Assessing the ecological value of dynamic mountain geomorphosites

Geoheritage is a component of geodiversity constituted by all the elements of geodiversity recognized by society for their particular values. The definition of these values, including the importance of geoheritage for biodiversity, plays a key role in the process of heritage recognition and geoconservation policymaking. In mountain environments, dynamic geomorphosites have a strong influence on plant diversity because the active geomorphological processes responsible for their formation act as renovators for habitats of pioneer species. In this paper, we propose criteria to assess the ecological value of dynamic mountain geomorphosites. We show that the interest of plant communities (species richness and presence of rare or protected species) and the influence of geomorphological processes on plant communities (disturbances, surface movement and soil) are fundamental criteria for assessing the ecological value in an exhaustive and objective way and that the question of the scale (local and national scales) is also a crucial parameter. We then illustrate this methodological proposal by evaluating the ecological value of three dynamic geomorphosites and a talus slope in the western Swiss Alps.

Study on blasting vibration response mechanism of talus slope based on particle discrete element model

Talus slope are widely distributed all over the world, which is a special natural landscape and widely distributed in southwest and Northeast China particularly. It’s formed by the collapse and transportation of parent rock, freeze-thaw cracking and other reasons, so it’s often loosely accumulated at the foot of the hillside or at the gentle hillside. They are usually composed of collapsed rockfalls and weathered soil mixtures with large particle sizes. Therefore, Tunnel excavation construction through blasting will directly threaten the construction and operation safety of Railway, Highway and other projects along the way, which is very easy to cause heavy economic and personnel losses. In order to explore the dynamic response mechanism of overlying loose talus slope affected by blasting construction, taking the blasting excavation of Daqianshiling talus slope as an example, we measured the size of rocks on the slope on site, carried out the on-site and indoor geotechnical tests, and monitored the velocity and acceleration in real time. Then, we constructed the two dimensional particle discrete element model of irregular rock under blasting, which calibrated based on macro mechanical parameters obtained from field measurements. On this basis, we studied the process of rock breaking by blasting, the dynamic response law of slope, the propagation law of stress wave reflected and an interesting phenomena, eddy current phenomenon, by the the numerical simulation. Finally, we verified the applicability and limitation of Sadovsky family formulas for talus slope under blasting. This research is conducive to controlling blasting parameters and safe construction.

Spectral Induced Polarization imaging to investigate an ice-rich mountain permafrost site in Switzerland

Spectral induced polarization (SIP) measurements were collected at the Lapires talus slope, a long-term permafrost monitoring site located in the Western Swiss Alps, to assess the potential of the frequency dependence (within the frequency range of 0.1–225 Hz) of the electrical polarization response of frozen rocks for an improved permafrost characterization. The aim of our investigation was to (a) find a field protocol that provides SIP imaging data sets less affected by electromagnetic coupling and easy to deploy in rough terrains, (b) cover the spatial extent of the local permafrost distribution, and (c) evaluate the potential of the spectral data to discriminate between different substrates and spatial variations in the volumetric ice content within the talus slope. To qualitatively assess data uncertainty, we analyze the misfit between normal and reciprocal (N&R) measurements collected for all profiles and frequencies. A comparison between different cable setups reveals the lowest N&R misfits for coaxial cables and the possibility to collect high-quality SIP data in the range between 0.1–75 Hz. We observe an overall smaller spatial extent of the ice-rich permafrost body compared to its assumed distribution from previous studies. Our results further suggest that SIP data help to improve the discrimination between ice-rich permafrost and unfrozen bedrock in ambiguous cases based on their characteristic spectral behavior, with ice-rich areas showing a stronger polarization towards higher frequencies in agreement with the well-known spectral response of ice.

Inferring rock glacier genesis and dynamics from age-layer modelling and borehole age-profile

<p>The genesis of rock glaciers differs fundamentally from ‘normal’ glaciers and results in much older landforms that are often reaching ages of several millennia. Recent datings of rock glacier material from boreholes indicate early Holocene ages for rock glaciers and allow the derivation of age-depth profiles at the borehole location. We use here a 2-dimensional numerical modelling approach that calculates age-layers (isochrones) within the rock glacier body and that considers the accretion, melt and flow-advection of rock glacier material. We apply this model to the case of Lazaun rock glacier (Southern Ötztal Alps) for which a well dated profile from a borehole exists, with ages at the bottom older than 9000 years (Krainer et al. 2015). With our modelling we are able to reproduce the observed age-depth profiles well and are able to infer a long-term accumulation rate that is around 1 cm/yr which is an order of magnitude higher than a previous estimate that does not account for deformation. The modelling is consistent with the classic rock glacier genesis of material accretion in the upstream talus slope and confirms the dominance of deformation in the shear-zone at the bottom layer of the rock glacier.<br>We conclude that combining age-layer modelling with dated depth-profiles of rock glaciers allows for important new insights into our understanding of rock glacier evolution and dynamics.</p><p>REFERENCES  <br>Krainer, K., Bressan, D., Dietre, B., Haas, J., Hajdas, I., Lang, K. & Tonidandel, D. (2015). A 10,300-year-old permafrost core from the active rock glacier Lazaun, southern Oetztal Alps (South Tyrol, Northern Italy). Quaternary Research, 83 , 324-335. </p><p> </p>

Recent geomorphic destabilization of mountain slopes, a possible link to climate change? Two case studies from Switzerland

<p>Geomorphological destabilisations in high mountain areas are often linked to permafrost degradation and changing precipitation intensities, induced by climate change. Considering the complex interaction between meteorological conditions, geology and topography, two alpine mass movements that took place in 2019 in the canton of Valais (Swiss Alps) were investigated with regard to their possible causes. During three consecutive summers (2017-2019), independent surveys were carried out on a high alpine talus slope at Col du Sanetsch (2100 – 2750 m a.s.l.) and an unstable rock face at Grosse Grabe, Mattertal (2600 – 2700 m a.s.l.), using unmanned aerial vehicle (UAV) and terrestrial laser scanning (TLS). The resulting high-resolution topography allows detecting and quantifying small and large geomorphic changes, such as rock tilting, rockfalls, rockslides, erosion and depositions of rock debris by snow avalanche action, debris channel cutting and fill and debris flow deposits. In both study areas, the summer of 2019 was characterized by mass movement events of greater magnitude than the geomorphic activity measured in the summers before.</p><p>At Grosse Grabe, the rock face was observed by webcam imagery since 2011, in the background of a rock glacier, which was initially the main object of survey. Isolated rock falls started in January 2017, launching a more accurate survey of the rock face by TLS in July 2017. In the next two summers, the entire unstable part of the rock wall, 70 m high, had been tilting at an increasing rate (1 to 3.3 cm/month). From mid-July until the end of October 2019, consecutive large rock fall events (up to > 10,000 m<sup>3</sup>) lead to the complete collapse of the monitored rock face (5000 m<sup>2</sup>), with a total volume of more than 60,000 m<sup>3</sup>. After the collapse of this heavily fractured, south facing rock face, the long-lasting wet rockfall scar indicated the presence of thawing permafrost ice. Beside the geological characteristics, which are favouring the rock wall instability, the consequences of the multi-decennial significant warming of the permafrost is presumably an implicated factor.</p><p>On the talus slope (2 km<sup>2</sup>) that was surveyed at Col du Sanetsch, a large debris flow event (ca. 20,000 m<sup>3</sup> spread over multiple debris flow channels) was observed in the evening of 11 August 2019. Most of the mobilized sediments originated from incision of the talus apex area, while only a small part came from intermediate debris storage within rock wall gullies. An analysis of historical aerial photographs shows that the total displaced volume during the 2019 event exceeds each historical debris flow event that occurred on the talus slope since 1946.</p><p>In contrast to Grosse Grabe, where weather conditions have played no role on the development of the instability, the debris flow event at Col de Sanetsch is linked to an intense prefrontal supercell, causing rainfall intensities between 10 and 25 mm/h, in some places in less than 15 minutes. As such events are presumed to become more frequent with climate change, more debris flow events of this type can be expected in the future.</p>