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1.
Geraint Owen John A. Matthews Richard A. Shakesby Xiubin He 《Geografiska Annaler: Series A, Physical Geography》2006,88(4):295-307
An unusual assemblage of landforms and deposits is described from upper Norangsdalen, Sunnmøre region, southern Norway, and interpreted as the product of snow‐avalanche events that vary in magnitude, frequency and debris content. An avalanche impact plunge pool, proximal scar and distal mound are associated with a coarse gravel deposit covering part of the valley floor. Landforms in this debris spread include gravel ridges, boulder lines, beaded ridges, fine sediment banked against and covering large boulders, and gravel clumps. Many of these landforms are aligned, indicating across‐valley transport radiating from the plunge pool. Features were mapped in the field and samples analysed for grain size and heavy‐mineral content. The debris spread is attributed to deposition by high‐energy, debris‐rich snow‐avalanche events that collect debris from large areas of the valley side, lower slopes and plunge pool. Aligned landforms develop through sediment transport in a basal shear zone, and randomly distributed gravel clumps represent melt pits following debris transport in the avalanche body. Air displacement ahead of larger avalanches is thought to have felled and tilted trees on the lower slopes of the distal valley side. Approximate ages of damaged trees allowed estimation of the frequency of snow‐avalanche events: (1) small, frequent events (several per annum) carry debris to the lower valley slopes and the plunge pool; (2) moderate events with an annual to decadal frequency maintain the pool–scar–mound complex; and (3) large, debris‐rich events with a decadal to centennial frequency add material to the debris spread. 相似文献
2.
GERAINT OWEN JOHN F. HIEMSTRA JOHN A. MATTHEWS LINDSEY J. MCEWEN 《Geografiska Annaler: Series A, Physical Geography》2010,92(4):421-436
A tongue‐like, boulder‐dominated deposit in Tverrbytnede, upper Visdalen, Jotunheimen, southern Norway, is interpreted as the product of a rock avalanche (landslide) due to its angular to subangular boulders, surface morphology with longitudinal ridges, down‐feature coarsening, and cross‐cutting relationship to ‘Little Ice Age’ moraines. The rock avalanche fell onto glacier ice, probably channelled along a furrow between two glaciers, and stopped on the glacier foreland, resulting in its elongated shape and long runout distance. Its distal margin may have become remobilized as a rock glacier, but a rock glacier origin for the entire landform is discounted due to lack of source debris, presence of matrix, lack of transverse ridges, and sparcity of melt‐out collapse pits. Lichenometric dating of the deposit indicates an approximate emplacement age of ad 1900. Analysis highlights the interaction of rock‐slope failures and glaciers during deglacierization in a neoparaglacial setting, with reduced slope stability due to debuttressing and permafrost degradation, and enhanced landslide mobility due to flow over a glacier and topographic channelling. Implications for the differentiation of relict landslides, moraines and rock glaciers are discussed and interrelationships between these landforms are considered in terms of an ice‐debris process continuum. 相似文献
3.
John F. Shroder Michael P. Bishop Luke Copland & Valerie F. Sloan 《Geografiska Annaler: Series A, Physical Geography》2000,82(1):17-31
The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris‐covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers. We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock‐glacier morphologies. 相似文献
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David J. Sauchyn 《自然地理学》2013,34(3):191-217
Much of the previous research on mountain debris slopes has focused on slopes of avalanche and, especially, rockfall origin. This study examines particle size and shape variation on some debris fans formed by rockfall, snow avalanches, and stream-debris flow on dissected rockwalls. The particle size and shape data are derived from the lengths of the 3 principal axes of 50 particles sampled at 152 stops on 24 transects. The analysis of these data indicates that variation in particle shape is a function of source rock lithology while particle size varies according to the process of coarse debris transfer. Most of the size variation occurs at the sampling stops and among stops within transects. Size means and variances differ according to process for samples not affected by stream-debris flow. Second-order polynomial regressions depict the longitudinal size sorting produced by each process and reflect the unique nature of debris transfer on dissected rockwalls, where rockfall is impeded and debris is sequentially or simultaneously subject to gravitational and boundary shear stresses. 相似文献
6.
西藏帕隆藏布河谷崩塌滑坡、泥石流的分布规律 总被引：11，自引：0，他引：11
西藏帕隆藏布河谷崩塌滑坡、泥石流灾害严重。崩塌滑坡、泥石流的分布 ,因谷坡坡向的水热条件差异而导致坡向差异 ,因地貌发育和形态的沿程分异显现沿程差异 ,因其促发条件的差异又显现灾种差异。采用有序样品最优分割和方差分析等定量方法 ,揭示了崩塌滑坡、泥石流的差异性分布规律 :全河段可分为上游峡谷泥石流密集段 ,中游宽谷泥石流及崩塌滑坡较密集段 ,和下游、拉月曲峡谷崩塌滑坡、泥石流极密集段 ;北岸崩塌滑坡和泥石流比南岸数量多、规模大 ;崩塌滑坡有向下游增大增多之趋势。进而对道路平面选线原则提出了建议。 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
8.
Probability of occurrence, hazard intensity and encounter probability are key parameters in the quantitative risk analysis (QRA) of landslides. All are strongly dependent on magnitude of the landslides. As a result, magnitude–frequency analysis should be a part of QRA. Deriving representative magnitude–frequency relationships for debris avalanches and debris flows, however, is difficult. One key problem is illustrated with the example of a unique database from the coastal region of British Columbia, Canada, which was compiled entirely from detailed ground investigations. The magnitude of debris avalanches and debris flows is not an independent statistical quantity, but a function of the scale of a given slope, as characterized by the slope length. Thus, attempting to derive probability and magnitude for a given location or sub-region from a regionally-derived magnitude–frequency curve may lead to incorrect predictions. The same problem is pertinent to the application of the same approach to any type of landslide in which the largest combined dimension of the source volume (including entrainment) is of the same order as the length of the slope. It is recommended that greater emphasis be placed on site-specific geological observations, at the expense of generalized statistics. 相似文献
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汶川地震对千佛山风景区造成严重的影响,直接诱发滑坡10处,崩塌数十处,形成大小堵塞坝4座,由此形成的松散物质总量大于1 700×104m3。2008年雨季有5条支沟暴发泥石流。在泥石流成因分析的基础上,选择流域形状、流域发育程度、沟床纵比降、山坡平均坡降、地层岩性和距发震断层距离6个指标,利用潜在泥石流判识模型,对流域内其余9条支沟进行了判断。结果显示,大部分沟道都具备形成泥石流的潜在条件。2009年雨季研究区全面暴发的大规模泥石流,验证判识的可靠性,表明该模型可以用于灾区潜在泥石流的判识。 相似文献
10.
Relief-rejuvenation and topographic length scales in a fluvial drainage basin, Napf area, Central Switzerland 总被引：2，自引：2，他引：2
This paper explores how, and to what extent, a phase of relief-rejuvenation modifies the mode of surface erosion in an approximately 63 km2 drainage basin located at the northern border of the Swiss Alps (Luzern area). In the study area, the retreat of the Alpine glaciers at the end of the Last Glacial Maximum (LGM) caused base level to lower by approximately 80 m. The fluvial system adapted to the lowered base level by headward erosion. This is indicated by knickzones in the longitudinal stream profiles and by the continuous upstream narrowing of the width of the valley floor towards these knickzones. In the headwaters above these knickzones, processes are still to a significant extent controlled by the higher base level of the LGM. There, frequent exposure of bedrock in channels and especially on hillslopes implies that sediment flux is to a large extent limited by weathering rates. In the knickzones, however, exposure of bedrock in channels implies that sediment flux is supply-limited, and that erosion rates are controlled by stream power.The morphometric analysis reveals the existence of length scales in the topography that result from distinct geomorphic processes. Along the tributaries where the upstream sizes of the drainage basins exceed 100,000–200,000 m2, the mode of sediment transport and erosion changes from predominantly hillslope processes (i.e., landsliding, creep of regolith, rock avalanches and to some extent debris flows) to processes in channels (fluvial processes and debris flows). This length scale reflects the minimum size of the contributing area for channelized processes to take over in the geomorphic development (i.e., threshold size of drainage basin). This threshold size depends on the ratio between production rates of sediment on hillslopes, and export rates of sediment by processes in channels. Consequently, in the headwaters, erosion rates and sediment flux, and hence landscape evolution rates, are to a large extent limited by weathering processes. In contrast, in the lower portion of the drainage basin that adjusts to the lowered base-level, rates of channelized erosion and relief formation are controlled mainly by stream power. Hence, this paper shows that base-level lowering, headward erosion and establishment of knickzones separate drainage basins in two segments with different controls on rates of surface erosion, sediment flux and relief formation. 相似文献
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12.
Goro Komatsu Sergei G. Arzhannikov Anastasia V. Arzhannikova Kirill Ershov 《Geomorphology》2007,88(3-4):312-328
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. 相似文献
13.
Initiation conditions for debris flows generated by runoff at Chalk Cliffs, central Colorado 总被引：7，自引：1，他引：6
We have monitored initiation conditions for six debris flows between May 2004 and July 2006 in a 0.3 km2 drainage basin at Chalk Cliffs; a band of hydrothermally-altered quartz monzonite in central Colorado. Debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14° to 45°. The availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes. Rainfall exceeding I = 6.61(D)− 0.77, where I is rainfall intensity (mm/h), and D is duration (h), was required for the initiation of debris flows in the drainage basin. The approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0.15 m3/s. Colluvium in the basin was unsaturated immediately prior to (antecedent) and during debris flows. Antecedent, volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4–9%, and 4–7%, respectively. During debris flows, peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10–20%, and 4–12%, respectively. Channel sediment at a depth of 45 cm was unsaturated before and during debris flows; antecedent moisture ranged from 20–22%, and peak moisture ranged from 24–38%. Although we have no measurements from shallow rill or channel sediment, we infer that it was unsaturated before debris flows, and saturated by surface-water runoff during debris flows.Our results allow us to make the following general statements with regard to debris flows generated by runoff in semi-arid to arid mountainous regions: 1) high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff, 2) locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows, and 3) rainfall and simulated surface-water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment. 相似文献
14.
Understanding the scale and frequency of physical processes that act upon and form the surface of the Earth is a fundamental goal of earth science. Here we determine the magnitudes of landslides that impact the landscape in terms of work, persistence, and formative events. A systematic analysis of rapid landsliding (the analysis did not consider creep and other slow semi-continuous processes) indicates that moderate-sized landslides do the most work transporting material on hillslopes. The work peak defines the moderate magnitude, and that magnitude varies based on local physiography and climate. Landslides that form the work peak are distinct from catastrophic landslides that are themselves formative and system resetting. The persistence time for debris slides/debris flows (PDS) and rock slides/rock avalanches (PRS) is calculated over six orders of magnitude. We consider an event catastrophic when it persists in the landscape, as described by a persistence ratio (PF), an order of magnitude longer than the population of landslides that form the work peak. 相似文献
15.
Formation and failure of volcanic debris dams in the Chakachatna River valley associated with eruptions of the Spurr volcanic complex, Alaska 总被引：1，自引：0，他引：1
Christopher F. Waythomas 《Geomorphology》2001,39(3-4)
The formation of lahars and a debris avalanche during Holocene eruptions of the Spurr volcanic complex in south-central Alaska have led to the development of volcanic debris dams in the Chakachatna River valley. Debris dams composed of lahar and debris-avalanche deposits formed at least five times in the last 8000–10,000 years and most recently during eruptions of Crater Peak vent in 1953 and 1992. Water impounded by a large debris avalanche of early Holocene (?) age may have destabilized an upstream glacier-dammed lake causing a catastrophic flood on the Chakachatna River. A large alluvial fan just downstream of the debris-avalanche deposit is strewn with boulders and blocks and is probably the deposit generated by this flood. Application of a physically based dam-break model yields estimates of peak discharge (Qp) attained during failure of the debris-avalanche dam in the range 104<Qp<106 m3 s−1 for plausible breach erosion rates of 10–100 m h−1. Smaller, short-lived, lahar dams that formed during historical eruptions in 1953, and 1992, impounded smaller lakes in the upper Chakachatna River valley and peak flows attained during failure of these volcanic debris dams were in the range 103<Qp<104 m3 s−1 for plausible breach erosion rates.Volcanic debris dams have formed at other volcanoes in the Cook Inlet region, Aleutian arc, and Wrangell Mountains but apparently did not fail rapidly or result in large or catastrophic outflows. Steep valley topography and frequent eruptions at volcanoes in this region make for significant hazards associated with the formation and failure of volcanic debris dams. 相似文献
16.
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
17.
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. 相似文献
18.
G. WADGE 《International journal of geographical information science》2013,27(2):143-152
Abstract The component of gravitational acceleration parallel to the slope of the local surface partly determines the state of slope stability and the kinematics of flow under gravity on that slope. Geographical information systems based on digital elevation models offer the potential to be able to map this variable and permit the modelling of a variety of stability criteria and surface processes including landslides, rock avalanches, pyroclastic flows and lava flows. Three types of models and the basic map operations required to run them are discussed. The models are as follows: (i) sites of potential shallow slope failure (e.g. landslides), (ii) maps of flow deposition based on energy balance calculations (e.g. rock avalanches) and (iii) finite difference, initial value type simulations of dynamic flow (e.g. lava flows). The potential value of these models to hazard assessment is great but their application in specific cases must be assessed with reference to the accuracy of the digital elevation model used. 相似文献
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Surface sediment characteristics and present dynamics in alluvial fans of the central Spanish Pyrenees 总被引：3，自引：0，他引：3
Three alluvial fans in the Ribera de Biescas, upper Gállego Valley, and central Spanish Pyrenees, have been studied in order to explain the most recent changes and to identify the spatial organization of the sediment. In the alluvial fans surveyed, the proximal area is dominated by debris flows, which pass downslope into transitional and fluvial deposits. The relative importance of each type of sediment is closely related to the size and gradient of the alluvial fan, as well as to the gradient in the final stretch of the stream. In general, the size of the sediment decreases from the proximal to the distal area, while the roundness increases. Nevertheless, there are noticeable irregularities in the trend both in longitudinal and transverse transects, due mainly to the sedimentary dynamics of the debris flows, as they advance towards the inner part of each alluvial fan during the most intense peak flows. A sudden shrinkage of the most active area and incision along the fan channels has been assessed and related to land-use changes in the catchments. 相似文献