Assessment of geomorphic hazards in connection with permafrost occurrence in the Zugspitze area (Bavarian Alps, Germany)

In the Zugspitze area (Bavarian Alps, Germany), permafrost conditions are present in limestone bedrock and in regolith. Distribution is strongly dependent on topography in the east–west oriented mountain crest with steep north- and south-facing slopes. Numerous structures mainly for tourist purposes (cable car and recreation buildings, ski-lift masts, rack-railway tunnel, tunnel with supply facilities) are situated in the area, and several of them are placed on ground with permafrost. Results from a temperature measurement programme and distribution modelling show that for some of these constructions, the effects of permafrost degradation have to be considered in terms of stability of the foundations.The permafrost limit is close to the summit crest, and therefore, stability evaluations for the constructions in this area have to bear in mind the possible warming or even melting of ice within the bedrock crevasses caused by climate warming. Stability of the foundations as well as stability of rock walls in this area will probably be affected by a shifting of the permafrost limit. Constructions in the Zugspitzplatt area are already affected by the melting ground ice, and stabilizing measures have to be evaluated for several foundations where subsidence is likely to occur.Besides the local results, the study provides for the first time data on permafrost distribution in the northern Alpine margin based on standard methods of BTS measurements and numerical modelling.     

Lateglacial and Holocene talus slope development and rockwall retreat on Mynydd Du, UK

Modification of Lateglacial and Holocene talus sheets by debris flows and gully incision on Mynydd Du, Wales, has resulted in a convergence of upper slope form characterised by an upper rectilinear slope gradient of 36°±3° and a range of concavities of c. 0.1–0.2. In most cases, gully incision and accumulation of debris cones have led to an increase in slope concavity. Evidence for talus erosion, reworking and redeposition on the upper slope emphasises secondary reworking processes, as well as primary talus accumulation on the upper slope, and permits construction of a model of talus development at Mynydd Du. On the basis of talus volume, calculation of the first rockwall retreat data set for southern Britain suggests that c. 7.1 m (84%) of overall rockwall retreat (8.5 m) took place during the Lateglacial, and only c. 1.4 m (16%) occurred during the Holocene. These figures imply that Lateglacial retreat rates ranged from 1.01 to 2.44 m ka⁻¹, with an overall mean rate of 1.23 m ka⁻¹. In contrast, Holocene rockwall retreat rates range from 0.10 to 0.17 m ka⁻¹, with a mean rate of 0.12 m ka⁻¹. Approximately 27% of cliff retreat is attributed to microgelivation. While similar to Holocene and present-day alpine environments, these Lateglacial retreat rates are one order of magnitude higher than most equivalent values for arctic sites. This reflects both ‘alpine-style’ diurnal freeze–thaw activity on Mynydd Du during the Younger Dryas and paraglacial rock-mass instability following deglaciation. Assuming an exponential decline in rockwall sediment release, it is estimated that approximately half the talus had accumulated within c. 1 ka of deglaciation. At one site, paraglacial talus accumulation appears to have contributed significantly to the glacial sediment transport system of a subsequent ice advance. Present-day rates of rockwall retreat and talus accumulation by rockfall are estimated to be 0.014 and 0.022 mm yr⁻¹ (m ka⁻¹), respectively, similar to values for other British sites and markedly lower than Holocene rates of cliff recession due to microgelivation. By implication, the geomorphic significance of microgelivation may have been greatly underestimated in studies of inland rock-slope evolution in temperate, mid-latitude environments.     

Clast size variations on talus: Some observations from northwest Ireland

Clast size variations are reported for a relict talus slope in northwest Ireland. Alternating longitudinal zones of coarse debris below buttresses and less coarse debris below gullies give the talus pronounced lateral variations in clast size that are related to joint spacing variations in the talus source area. Longitudinal variations in clast size are also present. The talus accumulated predominantly by the process of rockfall. Other processes frequently associated with lateral size variations were not significantly effective during talus development. Talus sliding may have modified some patterns of rockfall size grading.     

Sāfitā castle and rockfalls in the ‘dead villages’ of coastal Syria – an archaeoseismological study

Sāfītā, a crusader fortification in Tartūs Governorate, coastal Syria, bears major damages of earthquake origin. The tower suffered heavy vibration, which produced fractures across the thick walls, widening the central portion of the building, and causing arch keystones to slide downwards. Apparently a ∼north–south strong motion was responsible for the damages. Further north, at Khirbat al-Qurshiyya, an abandoned village from Late Antiquity, a quarry abounds with fallen blocks. These display displacement predominantly in a northerly direction, suggesting a north–south strong motion. ‘Ayn-Qadīb, a small village in the Jabal Ansāriyya ranges, was damaged by a northward-directed rockfall. A contemporary letter testifies to the fact that Sāfītā donjon was heavily damaged by the AD 1202 earthquake. The Yammouneh Fault, which probably caused the damage, is only 50 km away further south.     

Stress state analysis of a collapsed overhanging rock slab: A case study

This paper describes the geomechanical back-analysis of the flexural failure of an overhanging limestone slab (volume = 68 m³) that collapsed on 26/01/1999 on the abandoned Cellina Valley state road SS 251 (western Friuli, NE Italy). The survey carried out on site examining the contact surfaces between the block and the slope has ascertained that the rock slab was connected to the stable rock mass by means of a single great rock bridge. The detailed reconstruction of the slab geometry and of the actual restraint conditions acting before the rockfall permitted an estimation of the stress state by using a 3D finite element code (Strand7). The finite element numerical model, referred to the restrained cross-section measured on site (A_res = 2.82 m²), gives a maximum value of σ_t = 5.19 MPa for the tensile stress, which is in good agreement with the estimated value for the characteristic strength mobilized at rupture by the intact rock material (T₀ = 3.5–5.5 MPa). Considerably lower maximum tensile stress (σ_t = 2.25 MPa), smaller than one half, is obtained if the whole contact surface is assumed as resisting surface (A_res = 10.50 m²) and the rock bridge is neglected.     

Evaluating seismically induced mass movement hazard in Caramanico Terme (Italy)

Mass movements and earthquakes represent two major geological hazards in the municipal territory of Caramanico Terme (south-central Apennines). Available records revealed the contemporaneous occurrence of earthquakes and slope failures on four occasions in the last four centuries (1627, 1706, 1933, and 1984). These events, with local intensities ranging from VI to IX, generated mass movements varying from a rotational slope failure to rock/block falls. All occurred in the southern periphery of the town and involved a thick carbonate megabreccia caprock and coarse colluvia which overlie a clayey substratum. Field investigation and review of historical records helped to delimit the areas susceptible to seismically triggered rockfalls. The mapping of historic and pre-historic rockfall deposits revealed their dispersal patterns and provided the basis for a determination of potential hazard zones. We approximate the temporal hazard assessment by relating the rockfall occurrence to the probability of earthquake triggering. Considering the VI degree triggering threshold indicated by local historical data, the statistical analysis of the regional seismic activity shows that events capable of inducing rockfalls have an approximately decennial recurrence in Caramanico. The approach presented could be readily applied to other potential risk areas of Italy by exploiting the rich long-term record of historical seismicity. In general, temporal hazard estimates at relatively low intensity levels will be possible even where the seismic history of the site is only well documented for a relatively limited time interval, provided that this interval is much longer than the recurrence time of the events exceeding the threshold considered.     

基于GIS技术的贵州省凯里市鱼洞崩塌灾害风险评估

崩塌地质灾害的致灾体具有隐蔽性特征,传统的调查手段难以查明所有的致灾体,而隐蔽性致灾体一旦失稳破坏,往往造成群死群伤的灾难事故.因此,如何提早识别与预防灾难的发生,成为地质灾害防治学者专家关注的焦点.以凯里市龙场镇崩塌灾害为例,运用GIS技术,采用风险评估的方法,对影响崩塌灾害发生的各因素进行叠加综合,从而分析出灾害的易发性、危险性和易损性,得到灾害的风险性,从而为灾害的预防提供参考与指导.     

Prototype of a wire-rope rockfall protective fence developed with three-dimensional numerical modeling

This study uses a numerical procedure, previously validated with data from full-scale experiments, to investigate the performance of a modified prototype wire-rope fence to provide protection against rockfall. The cost-reducing modifications are increased post spacing and fewer wire netting layers. The numerical procedure provides the nonlinear response of the prototype under various impact conditions and insights into each component’s role in dissipating impact energy. A simple but effective method to increase fence capacity is also developed. Finally, the use of two units of the prototype to protect a wide area is investigated employing the numerical procedure.     

Rockfalls into forests: Analysis and simulation of rockfall trajectories — considerations with respect to mountainous forests in Switzerland

Rockfalls are a major threat to settlements and transportation routes in many places. Although the general protective effect of forests against rockfalls is currently not questioned, little is known about the ideal properties of a forest stand that provides good protection. Therefore, in this study the question was assessed of how mountainous forests may influence rockfalls of single boulders. An actual rockfall trajectory was measured, recorded, analysed and simulated with a rockfall model. Rockfalls into different forest scenarios were also modelled for the site. Results showed that the actual rockfall event can be well simulated. Furthermore, a completely forested slope reduces velocity and energy of the falling blocks much better than a sparsely forested slope. For the profile discussed in this paper, the largest effect upon falling 3 m³ blocks was obtained with a high forest containing 350 trees per ha. The results confirmed common assumptions on ideal properties of a protective forest stand against rockfalls.     

Quantitative assessment of the residual risk in a rockfall protected area

Quantitative Risk Assessment (QRA) has become an indispensable tool for the management of landslide hazard and for planning risk mitigation measures. In this paper we present the evaluation of the rockfall risk at the Solà d’Andorra slope (Andorra Principality) before and after the implementation of risk mitigation works, in particular, the construction of protective fences. To calculate the risk level we have (i) identified the potential rockfall release areas, (ii) obtained the volume distribution of the falling rocks, (iii) determined the frequency of the rockfall events, and (iv) performed trajectographic analysis with a 3D numerical model (Eurobloc) that has provided both the expected travel distances and the kinetic energy of the blocks. The risk level at the developed area located at the foot of the rock cliff has been calculated taking into account the nature of the exposed elements and their vulnerability. In the Forat Negre basin, the most dangerous basin of the Solà d’Andorra, the construction of two lines of rockfall protection fences has reduced the annual probability of loss of life for the most exposed person inside the buildings, from 3.8×10⁻⁴ to 9.1×10⁻⁷ and the societal risk from 1.5×10⁻² of annual probability of loss of life to 1.2×10⁻⁵.