冰川,积雪及泥石流灾害研究的回顾与设想

文章总结了４０年来中国科学院兰州冻川冻土研究所在冰川,积雪和泥石流灾害研究中取得的重要成果与进展,分析了冰雪和泥石流灾害的形势,提出了灾害研究的主要方向,其中有加强全球变化对灾害形成和发展的影响研究,以及国家经济建设重心西移后,人类活动可能造成的各类灾害的预研究等,最后提出了应采取的一些措施。     

Supraglacial Debris Supply in the Cuerpo de Hombre paleoglacier (Spanish Central System): Reconstruction and Interpretation of a Rock Avalanche Event

During the deglaciation stages of the last glacial period a rock avalanche took place on the glacier that occupied the upper sector of the Cuerpo de Hombre Valley (Sierra de Béjar). The material displaced during the avalanche fell onto the ice, was transported by the glacier and later deposited as supraglacial ablation till. The cause of the avalanche was the decompression of the valley slopes after they were freed from the glacier ice (stress relaxation). Reconstruction of the ice masses has been carried out to quantify the stress relaxation that produced the collapse. The rock avalanche took place on a lithologically homogeneous slope with a dense fracture network. The avalanche left a 0.4 ha scar on the slope with a volume of displaced material of 623 ± 15 × 10³ m³. The deposit is an accumulation of large, angular, heterometric boulders (1–100 m³ in volume) with a coarse pebble‐size matrix. The avalanche can be explained as a relaxation process. This implies rock decompression once the glacier retreat left the wall ice free (debuttressing). Calculations show that the avalanche took place where the decompression stresses were highest (130–170 kPa). In the Spanish Central System paleoglaciers the largest accumulation of morainic deposits occurred after the glacial maximum and the earliest stages of the ice retreat. The process described here is used as an example to formulate a hypothesis that the largest accumulations of tills were formed in relation to enhanced slope dynamics once some glacier retreat had occurred.     

Recurrence of major flank landslides during the last 2-Ma-history of Reunion Island

New detailed swath bathymetry and backscatter data corroborate the existence of four large bulges on the submarine flanks of Reunion Island. These fan-shaped promontories are 20–25 km wide at the coastline and 70–150 km across the seafloor 40–50 km offshore. Their surfaces are characterized by a speckle sonar pattern, indicating the presence of large blocks up to several hundred meters across. Each bulge results from the superposition of multiple landslide deposits whose older ones are dissected and delimited by erosive channels as much as 200 m deep and 20 km long. The submarine flanks of Reunion Island are thus mostly built by accumulation of debris avalanche fans. Morphologic and geologic evidence define large subaerial source areas for these mass-wasting events. In particular, inferred headwalls of most landslides having affected the Piton des Neiges massif generally coincide with the boundaries of its cirques (Mafate, Salazie, and Cilaos), whereas recurrent landslides have resulted in the formation of large concentric amphitheatre structures through the Piton de la Fournaise massif. Thus, about 15 slide events accompanied growth of the Reunion Island shield since 2 Ma.Editorial responsibility: J. Stix     

The Acheron rock avalanche, Canterbury, New Zealand—morphology and dynamics

The 1100-year-old Acheron rock avalanche deposit lies in an active tectonic setting in Canterbury, New Zealand, and has a volume of ten million cubic metres and a runout distance 3.5 km. The deposit comprises intensely fragmented greywacke rock, and the processes of intense rock fragmentation during runout are postulated to have generated an isotropic dispersive stress. Dynamic simulation shows that the runout can be explained as a flow of dry granular material with a normal coefficient of friction, if the presence of an isotropic dispersive stress within the moving rock debris throughout the runout is assumed. The dispersive stress distribution required to model the rock avalanche runout and match velocities calculated from run-up traces is closely similar to that used to simulate the runout of the much larger Falling Mountain rock avalanche in a similar lithologic and tectonic setting. Both events thus behaved in a fundamentally similar fashion.     

碎屑流高风险区桩群防护结构优化布局研究

桩群是一种可有效耗散碎屑流运动能量,抑制碎屑流运动距离及速度的山地灾害防护结构。在碎屑流沟口与受灾体之间构建一组桩群减速带,可达到保护受灾体的目的。以物理模型试验为基础,开展弧型桩群、方型桩群和圆型桩群的沟槽型碎屑流冲击动力响应研究。讨论了3种不同类型的桩群对沟槽型碎屑流运动形态的影响,进一步开展弧型桩群的结构优化研究。结果表明：采用桩群结构可有效减小沟槽型碎屑流堆积距离并抑制其运动速度;3种不同形状桩群之间,弧型桩与方型桩的拦挡效果明显优于圆型桩;弧型桩由于凹槽式外型,对沟槽型碎屑流堆积面积、淤埋深度的抑制效果稍优于方型桩;在相同高度、直径等几何参数下,弧型桩体积比圆型桩小22.6%,比方型桩小39.2%,因此弧型桩的制作成本也相对较低;弧型桩排数从1排增加到3排,桩群拦挡率分别提升7.2%、4.5%;适量增加槽口与桩之间距离Ld可以有效提高弧型桩群防护结构的能量耗散效率。该研究可为桩群在沟槽型碎屑流防治工程中的应用提供理论及技术支持。     

Geomorphic Evidence of Ancient Catastrophic Flow Type Landslides in the Mid-mountain Ridges of the Western Flysch Carpathian Mountains

Ancient flow type landslides are relatively frequent fossil forms of the relief in mid-mountain conditions of the Czech Carpathian Mountains.Sixty rather distinctive displays of debris flows,rock avalanches,and debris avalanches have been mapped in the uppermost part of the territory.Unlike contemporary sporadic and low volume debris flows,ancient (Pleistocene and Lower Holocene) accumulations are a few orders of magnitude more extensive and were of considerable geomorphologic significance in forming the steep sections of mountain valleys and slopes.This geomorphic pattern does not hold for flow type slides,the source of which is material released as a consequence of numerous deep-seated landslides.Due to deep disruption of slopes,a few high-magnitude flow type landslides (e.g.,rock avalanches),quite rare in flysch mid-mountain conditions,also occurred in the Late Holocene.     

STARTER: a statistical GIS-based model for the prediction of snow avalanche susceptibility using terrain features—application to Alta Val Badia, Italian Dolomites

This article describes a methodology to localise areas with high potential towards natural snowpack instability under particular meteorological conditions, at the scale of an Alpine valley. Localisation is based on statistically relating known release areas of past avalanche events to maps of: (1) slope inclination, (2) slope orientation (aspect), (3) elevation, (4) distance from crest lines, (5) terrain roughness and (6) concavities/convexities. The maps have been built using two different GIS softwares while the statistical analyses have been performed with a specific software handling also Fuzzy Set theory algorithms. The results of the statistical analyses have been verified on test release—areas which have not been used as input data for the statistical analyses. Verification allowed to quantify how reliably the susceptibility values were calculated, to compare the values obtained using different combinations of terrain features and to finally decide on the most efficient combination. The susceptibility maps were calculated and verified for three different meteorological scenarios (given by three classes of snow depth). Verification has shown that the accuracy of the susceptibility maps was between 67% and 82%. The three susceptibility maps show a remarkable difference in the spatial pattern of the highest susceptibility pixels suggesting that for different meteorological scenarios different classes of terrain features need to be considered.The possibility to make combinations of terrain features and to assess and verify their statistical relationship with release areas of past avalanche events is the major original step made by STARTER. Linking those release areas to meteorological scenarios is an attempt to include in the analysis the combined influence of terrain features and meteorological conditions towards snowpack instability.     

An alternative depth-integrated formulation for granular avalanches over temporally varying topography with small curvature

An alternative formulation is proposed for deriving depth-integrated equations for gravity-driven granular avalanches over a non-trivial topography with small curvature. The coordinate system of Bouchut and Westdickenberg (2004 Bouchut, F and Westdickenberg, M. 2004. Gravity driven shallow water models for arbitrary topography. Commun. Math. Sci., 2: 359–389. [Crossref] , [Google Scholar]) is combined with the unified coordinate (UC) method, so that it can evolve in accordance with the entrainment–deposition processes at the basal surface. The resultant mass and momentum equations are formulated as a conservation system of the Cartesian components of the conservative physical variables. The motion of the flows is driven by the basal topography-induced pressure, pressure gradient, and resisted by the basal friction. The best benefit of this formulation is that it greatly simplifies the computation of the varying coordinate orientations. The features and advantages of this formulation are illustrated by the sliding-mass examples where we simulate the motion of a finite mass of granular material sliding down an inclined chute, running through a transition zone, and being deposited onto a horizontal plane.     

L'ı̂le de la Dominique, à l'origine des avalanches de débris les plus volumineuses de l'arc des Petites AntillesThe Island of Dominica,site for the generation of the most voluminous debris avalanches in the Lesser Antilles Arc

Results from recent fieldwork and the Aguadomar marine survey in the Lesser Antilles clearly indicate that the volcanic field of southern Dominica has experienced three major edifice collapse events. This led to formation of the most voluminous debris avalanches known in the Caribbean Arc. Submarine hummocky morphology with plurikilometric megablocks is characteristic of debris avalanche deposits. We propose that steep slopes on the western Caribbean side of the island and intense hydrothermal alteration lead to recurrent large-scale edifice collapses. Therefore islands in the Lesser Antilles face a non-negligible risk from generation of tsunamis associated with potential future edifice collapse. To cite this article: A. Le Friant et al., C. R. Geoscience 334 (2002) 235–243.