川西北高原地貌垂直地带性及山地灾害对南水北调西线工程的影响

川西北高原地貌垂直地带性明显:现在流水地貌带海拔高度<3800m;冰缘地貌带为3800⁴200m;冰川地貌带>4200m;相应的主导地貌过程分别是流水侵蚀、冻融侵蚀和冰川侵蚀。川西北高原是大面积构造隆升背景下冻融侵蚀形成的夷平地貌,花岗岩和石灰岩等结晶岩抗寒冻风化能力强,三叠系砂板岩,抗寒冻风化能力差,前者可以形成冰川发育的高山,后者为融冻地貌等发育的丘状起伏的高原面。南水北调西线一期工程主要位于流水地貌带与冰缘地貌带的交界地带,滑坡、崩塌、融冻土流是工程沿线的主要斜坡灾害,规模多为中小型。工程沿线地区泥石流沟数量多、规模小,但流水地貌带内的部分沟谷可能有大型泥石流发生。融冻土流是该区河流泥沙的主要来源,侵蚀产沙对水库淤积的影响应引起重视。冰缘地貌和流水地貌的交错带部位,地貌过程对气候变化的响应相当敏感。     

The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia

The role of post-Little Ice Age (LIA) Neoglacial retreat on landslide activity is investigated in 19 alpine basins along the upper Lillooet River Valley, British Columbia. We examine how Neoglacial scouring and glacial recession have modified hillslope form and slope stability, and construct a decision-making flowchart to identify landslide hazards associated with glacial retreat. This work is based on field mapping, GIS analysis, statistical associations between landslides and terrain attributes, and a comparison between Neoglaciated and non-Neoglaciated terrain within each basin.The bedrock landslide response to glacial retreat varies appreciably according to lithology and the extent of glacial scour below the LIA trimline. Valleys carved in weak Quaternary volcanics show significant erosional oversteepening and contain deep-seated slope movement features, active rock fall, rock slides, and rock avalanches near glacial trimlines. Basins in stronger granitic rock rarely show increased bedrock instability resulting from post-LIA retreat, except for shallow-seated rock slides along some trimlines and failures on previously unstable slopes. In surficial materials, landslides associated with post-LIA retreat originate in till or colluvium, as debris slides or debris avalanches, and are concentrated along lateral moraines or glacial trimlines.Significant spatial association was also observed between recent catastrophic failures, gravitational slope deformation, and slopes that were oversteepened then debuttressed by glacial erosion. Eight out of nine catastrophic rock slope failures occurred just above glacial trimlines and all occurred in areas with a previous history of deep-seated gravitational slope movement, implying that this type of deformation is a precursor to catastrophic detachment.     

Geological controls on Pleistocene glaciation and cirque form in Greece

Limestone and ophiolite rocks are common across the eastern Mediterranean and many of the highest mountains are formed in these rock types. In northwest Greece, Pleistocene glacial erosion was much more effective on limestone terrain where pronounced glacial incision and subglacial glacio-karst processes produced locally-complex topography. This enabled Pleistocene glaciers to form on a range of slope orientations in contrast to ophiolite terrains, where glaciers were strongly controlled by aspect. On limestone terrains, the largest ice masses formed on south-facing slopes, whereas in neighbouring higher mountains formed in ophiolite, glaciers were much more restricted and predominantly formed on north- and east-facing slopes.     

Quantifying the erosional impact of the Fennoscandian ice sheet in the Torneträsk–Narvik corridor, northern Sweden, based on cosmogenic radionuclide data

Despite spectacular landform evidence of a dominant role for glacial action in shaping landscapes under former northern hemisphere ice sheets, there is little quantitative evidence for rates and patterns of erosion associated with specific glaciations. Here we use cosmogenic nuclide data to assess rates of subglacial erosion underneath the Fennoscandian ice sheet. By testing whether there are remnant nuclide concentrations in samples taken from sites that include both relict areas and features and landscapes typically associated with vigorous glacial erosion, we can constrain the level and pattern of modification that resulted from the last glaciation. Cosmogenic ¹⁰Be and ³⁶Cl data from the Torneträsk region confirm the temporal and spatial variability of glacial erosion suggested by geomorphological mapping. At some sites, glacial erosion estimates in what appear to be heavily scoured areas indicate erosion of only c. 2 ± 0.4 m of bedrock, based on cosmogenic nuclide inheritance. This implies that the generation of severely scoured terrain in this study area required multiple glaciations. The overall modification produced by ice sheets along glacial corridors may be more restricted than previously thought, or may have occurred preferentially during earlier Quaternary glacial periods.     

Quantifying the erosional impact of the Fennoscandian ice sheet in the Torneträsk–Narvik corridor, northern Sweden, based on cosmogenic radionuclide data

Despite spectacular landform evidence of a dominant role for glacial action in shaping landscapes under former northern hemisphere ice sheets, there is little quantitative evidence for rates and patterns of erosion associated with specific glaciations. Here we use cosmogenic nuclide data to assess rates of subglacial erosion underneath the Fennoscandian ice sheet. By testing whether there are remnant nuclide concentrations in samples taken from sites that include both relict areas and features and landscapes typically associated with vigorous glacial erosion, we can constrain the level and pattern of modification that resulted from the last glaciation. Cosmogenic ¹⁰Be and ³⁶Cl data from the Torneträsk region confirm the temporal and spatial variability of glacial erosion suggested by geomorphological mapping. At some sites, glacial erosion estimates in what appear to be heavily scoured areas indicate erosion of only c. 2 ± 0.4 m of bedrock, based on cosmogenic nuclide inheritance. This implies that the generation of severely scoured terrain in this study area required multiple glaciations. The overall modification produced by ice sheets along glacial corridors may be more restricted than previously thought, or may have occurred preferentially during earlier Quaternary glacial periods.     

The Rainstorm of August 1998 in the Abisko Area, Northern Sweden: Preliminary Report on Observations of Erosion and Sediment Transport

Several rainstorms with strong erosional effects have been recorded in Scandinavia during recent decades. The erosion occurs by the release of rapid mass movements on mountain slopes or through fluvial incision and bank collapse along streams and rivers. Various factors, such as terrain characteristics and seasonal timing of the rainstorm event, are thought to favour the predominance of either of the two types of erosion for particular events. A new example of this variable impact of rainstorms is briefly described, and related research issues are outlined.     

Geomorphology of subglacial volcanoes in the Azas Plateau, the Tuva Republic, Russia

The Azas Plateau volcanic field is located in the Tuva Republic of the Russian Federation. The compositions of the Azas Plateau volcanics include low-viscosity trachybasalt and basanite. Volcanic edifices of Middle-Late Pleistocene age are widely distributed in the southeastern part of the volcanic field. There are subglacial volcanoes among the volcanic edifices, and their formation coincided with extensive ancient glaciations in the region. The dominant subglacial volcanoes in the area are tuyas. The general shapes of the tuyas (flat-tops with steep sides) are due to eruptions into meltwater lakes and confinement of ice walls, and effusive subaerial eruptions of basaltic lavas. There are also non-flat-topped subglacial volcanoes and at least one subaerial volcanic edifice in the area. Degradation appears to have modified the primary shapes of the tuya edifices, and such processes seem to include failures of over-steepened slopes, gully formation due to stream runoff and debris flows, cirque/valley glaciation, and modification by rock glaciers. The estimated thicknesses of the ice sheets covering the subglacial volcanoes during their eruptions range 300–600 m on average.     

Geomorphological assessment of sites and impoundments for the long term containment of Uranium mill tailings in the Alligator Rivers region

This paper presents a program of current and future research into those geomorphological processes likely to affect the long term containment of uranium mill tailings in the Alligator Rivers Region of the Northern Territory. Research is directed at three main areas: (1) identification of geomorphic hazards at proposed impoundment sites; (2) determination of erosion rates on impoundment slopes; and (3) prediction of patterns of fluvial dispersal of released tailings. Each necessitates consideration of present and future geomorphic processes.     

Long-term landscape development of the Coloradofjella plateau, central Spitsbergen, Svalbard

The development and age of the present geomorphology and superficial material of the Coloradofjella plateau, Spitsbergen, have been investigated through field surveying and laboratory sediment analyses. The focus was specifically on the role of glacial erosion and periglacial processes. The summit plain is deeply incised with large V-shaped valleys. Extensive networks of ice wedge polygons indicate that the fine-grained regolith is at least a few metres thick. An abundance of coarse-grained gabbroid erratics, clearly derived from sources further to the east, are distributed over parts of the summit plain. A vertical-walled dolerite dyke protruding up to 4 m above the adjacent surface shows no sign of glacial erosion. Our findings confirm that the present bedrock geomorphology and regolith in the summit plain survived at least the Late Weichselian glaciation. This is best explained by the ice sheet having been cold-based throughout its existence on the summit plain. Cold-based conditions imply that permafrost survived the last glacial cover. Based on the geomorphic evidence and estimates of Late Cenozoic erosion, we suggest that the present summit plains roughly represent the remains of a preglacial surface.     

Spatial variation of erosion in a small,glaciated basin in the Teton Range,Wyoming, based on detrital apatite (U‐Th)/He thermochronology

Evolution of mountain landscapes is controlled by dynamic interactions between erosional processes that vary in efficiency over altitudinal domains. Evaluation of spatial and temporal variations of individual erosion processes can augment our understanding of factors controlling relief and geomorphic development of alpine settings. This study tests the application of detrital apatite (U‐Th)/He thermochronology (AHe) to evaluate variable erosion in small, geologically complex catchments. Detrital grains from glacial and fluvial sediment in a single basin were dated and compared with a bedrock derived age‐elevation relationship to estimate spatial variation in erosion over different climate conditions in the Teton Range, Wyoming. Controls and pitfalls related to apatite quality and yield were fully evaluated to assess this technique. Probability density functions comparing detrital age distributions identify variations in erosional patterns between glacial and fluvial systems and provide insight into how glacial, fluvial, and hillslope processes interact. Similar age distributions representing erosion patterns during glacial and interglacial times suggest the basin may be approaching steady‐state. This also implies that glaciers are limited and no longer act as buzzsaws or produce relief. However, subtle differences in erosional efficiency do exist. The high frequency of apatite cooling ages from high altitudes represents either rapid denudation of peaks and ridges by mass wasting or an artifact of sample quality. A gap in detrital ages near the mean age, or mid‐altitude, indicates the fluvial system is presently transport limited by overwhelming talus deposits. This study confirms that sediment sources can be traced in small basins with detrital AHe dating. It also demonstrates that careful consideration of mineral yield and quality is required, and uniform erosion assumptions needed to extract basin thermal history from detrital ages are not always valid.     

The failure mechanism of a Late Glacial Sturzstrom in the Subalpine Molasse (Leckner Valley, Vorarlberg, Austria)

A number of prehistoric landslides and rock avalanches occurred in the folded and faulted section of the Molasse Zone in Vorarlberg, Austria. Some developed into a Sturzstrom, defined as a ‘rapidly moving fluidised mass movement of large volumes of rock, derived from the disintegration of a falling rock mass, that spread under the influence of gravity’. Their impact on the landscape usually is related to obstruction of rivers and valleys.In this paper, we analyse the geomorphology and the failure mechanism of a relative small ‘Sturzstrom’. The failure mechanism can be described as a ‘buckling failure’. The morphological situation indicates that failure took place after local deglaciation by the end of the Upper Würm. The period of failure coincides with glacial and ice-marginal remnants, which developed between 15.000 and 14.600 BP. The lithological sequence and rock structure, as well as the impact of the processes related to the former glacial environment, were major causal conditions. The rock sequence consists of conglomerates, sandstone layers, and marls. Next to glacial scouring, which increased the inclination of the valley slopes, the effect of late-glacial unloading and postglacial processes, such as weathering and fluvial erosion, subsequently weakened the mass rock fabric until failure occurred.Discontinuity orientation measurements, geostructural and geomechanical conditions, and the former hydrological and geomorphological conditions support bucklings failure. In fact, three-hinge buckling may have occurred. The frontal section of the Sturzstrom consists mainly of large conglomerate blocks, averaging 1.5 m³ in volume, although megablocks, reaching of up to 4000 m³, are present as well. The volume of the entire Sturzstrom equals approximately 10×10⁷ m³. Present activity is only restricted to minor rock falls derived from the conglomerates and mudflows originating from the marl layers.     

Allometric development of glacial cirque form: Geological, relief and regional effects on the cirques of Wales

Headward and downward erosion near glacier sources, at rates exceeding fluvial erosion, is important in recent discussions of orogen development and the limits to relief. This relates to a long history of debate on how the form of glacial cirques develops, which can be advanced by relating shape to size in large data sets. For 260 cirques in Wales, this confirms different rates of enlargement in the three dimensions: faster in length than in width, and slower in vertical dimension whether expressed as overall height range, axial height range or wall height. Maximum gradient, plan closure and number of cols increase with overall size. This allometric development applies over different cirque types, regions and rock types. Headwall retreat, often by collapse following glacial erosion at the base, is faster than downward erosion. Welsh cirques form a scale-specific population and, as in other regions, size variables follow Gaussian distributions on a logarithmic scale. As in England, width commonly exceeds length. Vertical dimensions correlate with length more than with width. Cirque form varies with geology, but also with relief as both vary between mountain groups. The main contrast is between larger, better-developed cirques and higher relief on volcanic rocks in the north-west, and smaller, less-developed cirques and lower relief on sedimentary rocks in the south.     

Morphology, distribution and formation of relict marginal moraines in the Swedish mountains

Relict marginal moraines are commonly used landforms in palaeoglaciological reconstructions. In the Swedish mountains, a large number of relict marginal moraines of variable morphology and origin occur. In this study, we have mapped 234 relict marginal moraines distributed all along the Swedish mountains and classified them into four morphological classes: cirque‐and‐valley moraines, valley‐side moraines, complex moraines and cross‐valley moraines. Of these, 46 moraines have been reclassified or are here mapped for the first time. A vast majority of the relict moraines are shown to have formed during deglaciation of an ice‐sheet, rather than by local mountain glaciers as suggested in earlier studies. The relict marginal moraines generally indicate that deglaciation throughout the mountains was characterised by a retreating ice‐sheet, successively damming glacial lakes, and downwasting around mountains. The general lack of moraines indicating valley and cirque glaciers during deglaciation suggests that climatic conditions were unfavourable for local glaciation during the last phase of the Weichselian. This interpretation contrasts with some earlier studies that have reconstructed the formation of local glaciers in the higher parts of the Swedish mountains during deglaciation.     

Quantitative geomorphological analysis of drumlins in the Peterborough drumlin field,Ontario, Canada

Drumlins are enigmatic subglacial landforms that have been interpreted to form by a number of processes, including incremental accumulation of till, erosion of previously deposited sediment, catastrophic meltwater floods, and sediment deformation. However, relatively little is known about the controls on drumlin formation, such as spatially variable glacial processes or substrate characteristics, and how these controls may be identified from variations in drumlin morphology within a single drumlin field. This paper explores a computational method that allows identification of drumlins and extraction of their morphological characteristics from existing topographic digital data for a portion of the Peterborough drumlin field in Ontario, Canada. Spatial and non‐spatial analysis of the form and distribution of drumlins across the study area identifies drumlin characteristics such as size, elongation ratio, symmetry and long axis orientation and shows that drumlins are not randomly distributed across the region and their form characteristics have distinct regional trends. Kernel density analysis is used to identify the regional trends in drumlin characteristics. Factors that appear to influence the form and distribution of drumlins in the study area include sediment thickness, length of time beneath the ice, ice velocity and direction of ice movement. The distribution of particularly well developed asymmetric and elongate drumlins coincides with the location of a broad bedrock low and is interpreted to identify the former location of a fast‐flowing ice stream.     

Simulating the development of Martian highland landscapes through the interaction of impact cratering, fluvial erosion, and variable hydrologic forcing

On the highlands of Mars early in the history of the planet precipitation-driven fluvial erosion competed with ongoing impact cratering. This disruption, and the multiple enclosed basins produced by impacts, is partially responsible for a long debate concerning the processes and effectiveness of fluvial erosion. The role of fluvial erosion in sculpting the early Martian landscape is explored here using a simulation model that incorporates formation of impact craters, erosion by fluvial and slope processes, deposition in basins, and flow routing through depressions. Under assumed arid hydrologic conditions, enclosed basins created by cratering do not overflow, drainage networks are short, and fluvial bajadas infill crater basins with sediment supplied from erosion of interior crater slopes and, occasionally from adjacent steep slopes. Even under arid conditions adjacent crater basins can become integrated into larger basins through lateral erosion of crater rims or by rim burial by sediment infilling. Fluvial erosion on early Mars was sufficient to infill craters of 10 km or more in diameter with 500–1500 m of sediment. When the amount of runoff relative to evaporation is assumed to be larger, enclosed basins overflow and deeply incised valleys interconnect basins. Examples of such overflow and interconnection on the Martian highlands suggest an active hydrological cycle on early Mars, at least episodically. When fluvial erosion and cratering occur together, the drainage network is often disrupted and fragmented, but it reintegrates quickly from smaller impacts. Even when rates of impact are high, a subtle fluvial signature is retained on the landscape as broad, smooth intercrater plains that feature craters with variable amounts of infilling and rim erosion, including nearly buried “ghost” craters. The widespread occurrence of such intercrater plains on Mars suggests a strong fluvial imprint on the landscape despite the absence of deep, integrated valley networks. Indisputable deltas and alluvial fans are rare in the crater basins on Mars, in part because of subsequent destruction of surficial fluvial features by impact gardening and eolian processes. Simulations, however, suggest that temporally-varying lake levels and a high percentage of suspended to bedload supplied to the basins could also result in poor definition of fan–delta complexes.     

Slope basins, headless canyons, and submarine palaeoseismology of the Cascadia accretionary complex

A combination of geomorphological, seismic reflection and geotechnical data constrains this study of sediment erosion and deposition at the toe of the Cascadia accretionary prism. We conducted a series of ALVIN dives in a region south of Astoria Canyon to examine the interrelationship of fluid flow and slope failure in a series of headless submarine canyons. Elevated head gradients at the inflection point of canyons have been inferred to assist in localized failures that feed sediment into a closed slope basin. Measured head gradients are an order of magnitude too low to cause seepage-induced slope failure alone; we therefore propose transient slope failure mechanisms. Intercanyon slopes are uniformly unscarred and smooth, although consolidation tests indicate that up to several metres of material may have been removed. A sheet-like failure would remove sediment uniformly, preserving the observed smooth intercanyon slope. Earthquake-induced liquefaction is a likely trigger for this type of sheet failure as the slope is too steep and short for sediment flow to organize itself into channels. Bathymetric and seismic reflection data suggest sediment in a trench slope basin between the second and third ridges from the prism's deformation is derived locally. A comparison of the amounts of material removed from the slopes and that in the basin shows that the amount of material removed from the slopes may slightly exceed the amount of material in the basin, implying that a small amount of sediment has escaped the basin, perhaps when the second ridge was too low to form a sufficient dam, or through a gap in the second ridge to the south. Regardless, almost 80% of the material shed off the slopes around the basin is deposited locally, whereas the remaining 20% is redeposited on the incoming section and will be re-accreted.
     

Glacial erosion and geomorphology in the northwest Sierra Nevada, CA

Pleistocene glacial erosion left a strong topographic imprint in the northwestern Sierra Nevada at many scales, yet the specific landforms and the processes that created them have not been previously documented in the region. In contrast, glaciation in the southern and central Sierra was extensively studied and by the end of the 19th century was among the best understood examples of alpine glaciation outside of the European Alps. This study describes glacially eroded features in the northwest Sierra and presents inferred linkages between erosional forms and Pleistocene glacial processes. Many relationships corroborate theoretical geomorphic principles. These include the occurrence of whalebacks in deep ice positions, roches moutonnées under thin ice, and occurrence of P-forms in low topographic positions where high subglacial meltwater pressures were likely. Some of the landforms described here have not previously been noted in the Sierra, including a large crag and tail eroded by shallow ice and erosional benches high on valley walls thought to be cut by ice-marginal channels.     

Glacial and palaeoenvironmental history of the Cape Chelyuskin area, Arctic Russia

Quaternary glacial stratigraphy and relative sea-level changes reveal at least two glacial expansions over the Chelyuskin Peninsula, bordering the Kara Sea at about 77°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences mapped to altitudes of at least up to ca. 80 m a.s.l. Chronological control is provided by accelerator mass spectrometry ¹⁴C dating, electron-spin resonance and optically stimulated luminescence geochronology. Major glaciations, followed by deglaciation and marine inundation, occurred during marine oxygen isotope stages 6–5e (MIS 6–5e) and stages MIS 5d–5c. These glacial sediments overlie marine sediments of Pliocene age, which are draped by fluvial sediment of a pre-Saalian age, thereby forming palaeovalley/basin fills in the post-Cretaceous topography. Till fabrics and glacial tectonics record expansions of local ice caps exclusively, suggesting wet-based ice cap advance, followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains and the Severnaya Zemlya archipelago, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with the exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice neither impacted the Chelyuskin Peninsula nor Severnaya Zemlya, and barely touched the northern coastal areas of the Taymyr Peninsula.     

Comments on Jansson, K.N. and Glasser, N.F. (2008) “Modification of peripheral mountain ranges by former ice sheets: The Brecon Beacons, southern UK,” Geomorphology 97, 178–189

Jansson and Glasser (Jansson, K.N., Glasser, N.F., 2008. Modification of peripheral mountain ranges by former ice sheets: the Brecon Beacons, southern UK. Geomorphology 97, 178–189.) have recently provided unconventional interpretations of selected glacial erosional and depositional landforms in the Brecon Beacons, UK, based on remotely sensed imagery. These new interpretations contradict well-established and reliable evidence for the origins and ages of certain glacial landforms of this upland area and elsewhere. They suggest that during a post-Last Glacial Maximum (LGM) ice-sheet event ice flowed up supposed, essentially “fluvial” valleys producing “glacial lineations” and depositing marginal moraines at the valley heads and on cirque floors. We argue that their interpretations of some key landforms are incorrect and that they have ignored much of the previous dating and field geomorphological evidence. Sedimentary and morphological evidence (e.g., lack of erratic content; convex planform with respect to the headwall; relatively large height range of moraines; and close association with headwall extent, height, and steepness) all indicate that higher level cirque-floor and valley-head moraines in the Brecon Beacons (> c. 400 m) were formed by cirque glaciers. Available dating evidence indicates a Younger Dryas age. We demonstrate that the supposed “fluvial” valleys, comprising trough heads with steep headwalls, have more nearly parabolic than V-shaped cross profiles indicating substantial glacial modification. Field evidence shows that proposed key exemplar post-LGM glacial lineations are in fact debris flow deposits. We conclude that whilst the adoption of a macroscale approach can shed new light on large-scale, ice-sheet movements, this approach should not be undertaken without consideration of the associated field evidence.