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1.
论旅游资源中石灰华景观的形态建成过程--以四川九寨沟和贵州黄果树等地石灰华群为例 总被引：6，自引：0，他引：6
在众多风景旅游资源中,石灰华景观以其独特壮丽的形态为世人所瞩目,并引发出一系列对其成因的解释。本文通过对四川九寨沟和贵州黄果树等旅游地区的石灰华景观进行考察和研究,认为,石灰华景观的形态建成过程主要是受生物、地形和水文的共同控制。其中,生物的控制作用处于十分重要或中心地位,生物(蓝藻、绿藻等低等生物)通过与沉积物颗粒紧密结合形成的藻席的成层加积和侧向延伸生长,与地形、水文等因素一起共同引导和控制着石灰华景观的形成和发育规模。文中提出了旅游资源中瀑华和坝华等主要石灰华景观的形态建成过程模式,为石灰华景观旅游资源的科学保护提出理论依据。 相似文献
2.
Zhang Jie Li Shengfeng Zhou Yinkang Du Jinkang Department of Geography Nanjing University Nanjing People''s Republic of China 《地理学报(英文版)》1997,(3)
1.ＩｎｔｒｏｄｕｃｔｉｏｎＲｅｓｅａｒｃｈｏｎｂｉｏｋａｒｓｔｓｔｒｅｔｃｈｆｒｏｍｎｉｎｅｔｅｅｎｔｈｃｅｎｔｕｒｙ,ｙｅｔｏｎｌｙｒｅｃｅｎｔｌｙ,ｍｏｒｅｅｆｆｉｃｉｅｎｔａｎｄｓｙｓｔｅｍａｔｉｃｒｅｓｅａｒｃｈｈａｓｂｅｅｎｐｕｔｆｏｒｗａｒｄｗｉｔｈｔｈｅａｐｐｅａｒａｎｃｅｏｆｒｅｌａｔｅｄｓｐｅｃｉａｌｔｅｒｍｉｎｏｌｏｇｙａｎｄｄｅｔａｉｌｅｄｒｅｖｉｅｗｓ[3,11,30,3638],ａｎｄｉｔｓｅｅｍｓｔｈａｔｔｈｅｒｅｉｓｓｔｉｌｌｌａｃｋｏｆｂｉｏｋａｒｓｔｉｎａｌｐｉｎｅｅｎｖｉｒｏ… 相似文献
3.
《Geomorphology》2006,73(1-2):78-100
Spring-fed streams that deposit tufa (ambient temperature freshwater calcium carbonate deposits) in the tropics of northern Australia are influenced strongly by perennially warm water temperatures, high evaporation rates, and monsoon driven high-magnitude floods. This paper presents an environmental model that will aid interpretation of fossil fluvial tufas throughout monsoonal Australia. In the Barkly karst, northern Australia, tufas form in dam, cascade and pool/waterhole geomorphic environments. Each environment is represented in the morphostratigraphical record by a specific combination of tufa geomorphic units and facies associations. A diverse array of tufa facies is present, including microphytic, larval, calcite raft, macrophytic and allochthonous types.Preservation of particular Barkly karst tufa facies is thought to reflect the strength of monsoonal floods. A strong monsoon is represented by an abundance of flood indicators such as the allochthonous phytoclastic, lithoclastic and intraclastic tufa facies. Conversely, evidence of weak monsoons or a prolonged absence of floods may include oncoids, calcite rafts and thick accumulations of fine carbonate sediments. The history of the Australian monsoon is not fully understood. However, fossil tufa deposits, which record terrestrial climate information, have been preserved throughout northern Australia and hold great potential for reconstructing the region's climate history. Fossil tufa sequences at two Barkly karst sites have been interpreted using the new model. It can be applied to other Barkly karst fossil tufas as well as those in similar environments elsewhere in the world. 相似文献
4.
YUICHI S. HAYAKAWA HIROYUKI OBANAWA YUKINORI MATSUKURA 《Geografiska Annaler: Series A, Physical Geography》2008,90(1):65-74
Post‐eruptive fluvial erosion of welded pyroclastic flow deposits often depends on the recession of waterfalls because of their rapid erosion involved. We examine the recession rate of Shomyo Falls, which consists of Pleistocene welded pyroclastic flow deposits in Tateyama, north‐central Japan. The mean recession rate of the waterfall obtained from lithological and topographical evidences is 0.08‐0.15 m/a for 100000 a. However, the recession rate estimated by means of an empirical equation comprising physical parameters of erosive force and bedrock resistance is 0.006‐0.011 m/a with small uncertainties. The discrepancy between the geology‐based and equation‐based recession rates indicates that some factors, not taken account of in the equation, significantly influence the recession rate. We suggest that a factor in the rapid erosion of the waterfall is a large amount of transported sediment acting as abrasive material, which is supplied from high mountains in the watershed above the waterfall. 相似文献
5.
The rate of recession of Niagara Falls (Horseshoe and American Falls) in northeastern North America has been documented since the 19th century; it shows a decreasing trend from ca. 1 m y− 1 a century ago to ca. 0.1 m y− 1 at present. Reduction of the flow volume in the Niagara River due to diversion into bypassing hydroelectric schemes has often been taken to be the factor responsible, but other factors such as changes in the waterfall shape could play a role and call for a quantitative study. Here, we examine the effect of physical factors on the historically varying recession rates of Niagara Falls, using an empirical equation which has previously been proposed based on a non-dimensional multiparametric model which incorporates flow volume, waterfall shape and bedrock strength. The changes in recession rates of Niagara Falls in the last century are successfully modeled by this empirical equation; these changes are caused by variations in flow volume and lip length. This result supports the validity of the empirical equation for waterfalls in rivers carrying little transported sediment. Our analysis also suggests that the decrease in the recession rate of Horseshoe Falls is related to both artificial reduction in river discharge and natural increase in waterfall lip length, whereas that of American Falls is solely due to the reduction in flow volume. 相似文献
6.
《Geomorphology》2003,49(1-2):45-69
A lahar is a general term for a rapidly flowing mixture of rock debris and water (other than normal streamflow) from a volcano and refers to the moving flow. Located in the populated area of Central Java, the stratovolcano Merapi (2965 m) is prone to lahar generation, due to three main factors: (1) millions of cubic meters of pyroclastic deposits are the product of frequent pyroclastic flows, which have occurred on 2- to 4-year intervals; (2) rainfall intensity is high (often 40 mm in 2 h on average) during the rainy season from November to April; and (3) drainage pattern is very dense. Following the 22 November 1994 eruption of Merapi, 31 rain-triggered lahar events were recorded in the Boyong River between December 1994 and May 1996.On Merapi's slopes, instantaneous sediment concentration at any given time of the lahars varies widely over time and space. Lahars are transient sediment-water flows whose properties are unsteady, so that the sediment load fluctuates during the flow. The boundary between the flow types (debris flow, with sediment concentration >60% volume, or hyperconcentrated flow, with sediment concentration ranges from 20% to 60% volume) may fluctuate within the flow itself. Grain-size distribution, physical composition of sediments, shear stress, yield stress, and water temperature play each a role on this boundary. Natural self-damming and rapid breakout are partly responsible for the sediment variations of the flows.Debris-flow phases at Merapi typically last a few minutes to 10 min, and are often restricted to the lahar front. Debris-flow surges are sometimes preceded and always followed by longer hyperconcentrated flow phases. As a result, mean sediment concentration of the lahars is low, commonly from 20% to 50% volume. Besides, transient normal streamflow phases (sediment concentration <20% volume) can occur between two debris-flow surges.Low sediment load and frequent transient flows in the Merapi channels may result from at least three factors: (1) several breaks-in-slope along the channel increase the deposition rate of sediment, and hinder the bulking capacity of the lahars; (2) source material is mainly coarse debris of “Merapi-type” block-and-ash flows. Consequently, the remobilization of coarse debris is more difficult and the clast deposition is accelerated; (3) variations of rainfall intensity over time and space, common in tropical monsoon rainfall, also influence the sediment load variations of the lahars.Sedimentologic analyses of the lahar deposits in the Boyong River at Merapi encompass clast-supported and matrix-supported debris-flow deposits, hyperconcentrated flow deposits, and streamflow deposits. The stratigraphic succession of massive and stratified beds observed immediately after any given lahar event in the Boyong River indicates that the sediment concentration varies widely over time and space during a single lahar event. Sedimentation rate varies from 3 to 4.5 cm/min during relatively long-lived surges to as much as 20 cm/min during short-lived surges. These results indicate that the sediment load fluctuates during lahar flow, further demonstrating that lahars are transient sediment-water flows with unsteady flow properties. 相似文献
7.
Jan Nyssen Jan Moeyersons Jean Poesen Jozef Deckers Mitiku Haile 《Geomorphology》2003,49(3-4):303-322
Old landslides are prominent features in the landscape around Hagere Selam, Tigray Highlands, Ethiopia. The available evidence suggests their Late Pleistocene to Middle Holocene age and conditions of soil humidity. The affected geological layers, often silicified lacustrine deposits prone to sliding, rest upon or above the water holding Amba Aradam sandstone aquifer.Three examples of present-day (remobilisation of old) mass movements are illustrated and discussed. The aims of the study were to unravel the environmental conditions of the present-day remobilisation of ancient flows, as well as those of first-time landslides. The first two mass movements discussed are slumps, located in areas with vigorous regeneration of (grassy) vegetation. Their activation is thought to be the consequence of an increase in infiltration capacity of the soils under regenerating vegetation. One of these slumps had a horizontal movement of the order of 10–20 m in 1 day.The other case is the remobilisation of the May Ntebteb debris flow below the Amba Aradam sandstone cliff. The debris flow presently creeps downslope at a rate of 3–6 cm year−1. Palynological evidence from tufa shows that the reactivation of the flow started 70 years ago. Shear resistance measurements indicate the danger for continuous or prefailure creep. From the soil mechanics point of view, the reactivation of the debris flow is due to the combination of two factors: (1) the reduction of flow confining pressures as a result of gully incision over the last hundred years, and (2) the increase of seepage pressure as a consequence of the cumulative effect of this incision and the increase in infiltration rates on the lobe since grazing and woodcutting have been prohibited 8 years ago. The role of such exclosures as possible landslide triggers is discussed.From the geomorphological point of view, the ancient movements and their present-day reactivation cannot be compared: the ancient movements led to the development of debris flows, whereas the reactivations relate to the dissection of these mass movement deposits. 相似文献
8.
Well-stratified lacustrine deposits of clay, silt, and marl occur within the rugged mountainous triangle of igneous and metamorphic rocks of Sinai Peninsula, Egypt. These deposits occur only in two sites along Wadi Feiran channel (Feiran and El-Tarfa Oases), where very dense acidic dykes intersect their stream courses. Such dykes played an important role in damming water from torrential rainfall during the humid period to form lakes. The SRTM (90 m) data and high-resolution images (IKONOS) have been utilized to reconstruct the paleolakes in terms of shape, size and water volume. Results show that lake deposits are located where acidic dykes cross narrow channel of high sinuosity. At their former heights, the dykes dammed the surface runoff, thus, three local freshwater paleolakes formed behind them. GIS analysis shows that the largest of these paleolakes was formed in the area of Feiran Oasis. Two other smaller paleolakes were formed at El-Tarfa Oasis due to the presence of two pronounced acidic dykes.These lake deposits were derived mainly from El-Tih Plateau via Wadi El-Akhdar. Another source of these deposits could have been a thin sedimentary cap over the weathered granites northeast of Feiran basin. 相似文献
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10.
Jane C. Marks Roderic Parnell Cody Carter Eric C. Dinger G. Allen Haden 《Geomorphology》2006,77(3-4):299
Travertine deposits of calcium carbonate can dominate channel geomorphology in streams where travertine deposition creates a distinct morphology characterized by travertine terraces, steep waterfalls, and large pools. Algae and microorganisms can facilitate travertine deposition, but how travertine affects material and energy flow in stream ecosystems is less well understood. Nearly a century of flow diversion for hydropower production has decimated the natural travertine formations in Fossil Creek, Arizona. The dam will be decommissioned in 2005. Returning carbonate-rich spring water to the natural stream channel should promote travertine deposition. How will the recovery of travertine affect the ecology of the creek? To address this question, we compared primary production, decomposition, and the abundance and diversity of invertebrates and fish in travertine and riffle/run reaches of Fossil Creek, Arizona. We found that travertine supports higher primary productivity, faster rates of leaf litter decomposition, and higher species richness of the native invertebrate assemblage. Observations from snorkeling in the stream indicate that fish density is also higher in the travertine reach. We postulate that restoring travertine to Fossil Creek will increase stream productivity, rates of litter processing, and energy flow up the food web. Higher aquatic productivity could fundamentally shift the nature of the stream from a sink to a source of energy for the surrounding terrestrial landscape. 相似文献
11.
Surface pressure distributions and 500 millibar flow patterns are identified for summer season days with a moisture stress gradient across the western Great Lakes region that may be related to the location of the prairie-forest ecotone. Results indicate that days with moisture stress gradients are a characteristic feature of the summer climate in the area and that these days are associated with unique, nonrandom groupings of mid-tropospheric flow patterns. SW-NE and W-E stress gradients, those that appear to contribute most to defining and reinforcing the location of the ecotone, occur most frequently, and the modal 500-mb flow direction for these transect groups, an azimuth of 290°, is the same as the mode for the entire population of summer season flow directions. We conclude that the modal mid-tropospheric circulation of the summer season plays a significant role in determining the surface weather conditions that regulate the most common moisture stress patterns within the western Great Lakes region. 相似文献
12.
The final stage of deglaciation of Hudson Bay was a major Holocene catastrophic event marked by the drainage of Lake Agassiz/Ojibway at ~ 8.47 ka cal BP and the rapid collapse of the Laurentide Ice Sheet. Previous work undertaken in the Nastapoka River area (eastern Hudson Bay) demonstrated that during the relative sea level highstand that shortly followed the drainage of the lake, the western margin of the Québec–Labrador ice sector rapidly retreated eastward to reach a stillstand position in a coastal hill range. In this study, an analysis of Landsat 7TM images has allowed a mapping of large-scale glacial landforms (outwash deposits, eskers, flutings, and De Geer and Rogen moraines) between Kuujjuaraapik (SE Hudson Bay) and Puvirnituq (NE Hudson Bay). The key results from this mapping are: i) ice-contact outwash deposits mapped along the entire arc-shaped coastline of the eastern Hudson Bay outline a major ice stillstand phase in the coastal hills that extended at least from Kuujjuaraapik to Inukjuak. The presence of these hills allowed a stabilisation of the ice margin that led to the accumulation of thick and extensive ice-contact submarine fans. ii) The position of these deposits on the down ice side (west) of large sets of flutings indicates an important phase of sediment delivery by a rapid ice flow phase toward a marine-based ice margin. iii) A second system of outwash deposits observed farther inland indicates a subsequent phase of stabilisation of the ice margin during its retreat toward central Québec–Labrador. 相似文献
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A coarse surface layer can help to limit bedload transport rates in channels with cobble and gravel beds. In these systems, periodic boulder-sized clasts often exist with small deposits of fine material in the lee of these large bed elements. A combined field and flume study was conducted to investigate the potential impact of lee deposits with distinctly finer sediment-sizes behind boulders on bedload transport rates. Detailed sediment characterizations were performed on surface, subsurface, and lee sediments in two coarse-bedded Connecticut channels. Bedload measurements also were conducted in a series of flows that approached the bankfull level in these two systems to determine transport rates and the size distribution of bedload material. A 6-m long, 0.5-m wide flume was used to model these systems with fine sediment passing over a fixed bed of sediment particles with uniform-sized, large bed elements. Sediment distributions of the lee deposits in the two Connecticut channels indicate that lee deposits may be produced from winnowing of sediments from the surface layer. Lee deposits also exhibit sediment distributions similar to bedload sediment distributions from low to near-bankfull flow in one of the two channels. Bedload sediments in the second channel were finer than lee deposits, presumably from selective entrainment of fines. Flume experiments demonstrate that bedload transport rates are lower for periods of steady flow relative to periods that include either an increase or decrease in discharge. The results show that lee sediments establish a metastable deposit behind each obstruction for a given discharge. Either increases or decreases in discharge disrupt this temporary stability and increase sediment delivery to the main flow. The study suggests that the influence of the rate of change in discharge may be as important as the absolute magnitude of discharge on sediment transport rates at moderate and low discharges in sediment-limited systems with large bed elements. 相似文献
15.
Brujas Cave, in the Southern Andean Range, is a well-known endokarstic site in Argentina. However, the origin and evolution of this cave system are poorly known. Based on morphological cave features as well as characteristics of cave deposits, we propose a meteogene drawdown cave genesis, including a change from phreatic to vadose conditions related to the high rate of fluvial downcutting in the area. During the vadose period, various cave-related deposits, including authogenic calcite and gypsum speleothems, allogenic volcanic ash and external tufas were deposited. Gypsum crusts are the oldest cave deposits identified (90.2–64.3 ky BP). Their origin, deduced from isotopic characteristics (∂34S=9.6‰), is related to the oxidation of pyrite contained in the Jurassic limestone bedrock as well as the dissolution of overlying Jurassic–Triassic evaporite formations. Gypsum crust deposition is associated with evaporation of water flowing and seeping into the cave during arid environmental conditions. Calcite deposits precipitated from flowing water under equilibrium conditions represent the main speleothem growth period (67.6–34 ky BP in age). Their stable isotope values (∂13C=−3‰ to −5‰ and ∂18O=−9‰ to −11‰) may indicate slightly humid and warm conditions related to the regional Minchin lacustrine phase and global oxygen isotope stage 3. Following this stage, a seismic event is evidenced by accumulations of broken stalactites. Seepage calcite speleothems covering cave walls were deposited under disequilibrium conditions by evaporation, probably during Holocene time. Finally, another more recent gypsum deposition period represented by gypsum balls has been differentiated. Micromorphological as well as isotopic (∂34S=5.6‰) data indicate that these gypsum forms are related to cyclic processes (solution–deposition) from water seeping into the cave under arid conditions. In addition, intense volcanic activity in the area during Holocene time is deduced from allogenic volcanic ash and lapilli located mainly at the entrance cave. At present, limited hydrological activity is observed in the cave and small tufa deposits at karstic discharge points are evidenced. We conclude that the geomorphological evolution of Brujas Cave was controlled by climatic changes (wet and dry stages) under semiarid environmental conditions in a very active tectonic and volcanic setting during Late Quaternary time. 相似文献
16.
Kelin Wang Garth van der Kamp & Earl E. Davis 《Geophysical Journal International》1999,139(3):763-768
Tidal loading causes fluid flow through permeable seafloor and between regions of contrasting elastic properties or porosity within subsea formations. We examine theoretically the dissipation of energy by these flows and its global significance as a mechanism for tidal energy dissipation. Expressions are given for energy dissipation rates in layered formations due to vertical flow caused by tidal loading, but the results can be used to constrain dissipation by other flow patterns. We consider flow near the seafloor, in gas-bearing sediments, and in highly fractured permeable igneous crust. Energy dissipation by the first two mechanisms is negligibly small globally, although it may be locally significant under extreme conditions. Under favourable conditions, flow in fractured crust may have greater energy dissipation, but the total amount is limited by the thickness of the permeable layer. Based on our current understanding of subsea hydrogeology, tidally induced flow in subsea formations appears to make little contribution to the observed global tidal energy dissipation. 相似文献
17.
There are a number of serious problems connected with building and repairing water-retaining elements in embankment dams in cold regions.
One of them is the difficulty in finding inexpensive clay materials with the necessary structural properties and using them in the
winter. Another is the cracks that appear in the upper part of a dam when the core freezes to the banks, and leakage along the cracks threatens
to destroy the dam. Still another is the process of erosion at the bottom of the core which may occur through fissures in the rock foundation
of a dam and in transport constructions. Also, the behaviour of water-retaining elements during earthquakes is unreliable. All of these
problems can be solved by using ice- and cryogel-soil composites created by cryotropic gel formation (CGF). Our laboratory investigations
demonstrate that the materials proposed for water-retaining elements have the necessary permeable, plastic, thermophysical, and strength
properties to solve all of these problems. Certain constructions of water-retaining elements which may prove to be both safe and
cost-effective are proposed. However, these ice- and cryogel-soil composites need to be field-validated before they are used in dams and
transport structures in cold regions. 相似文献
18.
Ogbaghebriel Berakhi L. Brancaccio G. Calderoni M. Coltorti F. Dramis Mohammed M. Umer 《Geomorphology》1998,23(2-4)
This paper presents a geomorphologic–stratigraphic analysis of a travertine dammed lacustrine–swampy sedimentary sequence, composed of clay, peaty layers and phytoclastic travertine sands, deeply incised by the Mai Maikden river, on the Highlands of Tigray (Northern Ethiopia). Radiocarbon datings of peaty deposits allow us to establish that the travertine dams have developed at least between 7310±90 yr B.P. and 5160±80 yr B.P. In the upper part of the sequence, palaeochannels filled with travertine and limestone coarse gravels and blocks, indicate the activation of concentrated erosion on the surrounding slopes. Later, both the travertine dam and the lacustrine–swampy deposits were buried by alluvial and colluvial sediments, still mixed with large amounts of organic matter, testifying to generalized slope erosion processes. The end of travertine deposition may be connected with a progressive reduction of vegetation cover and the subsequent decrease of CO2 in groundwater. The occurrence of the latter phenomena may be related to the onset of drier climatic conditions even though the finding of a large prehistoric settlement in the area, also indicates some influence of human impact. 相似文献
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20.
Relict eolian dunes on the Georgia Coastal Plain line the north and east sides of many SE-trending streams and contain important paleoenvironmental information. A detailed analysis of four dune fields characterizes dune geomorphology, stratigraphy, sedimentology and soils. Georgia's inland dunes range from parabolic to infilled parabolic to irregular in form, typically merge to form long chains that parallel source streams and can occur as distinct bands. Typically, the dunes are composed of >95% quartz sand grains, with more than half the sand falling in the medium sand fraction. Dunes overlie flood plain and pointbar sands, backswamp and peat deposits, fluvial terraces and other dunes. In places, organic deposits occur on top of dunes. Cross-bedding is observable in dunes more than about 4 m thick and indicates eastward dune migration. Paleosols found within some dunes indicate Holocene reworking. Conditions favoring dune formation likely included at least seasonal aridity. Postdepositional modification of the dunes includes a smoothing of the dune surface, a clay increase in the C horizon, spodic horizon development, bioturbation, removal of weatherable minerals and fluvial incision. 相似文献