees along the barrier beaches at the south end of Lake Winnipeg, indicates water levels are presently rising. Lagoonal sediment and associated trees are being buried as the barrier islands move landward in response to rising water levels. Estimates based on radiocarbon dating suggest the water level has been rising 20 cm/century over the last three hundred years. This estimate is consistent with lake level records and models of isostatic uplift which suggest the level of the lake should be rising between 6.7 and 12 cm/century along the south shore. However, additional radiocarbon dates on submerged trees from Observation Point, at the north end of South Basin, and the Spider Islands, near the northern outlet, indicate that at least part of the water-level rise is basin wide. Southward transgression of Lake Winnipeg, throughout the Holocene, is believed to be the result of isostatic tilting of the basin, whereas the recent basin-wide water-level rise is more likely the result of a combination of isostatic tilting and increased precipitation associated with climate change.  相似文献   

17.
The mid-Cretaceous was a time in which rapid vertical carbonate accumulation alternated with intervals of world-wide crisis on carbonate platforms. Next to the well-known mid-Valanginian, mid-Aptian and Cenomanian/Turonian event, the late Albian Rotalipora appennirjica-7.one is a period of severe platform crisis which is reflected differently on different platforms in the Tethys, the Pacific and the Atlantic Ocean. On the Dinaric Platform in western Slovenia (Tethys) karstification and subsequent temporary drowning of parts of the platform is recorded in sediment infillings of a cave system in a reef along the northern edge of the open ocean platform. Biostratigraphic analysis indicates that vertical aggradation, karstification, short-term pelagic influx and subsequent shallow-water carbonate production all took place in the late Albian. Simultaneous, but complete drowning can be observed in the north-west Pacific which is an area where the demise of reefs is most obviously expressed by numerous sunken atolls. New sedimentological and palaeontological data, as well as seabeam and seismic data from several cruises, suggest a dramatic fall of sea level prior to a rise of even higher amplitude in the Rotalipora appenninica-zone. This sea-level rise led to the deposition of a drowning succession and the formation of terminally drowned barrier reefs, rimming the top of many guyots. Karstification and drowning during the same biozone is also recorded on an isolated, shelf-attached platform in the Basco-Cantabrian Basin (North Atlantic) which shows similar cavity systems, infilling sediments and a thin drowning succession. Another example of late Albian platform drowning is the Maracaibo Platform in north-west Venezuela. Thus, carbonate platforms can be used as recorders of high-amplitude sea-level changes, providing quantitative data on magnitude of fluctuations and their nature (relative vs. eustatic). In the case of the appenninica-extnt, they also provide evidence that even during Cretaceous greenhouse climate period(s), dramatic disturbance of climatic equilibrium linked with short-term high-amplitude regressive-transgressive cycle(s) occurred. The reason for this eustatic sea-level fluctuation is yet unclear but could ultimately be triggered by volcanotectonic processes.  相似文献   

18.
The response of a barrier island to an extreme storm depends in part on the surge elevation relative to the height and extent of the foredunes which can exhibit considerable variability alongshore. While it is recognized that alongshore variations in dune height and width direct barrier island response to storm surge, the underlying causes of the alongshore variation remain poorly understood. This study examines the alongshore variation in dune morphology along a 11 km stretch of Santa Rosa Island in northwest Florida and relates the variation in morphology to the response of the island during Hurricane Ivan and historic and storm-related rates of shoreline erosion. The morphology of the foredune and backbarrier dunes was characterized before and after Hurricane Ivan using Empirical Orthogonal Function (EOF) analysis and related through Canonical Correlation Analysis (CCA). The height and extent of the foredune, and the presence and relative location of the backbarrier dunes, varied alongshore at discrete length scales (of ~ 750, 1450 and 4550 m) that are statistically significant at the 95% confidence level. Cospectral analysis suggests that the variation in dune morphology is correlated with transverse ridges on the inner-shelf, the backbarrier cuspate headlands, and the historical and storm-related trends in shoreline change. Sections of the coast with little to no dune development before Hurricane Ivan were observed in the narrowest portions of the island (between headlands), west of the transverse ridges. Overwash penetration tended to be larger in these areas and island breaching was common, leaving the surface close to the watertable and covered by a lag of shell and gravel. In contrast, large foredunes and the backbarrier dunes were observed at the widest sections of the island (the cuspate headlands) and at crest of the transverse ridges. Due to the large dunes and the presence of the backbarrier dunes, these areas experienced less overwash penetration and most of the sediment from the beachface and dunes was deposited within the upper-shoreface. It is argued that this sediment is returned to the beachface through nearshore bar migration following the storm and that the areas with larger foredunes and backbarrier dunes have smaller rates of historical shoreline erosion compared to areas with smaller dunes and greater transfer of sediment to the washover terrace. Since the recovery of the dunes will vary depending on the availability of sediment from the washover and beachface, it is further argued that the alongshore pattern of dune morphology and the response of the island to the next extreme storm is forced by the transverse ridges and island width through alongshore variations in storm surge and overwash gradients respectively. These findings may be particularly important for coastal managers involved in the repair and rebuilding of coastal infrastructure that was damaged or destroyed during Hurricane Ivan.  相似文献   

19.
Dungeness Foreland is a large sand and gravel barrier located in the eastern English Channel that during the last 5000 years has demonstrated remarkable geomorphological resilience in accommodating changes in relative sea-level, storm magnitude and frequency, variations in sediment supply as well as significant changes in back-barrier sedimentation. In this paper we develop a new palaeogeographic model for this depositional complex using a large dataset of recently acquired litho-, bio- and chrono-stratigraphic data. Our analysis shows how, over the last 2000 years, three large tidal inlets have influenced the pattern of back-barrier inundation and sedimentation, and controlled the stability and evolution of the barrier by determining the location of cross-shore sediment and water exchange, thereby moderating sediment supply and its distribution. The sheer size of the foreland has contributed in part to its resilience, with an abundant supply of sediment always available for ready redistribution. A second reason for the landform's resilience is the repeated ability of the tidal inlets to narrow and then close, effectively healing successive breaches by back-barrier sedimentation and ebb- and/or flood-tidal delta development. Humans emerge as key agents of change, especially through the process of reclamation which from the Saxon period onwards has modified the back-barrier tidal prism and promoted repeated episodes of fine-grained sedimentation and channel/inlet infill and closure. Our palaeogeographic reconstructions show that large barriers such as Dungeness Foreland can survive repeated “catastrophic” breaches, especially where tidal inlets are able to assist the recovery process by raising the elevation of the back-barrier area by intertidal sedimentation. This research leads us to reflect on the concept of “coastal resilience” which, we conclude, means little without a clearly defined spatial and temporal framework. At a macro-scale, the structure as a whole entered a phase of recycling and rapid progradation in response to changing sediment budget and coastal dynamics about 2000 years ago. However, at smaller spatial and temporal scales, barrier inlet dynamics have been associated with the initiation, stabilisation and breakdown of individual beaches and complexes of beaches. We therefore envisage multiple scales of “resilience” operating simultaneously across the complex, responding to different forcing agents with particular magnitudes and frequencies.  相似文献   

20.
大长山岛土地利用变化及其土地与海域综合利用探讨   总被引：1，自引：0，他引：1  
当前国内外对土地利用及其变化的研究, 多数是对陆域的城市或有关区域的土地利用及 其变化的研究, 而对海岛土地利用及其变化的研究报道很少。海岛是海中陆地, 由岛陆、岛基、岛 滩和环岛浅海组成, 海岛土地利用及其变化的特征受海陆因素的影响。尤其在海岛的海岸带地 段, 这种影响更为明显, 具体体现在海岸带滩涂土地和浅海水域的利用上。论文对北黄海大长山 岛的土地利用及其变化进行了论述; 分析了大长山岛土地利用特征、土地利用结构随时间变化的 趋势; 同时, 根据我国颁布的《海域使用法》和《物权法》的内容, 对海域与海岛土地的属性以及将 海岛土地与海域利用作为一个系统, 在理论与法律依据上进行了探讨。  相似文献   

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