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1.
Lithologic control of debris torrent occurrence 总被引：1，自引：0，他引：1
A field-based investigation into the frequency and magnitude of debris torrent systems reveals that lithology controls the spatial and temporal occurrence of debris torrents in the Tsitika Watershed, Vancouver Island, British Columbia. We identified 125 debris torrent systems in the watershed; for half these basins we used dendrochronology, historical air photographs, and field surveys to estimate debris torrent frequency and magnitude for a 30 year period. We find that the volcaniclastic half of the watershed contains more than twice as many debris torrent systems, in which debris torrents occur over seven times more frequently, and the deposits have a higher rate of delivery of sediment to the mainstem river than the intrusive half. Lithologic differences in weathering rates, weathering product grain size, and rock texture can explain the observed differences in debris torrent behaviour. Because debris torrents are the main sediment transport path from hilltop to valley bottom in the region, these results confirm an important lithologic control on regional sediment transport. While the exact numbers are uncertain, we estimate that the sediment flux of volcaniclastic debris torrents in the watershed is five times higher than that of the intrusive debris torrents. 相似文献
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Measures of local relief, regional relief, and slope were calculated from digital elevation models (DEMs) for 50 bedrock units in the Ridge and Valley and Blue Ridge provinces of Tennessee. Each of these measures was normalized and the three were then averaged to produce the erosional resistance index (ERI). Bedrock units with higher ERI values include coarse clastics, intermediate clastics, and metaplutonics. Units with lower values include shales, limestones, limestones plus dolostones, and carbonates plus fine clastics. Dolostones tend to have intermediate values. The calculated ERI values were compared with subjective ratings by a geologist with decades of field experience in east Tennessee. Generally, the agreement between the two ratings was good, the most glaring exception being several shales with improbably high ERI values. These turned out to be thin units cropping out beneath very hard sandstones, allowing them to stand higher and steeper than would otherwise be possible. A systematic method for detecting such erroneously high ERI values is suggested. Inspection of a drainage map superimposed on the geology map shows that in a given area, streams tend to flow on rock units with the lowest ERI values. In addition, statistical analysis shows that bedrock units with the lowest ERI values are, on average, almost three times closer to the nearest stream and six times as likely to have streams flowing on them than are units with highest values. Further, the effect of ERI on stream location is strongest for streams with drainage areas between 1 and 30 km2. Thus, small streams appear to be subject to greater lithologic control than are larger streams. 相似文献
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Yongbo Wang Ulrike Herzschuh Xingqi Liu Oliver Korup Bernhard Diekmann 《Journal of Paleolimnology》2014,51(2):303-312
Lacustrine sediments have been widely used to investigate past climatic and environmental changes on millennial to seasonal time scales. Sedimentary archives of lakes in mountainous regions may also record non-climatic events such as earthquakes. We argue herein that a set of 64 annual laminae couplets reconciles a stratigraphically inconsistent accelerator mass spectrometry (AMS) 14C chronology in a ~4-m-long sediment core from Lake Mengda, in the north-eastern Tibetan Plateau. The laminations suggest the lake was formed by a large landslide, triggered by the 1927 Gulang earthquake (M = 8.0). The lake sediment sequence can be separated into three units based on lithologic, sedimentary, and isotopic characteristics. Starting from the bottom of the sequence, these are: (1) unweathered, coarse, sandy valley-floor deposits or landslide debris that pre-date the lake, (2) landslide-induced, fine-grained soil or reworked landslide debris with a high organic content, and (3) lacustrine sediments with low organic content and laminations. These annual laminations provide a high-resolution record of anthropogenic and environmental changes during the twentieth century, recording enhanced sediment input associated with two phases of construction activities. The high mean sedimentation rates of up to 4.8 mm year?1 underscore the potential for reconstructing such distinct sediment pulses in remote, forested, and seemingly undisturbed mountain catchments. 相似文献
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Integrated acoustic and coring investigation of glacigenic deposits in Spitsbergen fjords 总被引：2，自引：0，他引：2
In many areas of Svalbard, the Neoglacial terminal deposits represent the Holocene glacial maximum. The glaciers began the retreat from their Neoglacial maximum positions around 1900 AD. Based on high resolution acoustic data and sediment cores, sedimentation patterns in four tidewater glacier-influenced inlets of the fjord Isfjorden (Tempelfjorden, Billefjorden, Yoldiabukta and Borebukta), Spitsbergen, were investigated. A model for sedimentation of tidewater glaciers in these High Arctic environments is proposed. Glacigenic deposits occur in proximal and distal basins. The proximal basins comprise morainal ridges and hummocky moraines, bounded by terminal moraines marking the maximum Neoglacial ice extent. The distal basins are characterized by debris lobes and draping stratified glacimarine sediments beyond, and to some extent beneath and above, the lobes. The debris lobe in Tempelfjorden is composed of massive clayey silt with scattered clasts. Distal glacimarine sediments comprise stratified clayey silt with low ice-rafted debris (IRD) content. The average sedimentation rate for the glacimarine sediments in Tempelfjorden is 17 mm/yr for the last ca. 130 years. It is suggested that the stratified sediments in Tempelfjorden are glacimarine varves. The high sedimentation rate and low IRD content are explained by input from rivers, in addition to sedimentation from suspension of glacial meltwater. The debris lobes in Borebukta are composed of massive clayey silt with high clast content. Distal glacimarine sediments in Yoldiabukta comprise clayey silt with high IRD content. The average sedimentation rate for these sediments is 0.6 mm/yr for the last 2300 years. 相似文献
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The objectives of this study were to determine (1) if and where lithologic discontinuities are present in the late Pleistocene Northport drumlins of NW lower Michigan, and (2) the sedimentary processes responsible for the discontinuities. Determining the presence of lithologic discontinuities was achieved through field observations and laboratory analysis. Lithologic discontinuities with varying strengths of expression were found in all upland soils. Upland soils typically have a sedimentologic “cap” dominated by fine sands at the surface with dense, more gravelly till beneath. The occurrence of this cap on upland sites, as well as overlying laminated silts and clays in some inter-drumlin areas, suggests that upland soils in the Northport drumlin field formed from subaqueously reworked glacial till. To accomplish this, the Northport drumlin field must have been inundated by a previously unidentified proglacial lake, after recession of the ice margin during the terminal Pleistocene. The lake may have formed as ice blocks lay in the deep basins to either side of the drumlin field and high morainic uplands spanned the southern edge of the field, which at that time would have been severely isostatically depressed. [Key words: deglaciation, proglacial lakes, paleoenvironmental reconstruction, till, soils, flooding, Great Lakes region.] 相似文献
7.
Vincent Jomelli & Pascal Bertran 《Geografiska Annaler: Series A, Physical Geography》2001,83(1-2):15-28
We analyse the morphology and sedimentology of 25 dirty snow avalanche deposits in the French Alps. The deposits typically have either a snow-ball structure or a massive structure with sliding planes. The snow balls show a longitudinal and a vertical sorting that reflects a sieve effect, similar to that observed in other rapid inertial granular flows. The massive type results from snow compaction when the avalanche is channelled by a gully or when it reaches the distal part of the scree. Velocity decrease and compaction limit the deformation to a zone at the base of the snow mass and cause the formation of distinctive sliding planes. These appear as smooth recrystallised surfaces due to local melt from frictional heating. The flow can be assimilated to a frictional granular flow. No systematic variation of size and shape of the rock debris has been observed along the profiles in both types of deposit. The distribution of rock debris and its fabric suggest that the clasts are transported passively and do not undergo any sorting during displacement. Snow melt after avalanching causes a redistribution of rock debris particularly when the snow thickness is important. This redistribution does not generate new sedimentological characteristics such as enhanced sorting or fabric. 相似文献
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海水中的颗粒有机碳(POC)与生物的生命过程、初级生产力关系密切,是海洋食物链中重要的物质基础和能量来源,因此POC的分布特征可以有效反映其生物地球化学环境。利用中国第33次南极考察期间(2016年12月至2017年1月)在南极半岛邻近海域采集的海水颗粒物样品,研究POC的空间分布特征及其影响因素。结果表明,斯科舍海0—200 m的POC浓度范围为7.44—193.52μg·L~(-1),平均浓度为(48.84±35.09)μg·L~(-1);南斯科舍海岭0—200 m的POC浓度范围为9.13—62.17μg·L~(-1),平均浓度为(29.76±14.12)μg·L~(-1);鲍威尔海盆0—200 m的POC浓度范围为5.87—270.72μg·L~(-1),平均浓度为(48.57±38.92)μg·L~(-1)。表层POC高值出现在斯科舍海区和鲍威尔海盆区,而低值出现在海岭区,与叶绿素a(Chla)的变化趋势一致,与营养盐的变化趋势相反。垂向分布上,各个区域POC平均浓度随深度的增加而减少,鲍威尔海盆和斯科舍海POC最高值都出现在25 m层。分析结果表明光合浮游植物是研究海域POC的主要来源, POC的主要影响因素为温度、水团混合以及海冰环境。斯科舍海与鲍威尔海盆整体非生命POC占比高,可能是由于高磷虾生物量、海冰碎屑以及陆源输入的干扰;南斯科舍海岭整体非生命POC占比低。 相似文献
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Seven soil pits dug in a downhill sequence beneath Martinelli snow patch, Niwot Ridge, Front Range, Colorado, reveal that soils are coarse-grained with only limited evidence of silt translocation. Clay mineralogy within the pits exhibits a widespread and distinct change at a depth of ～15–20 cm. The most common characteristic of this change is a distinct increase in vermiculite in the lower layer, usually accompanied by a decrease in kaolinite and/or smectite. This pattern is interpreted to reflect decreased weathering intensity with depth. Microenvironments beneath the snow patch which exhibit high chemical weathering rates on coarse surficial debris also appear to experience high rates of clay production relative to referenced dry alpine sites, with specific clay mineralogies varying in a fashion commonly found in humid temperate environments. Data generated in this study appear to provide site-specific support for the regionally-developed Synthetic Alpine Slope Model. Spatial variations in eolian additions and meltwater produce complex patterns in chemical weathering of fines beneath large snow patches, although the nature of clay-mineral change is typical of humid, temperate, mid-latitude environments. [Key words: chemical weathering, alpine environments, clay mineralogy, Synthetic Alpine Slope Model.] 相似文献
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Origin and palaeoclimatic significance of the Pleistocene slope covers in the Cracow Upland, southern Poland 总被引：1，自引：0，他引：1
Halina Pawelec 《Geomorphology》2006,74(1-4):50-69
Periglacial slope covers in the southern part of the Cracow Upland, S Poland can be grouped in five genetic categories: slope loess, washed loess, weathered debris, scree deposits, low-density flow deposits, and solifluctites or high-density flow deposits. They differ from each other with respect to their morphological position in relation to the slope, and in lithological characteristics. It was found that successive generations of slope deposits can be distinguished according to their degree of chemical weathering, which can be estimated on the basis of the presence and morphology of limestone clasts, on the content and colour of the colloid clay, and on the Fe2O3 and CaCO3 content of the clay particles.This paper contributes to a discussion on the possibility of palaeoclimate reconstruction based on slope deposits analyses. 相似文献
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Studies on the soil properties of the apparently flat-lying, but salt-affected Banni mudflat region of arid Kachchh in western India revealed the influence of subtle topographic variations on soil texture and nature and distribution of salts. Six master pedons were investigated to an average depth of 150 cm. The pedons on the upper surfaces showed an abundance of fine sand and a gradual impoverishment of silt and clay, as also lesser amounts of salts in the profiles. Pedons on the successively lower surfaces showed more silt and clay contents, as well as higher amounts of salts. The findings helped to identify the areas suitable for pasture development in this vast degraded rangeland, and to suggest some management practices for improvement. 相似文献
12.
Widespread till and moraines record excursions of middle-Pleistocene ice that flowed up-slope into several watersheds of the Valley and Ridge Province along the West Branch of the Susquehanna River. A unique landform assemblage was created by ice-damming and jökulhlaups emanating from high gradient mountain watersheds. This combination of topography formed by multiple eastward-plunging anticlinal ridges, and the upvalley advance of glaciers resulted in an ideal geomorphic condition for the formation of temporary ice-dammed lakes. Extensive low gradient (1°–2° slope) gravel surfaces dominate the mountain front geomorphology in this region and defy simple explanation. The geomorphic circumstances that occurred in tributaries to the West Branch Susquehanna River during middle Pleistocene glaciation are extremely rare and may be unique in the world. Failure of ice dams released sediment-rich water from lakes, entraining cobbles and boulders, and depositing them in elongated debris fans extending up to 9 km downstream from their mountain-front breakout points. Poorly developed imbrication is rare, but occasionally present in matrix-supported sediments resembling debris flow deposits. Clast weathering and soils are consistent with a middle Pleistocene age for the most recent flows, circa the 880-ka paleomagnetic date for glacial lake sediments north of the region on the West Branch Susquehanna River. Post-glacial stream incision has focused along the margins of fan surfaces, resulting in topographic inversion, leaving bouldery jökulhlaup surfaces up to 15 m above Holocene channels. Because of their coarse nature and high water tables, jökulhlaup surfaces are generally forested in contrast to agricultural land use in the valleys and, thus, are readily apparent from orbital imagery. 相似文献
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Major debris-flow deposits occur along the xerothermic valley of the upper Jinsha River. The debris-flow deposits, ranging in thickness from 1 to 20 m, invariably occupy gently inclined piedmont slopes. The sediments are presently deeply dissected by gullies, and the process of mass movement has almost ceased. Detailed textural, stratigraphical, and geochemical studies reveal the formation processes of the debris flows. Seven debris-flow incidents are noted based on the unit combination characteristics of debris-flow deposits. The age estimates of optically stimulated luminescence (OSL) show that the occurrence of debris flows started at around 10.6 kyr BP and weakened until 4.5 kyr BP, corresponding to the obvious strengthened phase of the summer monsoons in the region. The ages of the debris-flow deposits indicate that the occurrence of a mass of debris flows was a response to the intensified summer monsoon in the SE fringe of the Tibetan Plateau since the early Holocene. 相似文献
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云南省苍山十八溪发育十分典型的水石流,流动时表面为高含沙洪水,底部为粗相沙砾和巨石,固液两相离析为非均质两相流。流体具有很大的动能和冲击力,对富绕的苍洱平坝区造成危害。为了治灾除害,保护生态环境,本文对防治目的、治理目标、防治方针与方法,以及实施顺序、程序、方案、技术措施等问题作了阐述。 相似文献
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黄山第四纪泥砾沉积物分形结构特征与沉积环境分析 总被引：13，自引：0，他引：13
黄山第四纪泥砾沉积物粒度组成的分维值介于２．７０８￣２．７５３之间,非常接近古泥石流堆积物粒度组成的典型分维值２．７５。结合沉积特征,表明该类沉积物属第四纪间冰缘环境下的稀性泥石流沉积,其形成过程与季风型冰缘环境有关,是两种环境综合作用的结果。 相似文献
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O.J. Kamalu N.O. Isirimah I.K. Ugwa & J.R. Orimoloye 《Singapore journal of tropical geography》2002,23(2):207-216
The morphological, physical, chemical and pedological properties of eight pedons representative of the four physiographic units in the Meander Belt of the Niger Delta were studied. The soils were classified and the constraints to their agricultural and engineering uses evaluated. The soils were generally poorly drained, having an Aquic moisture regime, mottles and Fe and Mn concretions. They belong to the Entisol and Inceptisol USDA soil taxonomy orders. Soil textures were generally clayey, except for the pedons of the levee crest with sandy loam textures. Bulk density, particle density and total porosity were generally low. Total nitrogen and available phosphorus were also low. The cation exchange capacity (CEC) and base saturation were high. Organic matter was low to moderate. Total elements of the clay were generally high. The soils have poor physical conditions. The high clay content, and the presence of 2:1 lattice clay minerals could account for the deterioration of the major east-west interstate road linking southeast and southwest Nigeria that passes through the area. Optimum use of the soils for agriculture would depend on good land evaluation and efficient soil water management. 相似文献
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The rock-avalanche of February 1995 at Claix (French Alps) 总被引：3，自引：0，他引：3
Pascal Bertran 《Geomorphology》2003,54(3-4):339-346
The sedimentology of a rock-avalanche involving ca. 7·103 m3, that happened on February 1995 at Claix, the French Alps, is analysed here. The talus shows a proximal depression due to the impact of the debris, then a grooved area with few, mainly sandy silt deposits and a downslope accumulation of coarse debris that reaches up to 3 m in thickness. The material underwent mass movement as demonstrated by the steep distal front, the strong fabric strength and the thrust planes. The greatest part of the deposits consists of a clast-supported to partially openwork debris with angular clasts over a sheared matrix-supported basal layer. The largest blocks, often more than 1 m in length, are concentrated at the surface and the front. The overall sedimentological characteristics are similar to those of the small dry grain flows that occur usually on rockfall talus, except for the abundance of fine-grained particles that results from intense cataclasis during flow. It is suggested that the deposits of such medium-scale rock-avalanches, probably not uncommon in seismic regions, may have been confused in previous studies with other slope mechanisms such as debris flow and rockfall. 相似文献