ICG2022-18

Tropical mountainous regions are commonly identified as landslide hotspots with particularly vulnerable populations. Anthropogenic factors are assumed to play a role in the occurrence and impact of landslides in these populated regions, yet the relative importance of these human-induced factors remains poorly documented. In this work, we explore the impact of forest cover dynamics, agricultural land management practices, urbanisation, roads, and mining/quarrying activities on the occurrence of landslides and their associated risk in the North Tanganyika–Kivu Rift, an area that stretches at the border of four countries in Africa. Using a holistic approach that combines extensive fieldwork, optical and SAR/InSAR satellite remote sensing, time-series analysis, UAS image acquisition, historical photograph processing, citizen science and geomorphic marker understanding, our study demonstrates the role of human activities on the frequency, size and deformation patterns of landslides in the region, in both rural and urban environments. The interaction between uplift associated with the continental rifting in the region, fluvial incision, and the (human-induced) landslides are also key elements that are considered in our analysis. Overall, we highlight the need to consider the human context when studying hillslope instabilities in regions under anthropogenic pressure.

How to cite: Dewitte, O., Depicker, A., Maki Mateso, J.-C., Bielders, C., Deijns, A., Dewaele, S., Govers, G., Jacobs, L., Kanyiginya, V., Kervyn, F., Kervyn, M., Kubwimana, D., Mugaruka Bibentyo, T., Nzolang, C., Sibomana, P., Twongyirwe, R., Vanmaercke, M., and Dille, A.: Landslides in a changing tropical environment: the North Tanganyika–Kivu rift region, Africa, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-164, https://doi.org/10.5194/icg2022-164, 2022.

The eastern Mediterranean is a hotspot in terms of geomorphic hazards, but the activity of gravitational processes in mountainous areas is largely unexplored. Past and present geomorphic activity is key to predicting future risks with respect to hydroclimatic extremes in a changing environment. We carried out dendrogeomorphic research in the Helmos Mountains (Northern Peloponnese, Greece) to determine the timing, spatial extent, and frequency of debris flows and snow avalanches. Specifically, we sampled 492 increment cores from 123 injured Greek firs (Abies cephalonica L.) growing on a debris flow cone and growing along a snow avalanche path. Tree rings were counted and cross-dated with the reference chronology using CooRecorder and CDendro software. The event years were determined based on the location of scars and traumatic resin ducts in the tree rings and by calculating the weighted event-response index (W_It). We further analysed the potential preparatory and triggering climate factors responsible for these events using data from nearby meteorological stations and the ERA5 reanalysis. Debris flow activity was reconstructed from 52 trees, providing a 118-year chronology (1904-2021) with 13 event years and only one severe debris flow occurring in the 1970/1971 dormant period (W_It=148.0), followed by spatially limited records for the 1986/1987 (W_It=3.8) and 1993/1994 (W_It=2.5) dormant periods. The return period of the geomorphically effective events was 9.1 years. Similarly, 71 trees allowed the reconstruction of 12 event years in the period 1854-2021 with one major snow avalanche in 1997/1998 (W_It=304.5) followed by the 1998/1999 event (W_It=6.3). The return period for snow avalanches, including possible events, was 14.0 years. The calculated recurrence intervals of maximum 1-day and 2-day precipitation during a year with severe debris flow (1970/1971) were 1.5-7.6 years and 1.4-13.0 years, respectively. Similarly, other indicators such as maximum monthly precipitation or maximum intensity did not indicate an exceptional rainfall event. We assume a combination of multiple factors including a higher proportion of rainfall at the expense of snow in the winter preceding the event, which allowed saturation of easily erodible moraine deposits in the debris flow source area. In contrast, there are clear climatic indicators of snow avalanche activity in the spring of 1998, when heavy snowfall over three days (62 cm) was followed by rapid snowmelt due to high average temperatures (6-11°C), creating very suitable conditions for snow avalanche activity. We conclude that moderate geomorphic activity that recur on average once every 10-15 years is supplemented by the occasional occurrence of exceptionally large debris flows and snow avalanches depending on the amount and form of winter and spring precipitation. 

How to cite: Tichavský, R., Koutroulis, A., Fabiánová, A., and Spálovský, V.: Occasional but severe: past debris flows and snow avalanches in the Helmos Mts. (Greece) reconstructed from tree-ring records, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-96, https://doi.org/10.5194/icg2022-96, 2022.

A landslide inventory presents a detailed register of the distribution and characteristics of past landslides in a specific area. Landslide inventory maps and other maps such as landslide susceptibility, hazard and risk maps present an essential tool in landslide risk management, supporting authorities, practitioners and decision-makers in the more appropriate and sustainable land planning and risk mitigation strategy development. In recent years, Light Detection and Ranging (LiDAR) data have been commonly used to map landslide morphology and estimate landslide activity. LiDAR is a consolidated remote sensing technique used to obtain digital representations of the topographic surface for areas ranging from a few hectares to thousands of square kilometres. From elevation point clouds obtained by laser scanning, a detailed digital elevation model (DEM) and different DEM derivatives, such as slope, hillshade or contour maps, can be produced. In this study, a historical landslide inventory map of the Hrvatsko Zagorje area (NW Croatia), interpreted from LiDAR high-resolution DEM (HRDEM) derivates, is presented and analyzed regarding geomorphological characteristics. The study area comprises 20.22 km² of the hilly terrain (88% of the area has slope angles >5°), mostly covered by forests (52%). The area is composed of Triassic carbonate rocks, Miocene clastic sedimentary rocks and soils and Quaternary alluvial soils. LiDAR data for the study area was acquired in the framework of the project „Methodology development for landslide susceptibility assessment for land-use planning based on LiDAR technology (LandSlidePlan)“ financed by the Croatian Science Foundation. The topographic derivative datasets used to interpret the landslide morphology were hillshade maps, slope maps and contour lines. Landslide identification on the LiDAR HRDEM derivatives (0.3 m resolution) was manual and GIS-assisted, based on recognizing landslide features (e.g., concave main scarps, hummocky landslide bodies and convex landslide toes). The mapping was performed at a large scale (1:100–1:500) to ensure the correct delineation of the landslide boundaries. Totally 912 landslides were mapped. The total area of mapped landslides is 0.408 km², or 2.02% of the study area, and the mean landslide density is 45.1 slope failures per square kilometre. The average landslide area is 448 m² (median = 173 m²). The small size of the landslides is probably the result of geological conditions (mainly Miocene marls covered with residual soils) and geomorphological conditions, where the differences between the valley bottoms and the top of the hills are rarely higher than 100 meters. Geomorphological characteristics of mapped landslides were compared with characteristics of the stable terrain using different DEM derivatives, such as roughness and curvature. According to the analyses, roughness and curvature values are distributed differently in landslides and stable terrain. Knowledge of the difference between the geomorphological characteristics of landladies and stable terrain provides valuable information for the automatic mapping of landslides and potently unstable slopes.

How to cite: Krkač, M., Bernat Gazibara, S., Sinčić, M., Lukačić, H., and Mihalić Arbanas, S.: Geomorphological characteristics of landslides in the Hrvatsko Zagorje (NW Croatia), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-410, https://doi.org/10.5194/icg2022-410, 2022.

The scale and intensity at which human actions induces Land Degradation depends on which drivers are at play. Land management practices may provide the conditions for increasing or decreasing erosional processes, carbon emissions, water carrying capacity and vegetation cover, while Land Use Change (LUC) determines the spatial extent and magnitude of its effects. In Southern Portugal, especially the Eastern side of the Guadiana River, shallow and incipient soils, a semi-arid Mediterranean-type climate, and land use intensity all contribute to an important degree of degradation. Abrupt LUC can be traced back to the early 20^th century when the commons were divided to be privately exploited on a yearly basis (1906-1926). Then, the autarkic policies of the Estado Novo Dictatorship converted large areas of poor soils to very intensive rainfed wheat crops (1929-1938), which culminated in vast areas of degradation and decreasing yields. The decades that followed were marked as a transitional period where some tenants were still trying to produce rainfed crops while others were converting towards pastures. As Portugal became a member of the EU and thus a partner in the common market, agricultural policy has since 1986 been a major driver for LUC and its effects in soils and productivity. This study used soil erosion data for different land uses from the Vale Formoso Soil Erosion Centre plots, a long data series (1961-Present), field observations and remote sensing data from the Landsat Series (1984-2021) are used to analyse changes in land use, vegetation cover and soil erosion from 13 sample areas within the Mértola Municipality. Results show a very high variability in erosion rates between land use classes, and a tendency towards volatility in change over time that has been exacerbated after the implementation of the Common Agricultural Policy of the EU. Finally, we present a conceptual model describing the temporal variability in erosion processes, discriminating their behaviour at hillslopes and valley floors and within land use / land cover changes, as well as an analysis of its consequences on the study area.

How to cite: Cerqueira, H., Roxo, M. J., and Calvo-Cases, A.: Agricultural Policy triggers Land Degradation in the dry Mediterranean Southern Alentejo, Portugal (1986-2021), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-292, https://doi.org/10.5194/icg2022-292, 2022.

Soil erosion is one of the hillslope processes that receives considerable attention by geomorphologists. Recently, also subsurface erosion by soil piping has become increasingly recognized. So far, the studies have been focused on the importance of soil piping in hydrological and geomorphological processes, and factors controlling piping processes. Nowadays, the Anthropocene brings the environmental changes and society depends on soil more than ever before, so the traditional studies of soil erosion processes need to be redefined. We identify new possible areas of research: (i) soil pipes and pipe collapses (PCs) as natural hazards, (ii) role of soil piping in carbon cycle, (iii) soil pipes and PCs and their relationships with biodiversity, and (iv) piping–affected areas as geodiversity sites. Natural hazards driven by soil piping are land subsidence and degradation, landslides, flooding and off-site sediment effects. Their better recognition will be a step towards better prevention and control measures in piping-affected areas. Moreover, in the context of the Global Change, soil loss due to piping may lead to carbon loss as piping dynamics is affected both by land use and land cover changes as well as climate change. Soil pipes and PCs are closely interlinked with biodiversity, both positively and negatively. On the one hand, piping erosion may directly and indirectly destroy vegetation and animals. On the other hand, in some cases it may create new habitats and provide favourable conditions for some species. Interestingly, we can see piping erosion as the contributor to the world geodiversity, which is clearly observed in badland sites. Summarizing, piping erosion may have a significant impact on environment and society, so this is a time to address and discuss new questions in erosion studies.

The research has been supported by a grant from the Priority Research Area “Anthropocene” under the Strategic Programme Excellence Initiative at the Jagiellonian University and by the Spanish MANMOUNT (PID2019-105983RB-100/AEI/10.13039/501100011033) project funded by the MICINN-FEDER.

How to cite: Bernatek-Jakiel, A. and Nadal-Romero, E.: Can piping erosion impact environment and society? Identifying new research gaps, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-464, https://doi.org/10.5194/icg2022-464, 2022.

The Himalayan Mountain range is infested by natural disasters annually. Mass movement and hillslope instability are among the most common phenomenon witnessed in those regions. The propensity to such activities is perplexing since it is not attributed to a definitive factor. The reason being the complex geological condition of this mountain range, topography, aided by anthropogenic intervention. A number of landslides reported in these regions are often rainfall induced landslides. However, there is always an interplay of geomorphology and tectonics which contribute to such mass movement.

On September, 2017, a colossal landslide occurred along the char Dham (Hindu pilgrimage) corridor, located near Wazri (locally called Ojari) village in Uttarakhand (India). Resulting in the blockade of road for four consecutive days and stranding ~1313 pilgrims of the Char Dham Yatra, and as many as 14 villages were cut-off from the main district headquarters. In order to evaluate the landslide, slope stability, runout, structural, and precipitation analysis were carried out for both the pre- and post- failure event. In the pre-failure analysis, results showed that the maximum shear strain of about 0.16-0.26 was developed parallel to the slope and a total displacement of about 1.8-8 m was likely to take place, parallel to the slope. In the post-failure analysis, results indicated that the maximum shear strain had decreased to 0.14, with a decrease in total displacement to 4.4m. Indicating that much strain was still accumulated in the existing slope. This still implied that the slope was unstable and had accumulated much load on the slope, with high chance of further failure. This model was testified by the incident in the consecutive year of July 11, 2018, where the landslide was triggered due to incessant rainfall. Resulting in the disruption of the daily traffic and stranding ~90 pilgrims of the Char Dham Yatra. The debris flow simulation of the loose unconsolidated material, in case of excessive rainfall effect, revealed a flow accommodating 7-24 m height, 3-4 m/sec velocity, and 100-800 kPa pressure along the Yamuna River. To analyze the role of deformation in the landslide, the study area was subdivided into three distinct zones; (i) fault core, (ii) fault damage zone, and (iii) the intact zone (undeformed host rock), following the evidence from fields. From the visual observations, it was evident that the landslide was confined to the Main Central Thrust (MCT) damage zone.

How to cite: Jamir, I., Kumar, V., Kumar Ojha, A., and Gupta, V.: An appraisal of Pre- and Post-failure regimes of a hillslope using stability, runout, and structural implications; A case study from the NW Himalaya, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-185, https://doi.org/10.5194/icg2022-185, 2022.

We have mapped more than 400 major landslides (debris slides, rockfalls, and rock avalanches) in 5 fluvial valleys in Himalaya (India) between 77.3° E - 80.5° E longitudes. Field/high- resolution satellite imagery based landslide area mapping and field based landslide thickness approximation were used to determine landslide area and volume. Area-volume scaling exponents of these landslides revealed a lateral variation in the study area implying that landslide slopes in the eastern part  of the study area retain relatively less volume that increases towards western part of the study area. We have hypothesized that such lateral variation is possibly caused by lateral variation in the landslide occurrence that in turn is mostly caused by lateral variation in the seismic-climatic regimes.  

Following the hypothesis, we noted that rainfall, surface runoff, soil moisture, and air moisture (climatic variables) data of years 1982-2020 represent a general decrease laterally from east to west in the study area. Further, the role of  topography on the climate variables is also noted as it increases from east to west.  Earthquake (Mw=>4) distribution (1960-2020), Arc Parallel Gravity Anomaly (APGA), cumulative seismic moment, shear stress accumulation rate, and convergence (India-Eurasia) rate  (Seismic variables) also represent a general decrease laterally from east to west in the study area.  The climatic variability is attributed to the spatial variability of the Indian Summer Monsoon (ISM), whereas seismic variability is referred to the spatial variability in the subsurface pattern of the Main Himalayan Thrust (MHT). Thus, such variability in the seismic-climatic regimes is noted to support our hypothesis.   

How to cite: Kumar, V., Jamir, I., Sundriyal, Y., Havenith, H.-B., Gupta, V., Melo, R., Chauhan, N., Gupta, S. K., and Rana, N.: Landslide scaling relationship and its seismic-climatic implications, Himalaya, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-1, https://doi.org/10.5194/icg2022-1, 2022.

How to cite: Sengupta, A. and Nath, S. K.: Static and Dynamic Slope Stability Analysis for locating Critical Slip Surface in Gangtok, Sikkim-Himalaya, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-355, https://doi.org/10.5194/icg2022-355, 2022.

In Nunavik, northern Quebec, Canada, ongoing climate change disturbs the nival regime. The study of deposits on talus underlines the predominance of snow avalanches as the main contributor to present-day slope development. In Tasiapik valley, close to the village of Umiujaq (56°32'35"N, 76°27'43"W), several automatic time-lapse cameras are operating year-round since 2017 along with VDTSILA weather station since 2012. The set of cameras enables monitoring target sections of the slope. The recorded snow avalanches correspond to slab and loose snow avalanches; many are triggered by the collapse of the ridgeline snow-cornices. The most active snow-avalanche season corresponds to late spring (June), when wet snow avalanches occurred after rain-on-snow events and rapid temperature rise, being then in contact with the regolith, therefore responsible of debris transfer downslope. However, the longest runout distance snow avalanches occur during the winter time, in April, after sudden temperatures changes or heavy snowfall. However, by comparing the snow-avalanche activity from other slopes (lake Wiyâshâkimî, 56°16'43"N, 74°27'48"O and Kangiqsualujjuaq, 58°41'33"N, 65°57'32"O) equipped with the same monitoring system, great variations appear in snowfall amount, snowdrift accumulation and triggering factors, sketching the role of continentality and latitude. In addition, in the vicinity of newly established villages due to the forced settlement of indigenous populations, snow avalanches represent a worrying hazard.

How to cite: Decaulne, A., Bhiry, N., Jérémy, G., and Beatriz, F.: Snow avalanches as the main geomorphic active process on hillslopes in Nunavik, Canada, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-26, https://doi.org/10.5194/icg2022-26, 2022.

The development of erosional features in rockwalls indicate the transition from back-wearing (parallel retreat) erosion to down-wearing by linear dissection. Following Rapp (1960), erosional features such as chutes and funnels are the results of successive undermining rockfalls released by thawing after frost damage. The process doesn’t start from the top of the slope but over a scar leave by a large magnitude rockfall which can appear anywhere on the rock face. Sauchyn et al. (1998) suggest that the type of erosional features (chutes, funnels, open cirques) is under structural control in stratified sedimentary rock. Other, like Dunne (1990), Laity & Malin (1985), Lipar & Ferk (2015) or Duszyński et al. (2016) attributes the development of erosional features and the subsequent development of amphitheatre valley heads to underground erosion by subsurface flow. The presence of perennial spring in erosional features on the flysch rockwalls of the northern Gaspé Peninsula (Eastern Canada) suggest that these notches may be the result of seepage erosion. However, observations show that groundwater seeps out the scar of large magnitude rockfalls. If the location of the spring is conditioned by geological and structural setting, the development of erosional features may as well be under geological and structural control. To support these premises and the development of a conceptual model of erosional features formation, a detailed geological, hydrogeological and climatological characterization was carried out. Meteorological instruments, including temperature probes inserted inside horizontal borehole, were installed directly on a rockwall. Four observation wells were drilled on the plateau above the rockwall and around an erosional features. The hydraulic conductivity was determined using pneumatic slug tests performed every 1.6 meters in the boreholes. The hydraulic gradient was calculated from continuous measurements of the water table using water level logger. An optical borehole televiewer, a three-art caliper probe, an induction conductivity probe and a gamma ray detector were also used to support the geological and structural analysis of the rock mass. A structural analysis was also performed on the surface of the rockwall. The results show that the elevation and the location of the spring on the rockwall is not conditioned by a permeability contrast between geological units, the presence of a perched water table or by a network of interconnected fractures channels water. Our result show that groundwater simply reaches the rockwall surface in the erosional feature. At the periphery of the notch, the hydraulic head decreases significantly in the highly weathered and fractured rock layer near the rockwall surface. Depending on the winter severity, seasonal freeze thaw cycles reaches three to five meters deep into the rockwall. Water seepage and ice formation in the erosion notch maintain the rock temperature above 0^oC during winter. Large magnitude rockfalls mainly occur in spring after thawing and groundwater supply near the rockwall surface. The initiation and the development of erosional features in flysch formations appear to be controlled through the interaction between groundwater inflow near the surface of the rockwalls and the meteorological conditions that drive frost weathering.

How to cite: Gauthier, F., Chouinard, C., and Birien, T.: Seepage erosion and escarpment retreat in flysch formation under mid-latitude cold climate, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-172, https://doi.org/10.5194/icg2022-172, 2022.

Long-term analyses of landslide patterns and triggering factors, covering several decades of continuous data, including periods of both acceleration and stability, are a key to understanding landslide activity, background, and variability. This study focused on the long-term relationships between landslide activity and the triggering factors, precipitation in particular, for three landslides in the Western Carpathians, Poland (temperate climate conditions of Central Europe). We determined the activity and triggers for the studied slopes based on dendrochronological reconstruction covering 68 years (1951–2018), including tree-ring eccentricity and compression wood dating for 107 Norway spruce trees. Through statistical comparison between the dendrochronological record of landslide activity and meteorological data (based on daily precipitation totals), we established types and seasons of precipitation that are critical for triggering landslide activity. We found regional similarities but also significant local differences between the three studied slopes. We were able to explain the origin of the differences through the individual features of landslide topography and structure, such as the depth of the shear zones, disintegration of landslide blocks resulting in a plastic, flow-like movement of the material, and location of the landslide blocks in relation to high groundwater levels in the valley floors. Finally, we determined the optimal sequences of triggers leading to heavy landsliding for each slope, therefore establishing the regimes of their activity. Furthermore, we used the same methodological approach on a landslide located in a highly seismic and monsoon area in the Hengduan Mountains, Sichuan, China, where we also revealed the pattern of landslide-precipitation dependence. Based on these results, we argue that the long-term regularities in landslide response to triggers can be generalised into regimes, as is commonly done with river discharge, groundwater levels, and their hydro-meteorological background. We propose establishing “regimes of landslide activity” that are based on decades of observations and reconstructions. Our study demonstrates that such a long-term approach can be an efficient tool for describing and explaining the variability of landslide activity and hazards over space and time.

How to cite: Wistuba, M., Malik, I., Gorczyca, E., and Ślęzak, A.: Establishing regimes of landslide activity – Analysis of landslide triggers over the previous seven decades (Western Carpathians, Poland), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-639, https://doi.org/10.5194/icg2022-639, 2022.

During the construction of the power plant Tušimice 50 years ago, a sludge reservoir was built as one of its auxiliary structures. The sludge pit, barred by 50 m high earthen dam filled fully a valley of Vysočany brook, left-side tributary of Hutná brook. As the sludge pit was gradually filled up during the operation of the powerplant (1980ies-2004). However, already since 1980ies, the activity of landslides at the N slopes of Hutná valley increased. Numerous springs and marshes developed on the slope, and fresh reactivations of the landslides damaged part of the Hořetice village and the local road between Hořetice and Vysočany. The persisting activity of the landslides was documented by numerous reports and papers throughout 1980ies and 90ies (Rybář 1984, Rybář 1987, Nováková 1990, Zika et al. 1991, Rybář 2001).

            Since 2020, the team of dpt. of Engineering geology has performed a complex study on the site trying to document the lasting activity and reveal its causes even almost 20 years after the closing of the power plant. The employed methods included geomorphological and engineering geological mapping, site documentation, vast geophysical survey, aerial photogrammetry using both visible spectrum and IR cameras, hydrological measurements and documentation, and study of borehole and geological documentation.

The mapping was aiming to observe the current activity of the landslide, document spatial changes of the individual landslides compared to previous research, locate the springs and swamps, using GPS devices to ascertain the position of the landforms. Photographic documentation of landforms (scarps, drainage objects, damaged road, etc) and occasional soil probes were dug to observe the bedrock composition. Geophysical survey consisted of 12 profiles across and along the slope, covering its whole extent. The aerial survey allowed construction of a detailed, actual DEM (though occasionally obscured by high vegetation) and orthophotomap, and the IR aerial photos were used for observing wetter areas on a special orthophotomap. Finally, the hydrological measurements of the discharge of Hutná brook were performed to observe water inflow from the studied slope.

The study confirmed that landslides are still active. They have obviously changed and developed since the last mapping in 2001, and numerous findings indicate persisting activity, including documented fresh scarps, inclined trees, broken and dislocated vertical drainage elements, etc.

The cause of the persisting activity of the slope processes is the combination of valley slope, structural-lithological settings and seeping of sludge basin water through permeable sandy layers in the underlying sedimentary complex. As the underground water level increased with the filling of the dam, the water could reach the N slope of the Hutná valley. This was anticipated already before the operation of the sludge basin and confirmed during operation (Nováková 1990), which lead to construction of a drainage system in part of the slope. However, the drainage is slowly ceasing to work due to silting and deterioration, thus allowing the water seep into the slope again.

How to cite: Hartvich, F., Tábořík, P., Klimeš, J., Blahůt, J., and Stemberk, J.: Multidisciplinary study of a 40-year landslide history: who or what caused the reactivation?, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-453, https://doi.org/10.5194/icg2022-453, 2022.

Thousands of large (> 2 ha) rock slope failures affect the Neogene marine sedimentary cover rocks of Aotearoa New Zealand. These slope failures are known to damage lifeline infrastructure, entire suburbs, agricultural land, and deliver substantial volumes of fine sediment to rivers. Despite their prevalence in the landscape and potential impacts, there has been little systematic quantification of their activity, causes, and impact. This research brings together several local case-studies and regional statistical & monitoring analyses that document the causes, movement patterns, and economic and environmental impacts of such rock slope failures in New Zealand’s North Island. At the local scale, for several large landslides that have affected infrastructure and farming operations we present i) financial damage estimates, ii) movement data collected using GPS, time-lapse, and remote-sensing methods, and iii) sediment delivery loads estimated from several independent methods. At the regional scale, for hundreds of large landslides mapped across a region of the North Island, we iv) assess movement patterns using remote-sensing (InSAR and satellite pixel-tracking), v) present a regional-scale statistical analysis of the key landscape parameters explaining the spatial distribution of their occurrence and state of activity; and vi) estimate regional-scale sediment contributions to catchment sediment loads. From the local case studies, we found that: i) individual landslides can impose hundreds of thousands of dollars of damage and seriously hinder infrastructure and farming operations; ii) can move at rates of 10^-2 to 10¹ m per year (or fail catastrophically) with movement patterns strongly influenced by fluvial erosion; and iii) deliver tens of thousands of tonnes of sediment annually. At the regional scale, we found that iv) approximately 9 % of the ~730 mapped large landslides have been actively moving over the past several years; v) low slope angle, fluvial incision and dip slopes most strongly explain the distribution of all landslides, whereas low slope angle and rainfall best explain the distribution of the active landslides; and vi) the active landslides contribute 10 – 30 % of modelled catchment sediment loads (despite representing only 0.2 % of the total area of these catchments). Our findings suggest that large rock slope failures within the marine sedimentary rocks of Aotearoa New Zealand are a significant, but hitherto poorly recognised, hillslope erosion process, source of fine sediment to rivers, and natural hazard. Moreover, our analyses demonstrate an intimate connection between hillslope and fluvial processes, with rivers influencing slope destabilisation across multiple scales and as an efficient receiver of landslide sediment.

How to cite: McColl, S., Williams, F., and Fuller, I.: Hillslope-channel coupling, hazards, and environmental impacts of large landslides in the marine sedimentary rocks of Aotearoa New Zealand., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-489, https://doi.org/10.5194/icg2022-489, 2022.

A relative rarity of large rockfall events makes relevant statistical analysis of the potential meteorological influencing factors extremely difficult. Opposite, small rockfall events occur daily and are well evidenced by the state infrastructure agency. In one year, 2.623 such small rockfall events were evidenced along the 2.348 km long road network of the Republic of Slovenia. A dense network of 280 national meteorological stations provided daily weather data for the analysis of the correlation between rock falling events and weather conditions. We present the results of the extensive statistical analysis of the rockfall data and analyse the impact of the basic meteorological parameters, such as temperature oscillation and precipitation evidenced at the nearest meteorological station, on the occurrence of small-scale rock falling on the national scale.  

How to cite: Šegina, E. and Jemec Auflič, M.: Impact of basic weather conditions on rock falling, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-337, https://doi.org/10.5194/icg2022-337, 2022.