Scree Research Articles

Field observations of debris-flow initiation processes on sediment deposits in a previous deep-seated landslide site

Although information regarding the initiation processes of debris flows is important for the development of mitigationmeasures, field data regarding these processes are scarce. We conducted field observations of debris-flow initiation processes in the upper Ichinosawa catchment of the Ohya landslide, central Japan. On 19 June 2012, our video-camera monitoring systems recorded the moment of debris-flow initiation on channel deposits (nine surges) and talus slopes (eight surges). The initiation mechanisms of these surges were classified into three types by analyzing the video images: erosion by the surface flow, movement of deposits as a mass, and upward development of the fluid area. The first type was associated with the progress of surface flow from the upper stream on unsaturated channel deposits. The second type was likely caused by an increase in the pore water pressure associated with the rising in the groundwater level in channel deposits; a continuous water supply from the upper stream by the surface flow might have induced this saturation. The third type was associated with changes in the downstream topography caused by erosion. The flow velocity of most surges was less than 3 m s-1 and they usually stopped within 100 m from the initiation point. Surges with abundant pore fluid had a higher flow velocity (about 3 - 5 m s-1) and could travel for a longer duration. Our observations indicate that the surface flow plays an important role in the initiation of debris flows on channel deposits and talus slopes.

Regional-scale controls on the spatial activity of rockfalls (Turtmann Valley, Swiss Alps) — A multivariate modeling approach

In mountain geosystems, rockfalls are among the most effective sediment transfer processes, reflected in the regional-scale distribution of talus slopes. However, the understanding of the key controlling factors seems to decrease with increasing spatial scale, due to emergent and complex system behavior and not least to recent methodological shortcomings in rockfall modeling research. In this study, we aim (i) to develop a new approach to identify major regional-scale rockfall controls and (ii) to quantify the relative importance of these controls. Using a talus slope inventory in the Turtmann Valley (Swiss Alps), we applied for the first time the decision-tree based random forest algorithm (RF) in combination with a principal component logistic regression (PCLR) to evaluate the spatial distribution of rockfall activity. This study presents new insights into the discussion on whether periglacial rockfall events are controlled more by topo-climatic, cryospheric, paraglacial or/and rock mechanical properties.(i)Both models explain the spatial rockfall pattern very well, given the high areas under the Receiver Operating Characteristic (ROC) curves of >0.83. Highest accuracy was obtained by the RF, correctly predicting 88% of the rockfall source areas. The RF appears to have a great potential in geomorphic research involving multicollinear data.(ii)The regional permafrost distribution, coupled to the bedrock curvature and valley topography, was detected to be the primary rockfall control. Rockfall source areas cluster within a low-radiation elevation belt (2900–3300ma.s.l,) consistent with a permafrost probability of >90%. The second most important factor is the time since deglaciation, reflected by the high abundance of rockfalls along recently deglaciated (<100years), north-facing slopes. However, our findings also indicate a strong rock mechanical control on the paraglacial rockfall activity, declining either exponentially or linearly since deglaciation.The study demonstrates the benefit of combined statistical approaches for predicting rockfall activity in deglaciated, permafrost-affected mountain valleys and highlights the complex interplay between rock mechanical, paraglacial and topo-climatic controls at the regional scale.

Low genetic diversity, restricted dispersal, and elevation-specific patterns of population decline in American pikas in an atypical environment

AbstractIn the face of climate change, there is a growing need for research into the ability of organisms to persist at the limits of their bioclimatic envelope. American pikas ( Ochotona princeps ) have emerged as a focal mammalian species for investigating extinction risk related to climate change; however, most studies have occurred in characteristic alpine talus habitat within the range core. In the Columbia River Gorge (CRG), Oregon, American pikas inhabit low-elevation talus slopes previously considered outside the species’ bioclimatic range. We used microsatellite genotypic data to reconstruct levels of genetic variation, population connectivity, and demographic history at 11 CRG sites spanning an elevational gradient (104–1,292 m). Sampled sites separated into 2 genetic clusters largely explained by elevation, topography, and geographic proximity, with pairwise estimates of differentiation and migration rates suggesting little gene flow may be occurring. Sites were characterized by levels of allelic richness and heterozygosity substantially lower than values reported at characteristic alpine sites from the range core. Evidence of recent demographic contraction was found almost exclusively at high-elevation sites despite these areas being considered refuges from climate warming in more typical habitat. Given their unique genetic characteristics and persistence in an atypical environment, the CRG pika populations likely constitute a significant component of intraspecific biodiversity with high conservation value.

Post-Little Ice Age Development of a High Arctic Paraglacial Beach Complex

We reconstruct the behaviour of a High Arctic gravel-dominated beach complex that has developed in central Spitsbergen, Svalbard, since the end of the Little Ice Age (LIA). The studied coastal environment in northern Billefjorden (Petuniabukta) is characterised by limited wave action and ephemeral sediment delivery from non-glaciated, mainly snow-fed fans and talus slopes. Aerial photographic evidence and morpho-sedimentological observations of a beach-ridge plain and spit complex in northern Billefjorden reveal a dynamic coastal system. During the post-LIA period, a prominent coastal barrier at the mouth of the Ebbaelva migrated seawards several tens of metres and prograded northwards to form new spit systems, each > 150 m in length. The post-LIA coastal evolution occurred in two main phases. In the first half of the 20th century, increased paraglacial sediment released by retreating land-based glaciers led to the development of a subaqueous spit platform and the progradation of an ebb-tide delta into the mouth of the Ebbaelva, diverting its mouth to the northwest. In the second half of the 20th century, the barrier prograded onto this platform, promoting the development of three massive spits. Sedimentological data suggest that changes in beach-ridge composition that occurred during the 20th century are linked to episodic sediment delivery from an adjacent permafrost and snow-fed alluvial fan and delta system. Our work provides a basis for a new model of paraglacial barrier development that recognises the fundamental role of climate and sediment supply as two intimately connected processes that control coastal development in the High Arctic over decadal to centennial timescales. Copyright © 2015 John Wiley & Sons, Ltd.

Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

On 12 November 2014, the European mission Rosetta delivered the Philae lander on the nucleus of comet 67P/Churyumov-Gerasimenko (67P). After the first touchdown, the lander bounced three times before finally landing at a site named Abydos. Aims. We provide a morphologically detailed analysis of the Abydos landing site to support Philae’s measurements and to give context for the interpretation of the images coming from the Comet Infrared and Visible Analyser (CIVA) camera system onboard the lander. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 6 December 2014 to perform the analysis of the Abydos landing site, which provided the geomorphological map, the gravitational slope map, the size-frequency distribution of the boulders. We also computed the albedo and spectral reddening maps. Results. The morphological analysis of the region could suggest that Philae is located on a primordial terrain. The Abydos site is surrounded by two layered and fractured outcrops and presents a 0.02 km2 talus deposit rich in boulders. The boulder size frequency distribution gives a cumulative power-law index of −4.0 + 0.3/ − 0.4, which is correlated with gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. The average value of the albedo is 5.8% at λ1= 480.7 nm and 7.4% at λ2= 649.2 nm, which is similar to the global albedos derived by OSIRIS and CIVA, respectively.

Can tree tilting indicate mechanisms of slope movement?

Slope movements are a common natural hazard. That is why considerable funds are spent annually to limit their effects or to research their prevention. This study evaluates dendrometric approaches as a fast and low-cost alternative to classical methods of slope movement mechanism analysis. A total of 1688 trees growing on the Mazák landslide in the Moravskoslezské Beskydy Mts. and 100 reference trees growing out of the landslide area were analysed. The Mazák landslide is approximately 400m in length and presents varied morphological features (scarps, rotated blocks, scree slopes, shallow landslide areas, etc.). The slope and direction of stem inclination was recorded for each tree. The results were categorized into four distinct landforms (scarp with outcrops of bedrock, scree slope, front of partial landslide block, plateau of partial landslide block) and were then compared with parameters for the reference trees.The general model of tree tilting for the landslide area was verified and partially confirmed. Trees growing on the plateau of rotated blocks are predominantly oriented upslope; trees growing on scree slopes of shallow movement and creep are predominantly oriented downslope. Trees growing on rocky scars do not differ significantly from the reference trees. Trees growing from fronts of rotated blocks are oriented both upslope and downslope. From these results, several recommendations regarding dendrometric evidence of slope movement mechanisms are presented: (i) all trees growing on the landslide are to be analysed; (ii) old trees maintain stem tilt intensities and directions for long periods, but young trees are more sensitive to ground movements; (iii) tree root depth influences root sensitivity to movements of various depths; (iv) the general shape of a stem can denote specific mechanisms of slope movement and (v) comparisons with reference trees should always be conducted to exclude potential non-geomorphic effects on tree stem tilt.

Depositional facies and sequence of the latest Pleistocene to Holocene incised valley fill in Kushiro Plain, Hokkaido, northern Japan

The development of the latest Pleistocene to Holocene incised valley fill in the Kushiro area, Hokkaido, Japan is investigated in this study. Nine boring core samples drilled in the Kushiro marsh were examined using depositional facies analysis, total sulfur content (TSC) measurement, and radiocarbon dating methods. Based on these methods, 12 depositional facies were recognized including marsh, subaqueous talus, bay-head delta, sand dune, beach, shoreface, barrier sand body, drowned valley-central basin, salt marsh, fluvial, pond, and pyroclastic deposits. The incised valley fill forms a depositional sequence primarily controlled by glacio-eustatic sea-level changes. The lowstand systems tract is composed of river deposits. The transgressive systems tract includes salt marsh, drowned-valley fill central basin, bay-head delta, barrier sand body, central basin, and subaqueous talus deposits. The highstand systems tract is composed of barrier sand body, shoreface, beach, sand dune, central basin bay-head delta, marsh, salt marsh, subaqueous talus, fluvial, and pond facies. Radiocarbon dating analysis indicates that the period of maximum marine flooding was around 7 ka cal. BP.

Morphology of forest ravined soil formation on deluvial loams

The paper establishes the general features of the soil morphogenesis in ravined forests of Dnieper Prysamaria and genetic relationships of forest soils with zonal chernozem under herbaceous associations based on the detection of morphological properties that are «lithogenic», that is inherited from deluvial material and «pedogenic» features formed directly in the forest soil. The study area is located on the Dnieper Prysamaria (Dnipropetrovsk region) within the area of the steppes. The trial areas are incorporated in the upper Deep ravine, located in the upland part of watershed landscape. Catena is represented by five typical sections – between edging of the ravined forest and the field in the middle thirds of the slopes of the northern and southern exposures and in the thalweg of the ravine. Samples for meso-morphological studies were selected by genetic horizons, samples for soil horizons were selected using a soil drill. Basic morphological characteristics were determined in the laboratory (except for the hardness index). The mathematical processing of the results was carried out by methods of nonparametric statistics (method K-means). It was found that, despite the temporal and spatial disorder of deluvial material deposition processes and the differences of the water regime in the thalweg on the slopes, in the ravined biogeocenoses the forest soils are formed with common features of morphological organization of the genetic profile of the individual and morphological properties. The uniformity of the general structure is shown in a set sequence and the power of the genetic horizons, polycyclic and texture eluvial-illuvial differentiation of the genetic profile. The uniformity of the changes in the profile of the individual morphological properties is shown in the form of colour options of genetic horizons (due to humus content talus deposits), changing the particle size distribution of horizons in accordance with the general differentiation profile on eluvial and illuvial (due lessivage) part, changes in the morphology and dimensions of structural units related to changes in the structure of hardness horizons intensive leaching of carbonates from the profile of forest soils. The necessity of research processes clayization profile in situ, their role in the morphogenesis of compacted horizons are noted. There are two groups of properties that make it possible to analyze the micromorphology level communication between the soils in the catena. The first – a lithogenic conditionally or diluvial material properties, which persist for a long time in a forest soil – granulometry and less coloration horizons. The second – a pathogenic properties, sharply differing in the studied soils associated with the peculiarities of morphogenesis of a particular genetic profile and specific genetic horizon. These include the level of occurrence of carbonates in the profile and intensity of effervescence, the morphology of the structural units, the hardness of the genetic horizons, the level of spot colour. Cluster analysis identified a statistically illustrates the differences between the morphological structure of the soil catena, combining in one cluster the ravined soils on deluvial deposits under forest vegetation, and in the other – the soils on the loess under herbaceous vegetation. The contrast of differences increases down the profile.

Pierre3D: a 3D stochastic rockfall simulator based on random ground roughness and hyperbolic restitution factors

The use of dynamic computational methods has become indispensable for addressing problems related to rockfall hazard. Although a number of models with various degrees of complexity are available, model parameters are rarely calibrated against observations from rockfall experiments. A major difficulty lies in reproducing the apparent randomness of the impact process related to both ground and block irregularities. Calibration of rigorous methods capable of explicitly modeling trajectories and impact physics of irregular blocks is difficult, as parameter spaces become too vast and the quality of model input and observation data are insufficient. The model presented here returns to the simple “lumped-mass” approach and simulates the characteristic randomness of rockfall impact as a stochastic process. Despite similarities to existing approaches, the model presented here incorporates several novel concepts: (i) ground roughness and particle roughness are represented as a random change of slope angle at impact; (ii) lateral deviations of rebound direction from the trajectory plane at impact are similarly accounted for by perturbing the ground orientation laterally, thus inducing scatter of run-out directions; and (iii) a hyperbolic relationship connects restitution factors to impact deformation energy. With these features, the model is capable of realistically accounting for the influence of particle mass on dynamic behaviour. The model only requires four input parameters, rendering it flexible for calibration against observed datasets. In this study, we calibrate the model against observations from the rockfall test site at Vaujany in France. The model is able to reproduce observed distributions of velocity, jump heights, and runout at observation points. In addition, the spatial distribution of the trajectories and landing points has been successfully simulated. Different parameter sets have been used for different ground materials such as an avalanche channel, a forest road, and a talus cone. Further calibration of the new model against a range of field datasets is essential. This study is part of an extensive calibration program that is still in progress at this first presentation of the method, and focuses on fine-tuning the details of the stochastic process implemented both in two-dimensional (2D) and three-dimensional (3D) versions of the model.

Exceptional invertebrate diversity in a scree slope in Eastern Spain

In this study, the invertebrate fauna of a colluvial Mesovoid Shallow Substratum (MSS) is Eastern Spain was characterized, and the importance of the MSS as refuge for endemic and rare species was assessed. Ten pitfall traps were buried up to 1 m deep inside multiperforated PVC tubes across a stone debris. Several environmental variables were measured in each sampling point. The completeness of the inventory was assessed, and different diversity patterns—variation in abundance, species richness and species composition—were analyzed. 4150 individuals and 164 species were captured, most of them arthropods. The number of individuals and species varied considerably among traps. Half of the species were represented by one or two individuals, and neither the species accumulation curves nor the curves for the non-parametric estimators showed any sign of stabilizing. Individuals of abundant species aggregated in one or a few traps. No consistent diversity patterns were found, except that distance among traps partially explained the similarity in species composition when considering only the most abundant species. This is a very rich but uneven assemblage that shows a high degree of species turnover between traps. One-sixth of the species can be classified as either troglobionts or troglophiles, but there is a significant presence of edaphic species. Obtaining complete fauna inventories in the MSS has proven to be a challenging task. The study of the MSS reveals important faunistic information, providing new taxa to science as well as interesting records of poorly known species.

Flora and vegetation of Cape Hallett and vicinity, northern Victoria Land, Antarctica

Cape Hallett (72°19′S; 170°13′E) lies at the northern end of the western coastline of the Ross Sea region, and, to date, there appears to be no full description of its terrestrial flora despite its probable importance in understanding links between biodiversity and latitude. Here we present information about lichens and mosses from published papers, herbarium collections and personal surveys for Cape Hallett and seven nearby sites. A total of 59 lichen and 11 moss species are reported for these eight sites. Cape Hallett is one of the richest sites for terrestrial biodiversity in the Ross Sea region with about 46 lichen species and nine species of bryophytes. Lichens have their greatest diversity on the upper scree and summit area (30 species, 330 m), the least within the large penguin colony at sea level (one species). The station at Cape Hallett was established in 1957, and some of the earliest ecological and ecophysiological studies in Antarctica were carried out there. Historical comparisons are possible and have revealed considerable changes in vegetation in the lower flush area, a high level of frost heave disturbance, new lichen growth rate estimates for northern Victoria Land and extreme stability of the snow banks on the scree slopes. Cape Hallett represents a very important site for studies on links between terrestrial flora and the environment as well as on possible effects of climate change.

Effect of landscape fires on the demography of the endangered New Caledonian conifer Callitris sulcata

New Caledonia is a global biodiversity hotspot and an epicentre for Gondwanan conifers, many of which are threatened by mining and by altered fire regimes. We studied the distribution, abundance and demography of the endangered Callitris sulcata. The largest populations are restricted to one river system in the south-east of the island, with satellite populations in adjoining rivers. The local distribution is controlled by the fire protection afforded by terrain features such as scree slopes, creeklines and small cliffs. Adult trees, which have comparatively thick bark, are able to tolerate and recover from infrequent surface fires, but severe fires kill trees and the seeds they store, a pattern similar to that in many Australian Callitris species. Radiocarbon dating revealed the species is slower growing than Australian Callitris species, possibly due to the extreme infertility of the ultramafic soils. The species is of high cultural value to the indigenous population who also prizes the durable and aromatic timber, and harvests have been traditionally regulated. Illegal cutting of trees has become a problem, but uncontrolled fires, which have caused substantial population declines, dwarf this threat. Given these threats, conservation of the species hinges on ensuring some populations remain remote and rarely visited by humans.

Hypsometric analysis of headwater rock basins in the dolomites (eastern alps) using high‐resolution topography

Hypsometric curves and integrals are effective tools for rapid quantitative assessments of topography. High‐resolution digital terrain models derived from airborne data have been analysed to study the hypsometry of small headwater rock basins (drainage areas up to 0.13 km2) in three study areas in the Dolomites (astern lps) that have similar lithologies and climatic conditions. Hypsometric curves in the studied rocky headwaters display a variety of shapes and present remarkable differences between neighbouring basins. Hypsometric integrals show generally high values in the three study areas (>0.42, mean values between 0.51 and 0.65). The extent of the scree slopes located at the foot of rock basins in the three study areas is larger in the area with lower hypsometric integrals and indicates consistency between the development of basin erosion, which is shown by the hypsometric integral, and debris yield, represented by the extent of scree slope. No clear relations were observed between the hypsometric integrals and basin area and shape. When extending the analysis to larger basins, which encompass rocky headwaters and downslope soil‐mantled slopes, a negative correlation is found between the hypsometric integral and catchment area, suggesting that the scale independency of the hypsometric integral occurs essentially in headwater rock basins. Geomorphometric indices (residual relief and surface roughness) have contributed to interpreting the variability of surface morphology, which is related to the geo‐structural complexity of the catchments.

Stealth export of hydrogen and methane from a low temperature serpentinization system

Chemical input to the deep sea from hydrothermal systems is a globally distributed phenomenon. Hydrothermal discharge is one of the primary mechanisms by which the Earth’s interior processes manifest themselves at the Earth’s surface, and it provides a source of energy for autotrophic processes by microbes that are too deep to capitalize on sunlight. Much is known about the water-column signature of this discharge from high-temperature mid-ocean Ridge (MOR) environments and their neighboring low-temperature counterparts. Hydrothermal discharge farther away from the ridge, however, has garnered less attention, owing in part to the difficulty in finding this style of venting, which eludes methods of detection that work well for high-temperature ‘black smoker’-type venting. Here we present a case study of the plume from one such ‘invisible’ off-axis environment, The Lost City, with an emphasis on the dissolved volatile content of the hydrothermal plume. Serpentinization and abiotic organic synthesis generate significant concentrations of H2 and CH4 in vent fluid, but these species are unevenly transported to the overlying plume, which itself appears to be a composite of two different sources. A concentrated vent cluster on the talus slope channels fluid through at least eight chimneys, producing a water-column plume with the highest observed concentrations of CH4 in the field. In contrast, a saddle in the topography leading up to a carbonate cap hosts broadly distributed, nearly invisible venting apparent only in its water-column signals of redox potential and dissolved gas content, including the highest observed plume H2. After normalizing H2 and CH4 to the 3He background-corrected anomaly (3HeΔ) to account for mixing and relative amount of mantle input, it appears that, while a minimum of 60% of CH4 is transported out of the system, greater than 90% of the H2 is consumed in the subsurface prior to venting. The exception to this pattern occurs in the plume originating from the area dubbed Chaff Beach, in which somewhat more than 10% of the original H2 remains, indicating that this otherwise unremarkable plume, and others like it, may represent a significant source of H2 to the deep sea.

Soil geomorphology and frozen ground conditions at a subalpine talus slope having permafrost in the eastern Swiss Alps

At a subalpine site with permafrost below the timberline in the eastern Swiss Alps the complex interrelationship between different environmental factors was investigated by applying an integrated approach that combines soil mapping, 3D near-surface geophysics and surface and subsurface temperature monitoring. The objectives of this approach were to explore the 3D extension of isolated permafrost bodies and to relate this to surface parameters such as soils and humus forms and other extrinsic factors. Using this procedure, interdependencies between surface (soil properties and humus forms) and subsurface factors (ground thermal regime and frozen ground conditions) could be independently analysed. Although time-consuming, 3D ERI (electrical resistivity imaging) demonstrated its ability for precise permafrost mapping. Despite climate warming, super-cooling in winter along the investigated scree slopes is still efficient enough for establishing permafrost conditions. By comparing the spatial dimensions of the permafrost bodies with surface conditions, we found that thick moss or organic litter layers had an insulating effect and prevented the permafrost from melting. However, the comparison of soil units and soil thickness with the permafrost distribution did not always show an obvious relationship. This indicates that there is a complex evolution and behaviour of soils and permafrost at such sites.

Near-Surface Geophysical Imaging of a Talus Deposit in Yosemite Valley, California

Talus at the base of cliffs in Yosemite Valley, CA, represents rock fall and debris avalanche accumulation occurring since the glacial retreat after the last glacial maximum. This ongoing mass wasting subjects humans and infrastructure to hazards and risk. In order to quantify post-glacial rock-fall rates, talus volumes are needed for the deposits of interest. We used three near-surface geophysical methods (ground penetrating radar, electrical resistivity, and seismic refraction) to locate the basal contact of talus below Glacier Point, near Curry Village in the eastern Yosemite Valley. The coarseness of the talus deposit limited our ability to use these methods in some areas, and the geometry at the base of the cliff restricted our ability to conduct seismic refraction and electrical resistivity across the talus-bedrock boundary there. Nonetheless, we were able to detect the basal boundary of talus on top of both bedrock and glacio-fluvial sediment fill. Geophysical imaging revealed an apparent onlapping relationship of talus over aggrading post-glacial sediment fill, and our data support the proposition of approximately 5 m of valley floor aggradation since deglaciation. The bedrock-talus contact is characterized by a dip of 52–64°, consistent with the dip of the cliff surface above the talus apex. Ground penetrating radar and resistivity were the most diagnostic methods, in addition to being the most rapid and easiest to implement on this type of deposit.

Complex hydraulic interactions between compartmentalized carbonate aquifers and heterogeneous siliciclastic successions: a case study in southern Italy

The sedimentary sequences containing lithologic units with low permeability represent hydrogeologic systems, which, as of now, have been little studied despite their diffusion worldwide. A hydrogeologic study, aimed to assess the main factors controlling the groundwater flow dynamics in such systems and their hydraulic interactions with nearby carbonate aquifers, has been carried out in Longano (Isernia, Southern Italy). The analysis of the hydraulic heads, combined with the regimes of the springs and the electric conductivity of the groundwater, mainly reflect vertical and lateral heterogeneities of the media in terms of hydraulic properties. In particular, the flow system is controlled by lateral heterogeneities, which characterize a surficial horizon made up of clayey colluviums and talus deposits, separated from the deeper saturated, fissured bedrock. One-to-ten relationships in hydraulic heads, monitored in piezometers crossing the fissured media, further uphold the crucial role played by the lateral contrasts of permeability in controlling the flow dynamics. On the whole, significant interactions with the nearby carbonate hydrostructure take place. Nevertheless, the heterogeneities of the siliciclastic succession and surficial horizon, coupled with the compartmentalization of the carbonate system, lead to a complex hydrogeological scenario. In a wider perspective, this study gives information of utmost importance in order to improve the implementation of mathematical models and configuration of tapping works within these heterogeneous and complex settings. Copyright © 2015 John Wiley & Sons, Ltd.

Investigation on protalus ramparts in the Swiss Alps

Abstract. The origin and classification of landforms denominated as "protalus ramparts" in the scientific literature is a problem that is far from being resolved. The main objective of this contribution is to support a permafrost-related definition of protalus ramparts. If we consider the Alpine framework, protalus ramparts are generally very rare landforms; by contrast, the Alpine periglacial belt is characterised by a large diffusion of talus slopes and talus rock glaciers. The investigations carried out in six sites of the Valais Alps (Switzerland) allow eight major "diagnostic criteria" to be presented that help to define protalus ramparts in Alpine environments and that support the permafrost-related genesis of most of them. The major source of controversy is related to the use of the term protalus rampart to designate both a nivo-gravitational landform (also called "pronival ramparts") and a permafrost-related landform. All the considerations presented here allow an active protalus rampart to be defined simply as a (small) active talus rock glacier.

Arvernella microclada Hugonnot & Hedenäs (Amblystegiaceae), a new minute species from France, requiring a separate genus

Arvernella microclada Hugonnot & Hedenäs is described from several localities in the Massif Central of France (Auvergne). This diminutive, autoicous, pleurocarpous moss has strongly prorate distal ends of the leaf lamina cells and straight and erect inner perichaetial leaves. It bears a superficial resemblance to small Heterocladium Bruch & Schimp. species, especially H. flaccidum (Schimp.) A.J.E.Sm. or weak phenotypes of H. wulfsbergii I.Hagen. Other small confervoid species, like Platydictya jungermannioides (Brid.) H.A.Crum or Serpoleskea confervoides (Brid.) Loeske differ in several respects, most notably in the absence of abaxial leaf lamina cell prorations, but also in rhizoid topography (Platydictya) and leaf orientation and leaf margin denticulation (Serpoleskea). Arvernella microclada grows in subalpine tall-herb communities and Fagus sylvatica L. mountain woods on small lava blocks on cold, unstable, and steep scree slopes. The restricted known geographical distribution may be of conservation concern.

Engineering Characteristics of Talus and its Influence Imposed on Tunneling

The special geological conditions of talus are often encountered in southwest China, it brings a lot of difficulties to tunnel construction. The formation mechanism and developmental properties of talus are analyzed in this paper. Based on field investigation on talus diseases, the hazard to tunnel engineering induced by talus and its corresponding measures are also analyzed. The results can be used for the safe and fast construction of tunnels which go through talus deposit.