GM4.15

Complex terrain tropical mountainous catchments are typically characterized by intense rainfall events, flash floods and high erosion rates with large variability over short distances. Whilst these processes are known, little quantitative information on the spatiotemporal variability in suspended sediment yield (SY) of African tropical mountain environments is available. Here, we provide such data for two catchments in the Southern Ethiopian Rift Valley characterised by annual rainfall of 700 to 1000 mm concentrated in the rainy season from April to October. In total 6 gauging stations were installed along Elgo (298 km²) and Shafe (191 km²) rivers which have their headwaters in the Gamo Highlands (max. elevation 3500 m) and run into the rift valley lakes of Chamo (1107 m) and Abaya (1169 m), respectively. For each river, a gauging station was installed where they enter the lakes as well as at the apex of extensive alluvial fans that developed in the graben lowlands, enabling to quantify the buffering capacity of the fans. For Elgo, two extra stations in the highlands were installed to monitor downstream changes in SY. At all stations, discharge (Q) was measured at 10-min resolution using a pressure diver during in 2018-2019. Additionally, 1542 samples were taken to measure the suspended sediment concentration (SSC), and these were used to establish sediment rating curves in order to calculate total suspended SY from the continuous discharge records. Observed SSC varies between 0.04 and 111.48 g/l for discharges ranging between 0.005 and 227.20 m³/s, whereas annual SY varies between 1133 and 6373 t/km²/year. Both SSC and SY values are in line with those reported for other highland rivers in Ethiopia and in line with SY values for other tropical mountain catchments in the world. A strong temporal variability in SSC and SY is observed and can be explained mainly due to changes in hillslope sediment supply throughout the seasons. Peak sediment transport is mostly concentrated in the first two months (May to June) of the rainy seasons accounting for about 60% of the total SY of the season. At the start of the rainy season, topsoil is loose because of tillage operations that prepare the soil for cultivation. Furthermore, vegetation cover is at its lowest value. Throughout the rainy season, vegetation cover increases and hence soil erosion and sediment yield declines.  Comparing the SY of the various gauging stations shows that total sediment load increases in downstream direction, up to the apex of the alluvial fans. Whereas agricultural top soil erosion is most important in the upper parts of the landscape, gully erosion and river bank erosion also contribute much sediment in downstream direction. However, total suspended SY delivered to the lake-based gauging stations is 32 to 53% lower compared to the total suspended SY measured at the gauging station situated near the apex of the alluvial fans. This implies that a significant proportion of the sediment load is buffered by the fans and points to an important dis-connectivity between eroding mountains and rift valley lakes.

How to cite: Alemayehu Kasaye, T., Gulie, G., Chen, M., and Verstraeten, G.: Spatial and Temporal Variability in Suspended Sediment Yield for two tropical mountain catchments draining into the Southern Ethiopian Rift Valley., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2007, https://doi.org/10.5194/egusphere-egu21-2007, 2021.

Mechanical weathering by freezing and thermal processes are influenced by climate. Topography modulates this climatic influence due to altitudinal decrease of temperature, modifying insolation due to rockwall aspects and insulation by snow cover. In this study, we (i) quantify rock fracture damage in the field, (ii) monitor rock surface temperature and snow cover, (iii) model frost weathering processes, (iv) quantify fracture kinematics and (v) assess how these processes contribute to rockwall erosion. For this purpose, we conducted measurements on rockwalls with different aspects along an altitudinal gradient ranging from 2,500 to 3,200 m in the Hungerli Valley, Swiss Alps, between 2016 and 2019.

(i) The geology of the Hungerli Valley comprises schisty quartz slate with inclusions of aplite and amphibolite. We conducted Rock Mass Strength (RMS) measurements and used fracture spacing and uniaxial compressive strength (UCS) measurements as proxies for mechanical weathering. RMS ranges from 62 to 77 for schisty quartz slate rockwalls, up to 73 for aplite and 74 for amphibolite. Fracture spacing and UCS reflect lithological differences of the catchment area suggesting a geological control on weathering efficacy. 

(ii) Rock surface temperatures (RST) were monitored using temperature loggers. RST decreases with elevation from 2,500 to 2,900 m, however, increases again at 3,150 m potentially due to higher insolation on ridges. Snow cover duration shows a similar altitudinal trend. Due to aspect, RSTs are 2 to 4 °C warmer on south facing rockwalls with significant shorter snow cover period.

(iii) We used measured RST to drive frost cracking models by Walder and Hallet (1985) and Rempel et al. (2016). Both models show near surface frost weathering at lower altitudes, which should results in lower UCS. The models show significantly higher frost cracking at higher altitudes with peaks at rock depths between 0.5 and 2 m suggesting a higher fracture spacing.

(iv) Rockwalls between 2,500 and 2,900 m were equipped with crackmeters and show higher daily temperature changes and crack deformation at lower altitudes or south facing aspects due to higher insolation compared to higher located rockwalls. Seasonal crack displacement depends on dipping of monitored blocks and is controlled by both thermal and cryogenic processes (Draebing, 2020).

(v) In summary, low-altitudinal rockwalls show a higher weathering at the surface due to a combination of thermal processes and near surface frost weathering resulting in release of small blocks and lower erosion rates. In contrast, rockwalls at higher altitudes reveal higher seasonal thermal changes propagating deeper into the rock in combination with frost cracking in higher depths, which results in larger blocks and higher erosion rates.

Draebing, D.: Identification of rock and fracture kinematics in high Alpine rockwalls under the influence of altitude, Earth Surf. Dynam. Discuss., 1-31, 2020.

Rempel, A. W., Marshall, J. A., & Roering, J. J.: Modeling relative frost weathering rates at geomorphic scales. Earth and Planetary Science Letters, 453, 87-95, 2016.

Walder, J., and Hallet, B.: A Theoretical-model of the fracture of rock during freezing, Geological Society of America Bulletin, 96, 336-346, 1985.

How to cite: Draebing, D. and Mayer, T.: Topographic controls on frost and thermal weathering processes and implications for rockwall erosion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3121, https://doi.org/10.5194/egusphere-egu21-3121, 2021.

Typical cooling joints of granite have been believed to be orthogonal, and characteristic topography of granitic rocks like tors and boulder fields are interpreted in combination with the cooling joints and weathering. However, most of the previous studies were performed by the observation on the ground, and the 3D observation of cooling joints and the topographic features was not sufficient. We observed tors and boulder fields of granitic rocks using UAV and 3D modelling and found that columnar joints are typical for the granite that forms tors and that boulder fields are the accumulations of rock columns as well as boulders made by the spheroidal weathering of rock columns. Tors we observed were Mt. Kinabalu of Borneo, Mt. Mizugaki, Mt. Jizo, Mt. Gozaisho, Mt. Konze and 5 other locations in Japan. We observed that tors consist of polygonal rock columns with undulating joints, more irregularly shaped than the columnar joints of volcanic rocks. The cross-sectional areas of rock columns varied from 1 to 130 m^2, much larger than typical rock columns of volcanic rocks. The rock columns of granite are typically polygonal dipyramids, of which shapes may be dependent on the cooling history of granite. Boulder fields we observed was the Kui boulder fields in Hiroshima. We found that the boulder field is the accumulation of prismatic rock columns as well as rounded rock boulders. The prismatic rock columns had basal cross-sectional areas of 0.8 m^2 on average. The rock columns had chamfering cracks at corners, which are assumed to be made during cooling and to form preliminary outlines of core stones. Core stones had surface crusts or rindlets, which exfoliate and leave more rounded core stones.

  Rainstorm-induced landslides of weathered granite reflect weathering styles of granite: Landslides that occurred recently in Japan had three types, landslides of loosened layers of decomposed granite (or micro-sheeted granite), landslides of core-stone bearing materials, and landslides of saprolite. Landslides with core-stones were particularly destructive because of their inertia. Potential sites of such landslides could be predicted using columnar joints in fresh rocks as a clue.

How to cite: Chigira, M. and Hirata, Y.: Cooling joints of granite as a structural cause of the tors and boulder fields of granite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-528, https://doi.org/10.5194/egusphere-egu21-528, 2021.

Rock fall processes of various size and magnitude control retreat rates of high alpine rock-walls. For millennial time scales, these retreat rates can be quantified in-situ from concentrations of cosmogenic nuclides along bedrock depth profiles (Mair et al., 2019). We measured cosmogenic ³⁶Cl and ¹⁰Be along several such profiles at Mt Eiger in the Central Swiss Alps to study the local rock-wall retreat on this time scale (Mair et al., 2019; 2020). The resulting spatial pattern shows that rock-wall retreat rates are low (0.5 to 0.6 ± 0.1 mm/yr) in the higher region of the NW rock-wall, in contrast to both the lower part of the NW rock-wall and the SE face, where rates are high (1.7 ± 0.4 to 3.5 ± 1.4 mm/yr). We link these retreat rates to differences in local temperature conditions, because the patterns of faults and fractures and the lithology of the bedrock are similar at all sites, and thermo-cryogenic processes are known to weaken the bedrock through fracturing, thereby preconditioning the occurrence of rock fall (e.g., Draebing and Krautblatter, 2019). However, it is still unclear how effective and at which rate individual thermo-cryogenic processes contribute to the preconditioning through fracturing. Therefore, we investigate several processes and estimate the probability of bedrock fracturing through the employment of a theoretical frost-cracking model, which predicts cracking intensity from ice segregation. The model results infer a low efficiency in the higher region of the NW rock-wall, but a relatively high one in the lower section of the NW wall and on the SE rock face of Mt. Eiger. Although the model is rather generic, the results disclose a significant control of temperature conditions on the erosional processes and rates. Furthermore, temperature conditions for the last millennia have been similar to present day conditions, as our reconstructions disclose, therefore the cosmogenic-nuclide-based long-term differences in rock-wall retreat rates predominantly stem from large contrasts in the microclimate between the NW and SE walls of Mt. Eiger. Accordingly, the site-specific differences in microclimate conditions could explain the lower retreat rates in the upper part of the NW rock-wall and the rapid retreat in the SW face and in the lower part of the NW rock face.

References

Draebing, D. and Krautblatter, M.: The Efficacy of Frost Weathering Processes in Alpine Rockwalls, Geophys. Res. Lett., 46, 6516–6524, doi:10.1029/2019GL081981, 2019.

Mair, D., Lechmann, A., Yesilyurt, S., Tikhomirov, D., Delunel, R., Vockenhuber, C., Akçar, N. and Schlunegger, F.: Fast long-term denudation rate of steep alpine headwalls inferred from cosmogenic 36Cl depth profiles, Sci. Rep., 9, 11023, doi:10.1038/s41598-019-46969-0, 2019.

Mair, D., Lechmann, A., Delunel, R., Yeşilyurt, S., Tikhomirov, D., Vockenhuber, C., Christl, M., Akçar, N. and Schlunegger, F.: The role of frost cracking in local denudation of steep Alpine rockwalls over millennia (Eiger, Switzerland), Earth Surf. Dyn., 8, 637–659, doi:10.5194/esurf-8-637-2020, 2020.

How to cite: Mair, D., Lechmann, A., Delunel, R., Yeşilyurt, S., Tikhomirov, D., Vockenhuber, C., Christl, M., Akçar, N., and Schlunegger, F.: High alpine rock-wall retreat rates over millennia through thermo-cryogenic pre-conditioned rock fall (Mt. Eiger, Switzerland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5908, https://doi.org/10.5194/egusphere-egu21-5908, 2021.

Weathering of rock-cut structures exposed to the environment is strongly influenced by fluctuations in climatic variables. Both macro and microclimate data are needed to identify key weathering types and rates likely to affect rock-cut structures in a specific region. The aim of this paper is to study the macro and micro climatic conditions affecting the rock-cut churches in Lalibela, Ethiopia to determine how the climate influences weathering at this site. Macro climate data collected over a 26-year period and microclimate data monitored on the north, east, south and west walls at one of the churches in the Lalibela church complex (Bete Mariam) are used to make these assessments. Microclimate data was monitored during the long rains (Kiremt), short rains (Belg) and dry (Bega) seasons in 2018 and 2019. The results showed a high seasonal variation in macro climatic conditions like rainfall and ambient relative humidity. The micro climatic (rock surface) conditions also tended to vary seasonally. The diurnal range of rock surface temperature during Bega varied significantly depending on which cardinal directions the walls were facing, with south and west facing walls having high diurnal thermal ranges. The influence of aspect was less pronounced in Belg and Kiremt, but cloud cover played an important role in varying the range of diurnal thermal and humidity cycles from day to day during these seasons. These climate trends are likely to cause seasonal variations in wetting and drying cycles, deep wetting, increased time of wetness and thermal cycling. These wetting/drying and heating/cooling characteristics affect weathering processes. During Kiremt, biological weathering, salt weathering and clay swelling are more likely to occur than in Belg and Bega. High diurnal thermal ranges in Bega are likely to cause thermal fatigue in this season. This is the first paper to address the macro and micro climatic trends that influence rock weathering at the rock-cut churches in Lalibela. The results of this study also have implications for rock-cut structures in northern Ethiopia having similar environmental conditions as Lalibela.

How to cite: Taye, B. and Viles, H.: Impacts of climatic seasonality on weathering of rock-cut structures at Lalibela, Ethiopia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16253, https://doi.org/10.5194/egusphere-egu21-16253, 2021.

The supply of fresh minerals to Earth’s surface by erosion is thought to modulate global climate by removing atmospheric carbon dioxide (CO₂) through silicate weathering. In turn, weathering of accessory carbonate and sulfide minerals is a geologically-relevant CO₂ source, which may dampen or reverse the effect of silicate weathering on climate. Although these weathering pathways commonly operate side by side, we lack quantitative constraints on their co-evolution across erosion-rate gradients. Using stream-water chemistry across a 3 order-of-magnitude erosion-rate gradient in shales and sandstones of southern Taiwan, here, we demonstrate that silicate, sulfide, and carbonate weathering are linked: Increasing sulfide oxidation generates sulfuric acid and boosts carbonate solubility whereas silicate weathering kinetics remain constant or even decline, perhaps due to buffering of the pH by carbonates. On timescales shorter than marine sulfide compensation, CO₂ emission rates from weathering in rapidly-eroding terrain are more than twice the CO₂ sequestration rates in slow-eroding terrain. On longer timescales, CO₂ emissions are compensated, but CO₂ sequestration rates do not increase with erosion, in contrast to assumptions in carbon cycle models. We posit that these patterns are broadly applicable to many Cenozoic mountain ranges that expose dominantly siliciclastic metasediments.

How to cite: Bufe, A., Hovius, N., Emberson, R., Rugenstein, J. K. C., Galy, A., Hassenruck-Gudipati, H. J., and Chang, J.-M.: Co-variation of silicate, carbonate, and sulphide weathering drives release of CO2 with erosion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9221, https://doi.org/10.5194/egusphere-egu21-9221, 2021.

The Vosges Mountains in NE France belong to the belt of Variscan massifs located in the foreland of the Alps. Despite its rather limited extension barely reaching 6000 km², this range of low mountains peaking at ~1425 m presents three contrasting primary characteristics. Firstly, a bipartite N-S subdivision can be achieved based on the geological basement: whereas the southern part, traditionally referred to as the crystalline Vosges, is composed of a mosaic of Palaeozoic rocks, including igneous (mostly intrusive and secondarily extrusive), metamorphic, and sedimentary rocks, the northern part is much more homogeneous given its Triassic sandstone cover (“sandstone Vosges”). Secondly, a clear E-W topographic gradient characterises the mountain range. By contrast to the steep hillslopes and elevation drops regularly exceeding 600 m (sometimes reaching 900-1000 m) between the summits and the valley floors on the eastern side (Alsace; south-western border of the Upper Rhine Graben, URG), the western side exhibits more gently-sloping hillslopes along with a longer extension (Lorraine; eastern border of the Parisian Basin). This results from the sharp E-W contrast in Late Cenozoic tectonic activity between sustained subsidence in the URG to the east and weak rock uplift characterising the Parisian Basin to the west. Finally, the imprint left by Quaternary climatic fluctuations yielded a N-S gradient: whereas the southern part (roughly covering 80-90% of the crystalline Vosges) hosted abundant valley glaciers and still bears traces of significant glacial erosion (cirques and U-shaped valleys), the northern part (mostly the sandstone Vosges) was void of ice cover.

In spite of these advantageous characteristics, very little is known about the Quaternary evolution of the massif, in particular regarding the long-term interactions between denudation, lithological control, climatic forcing and tectonic activity. Against this background, this contribution aims to present the first data of long-term, massif-wide denudation. Modern stream sediments from 21 river catchments of different size draining the whole massif were thus sampled for in situ ¹⁰Be concentration measurements at the outlet of their mountainous reach. Catchment-wide denudation rates inferred from cosmogenic ¹⁰Be will be combined with the analysis of morphometric parameters and structural connectivity resulting from the processing of a high-resolution DEM (5 m). Catchment selection was operated according to the threefold subdivision above: i.e. heterogeneous vs homogenous petrography, tectonically-active eastern side vs “quiescent” western side and glaciated vs unglaciated catchments. We thus test the main hypothesis that the four NE, NW, SE, SW quarters of the Vosges massif shall be characterised by contrasting denudation rates, reflecting the respective role played by the controlling factors on long-term denudation. To our knowledge, this contribution is the first attempt to quantify denudation at the massif scale of a European low mountain range. This is especially relevant as long-term landscape evolution in the Variscan belt, by contrast to the numerous works focusing on denudation in high-mountains ranges (e.g. the Alps), has been regularly disregarded in recent geomorphological studies.

*Georges Aumaître, Didier L. Bourlès and Karim Keddadouche

How to cite: Jautzy, T., Rixhon, G., Braucher, R., Schmitt, L., and Team*, A.: Massif-wide denudation of the Vosges Mountains (NE France) inferred from in situ 10Be concentrations in stream sediments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14281, https://doi.org/10.5194/egusphere-egu21-14281, 2021.

The Southern Alps of New Zealand are the expression of the oblique convergence between the Pacific and Australian plates, which move at a relative velocity of nearly 40 mm/yr. This convergence is accommodated by the range-bounding Alpine Fault, with a strike-slip component of ~30-40 mm/yr, and a shortening component normal to the fault of ~8-10 mm/yr. While strike-slip rates seem to be fairly constant along the Alpine Fault, throw rates appear to vary considerably, and whether the locus of maximum exhumation is located near the fault, at the main drainage divide, or part-way between, is still debated. These uncertainties stem from very limited data characterizing vertical deformation rates along and across the Southern Alps. Thermochronology has constrained the Southern Alps exhumation history since the Miocene, but Quaternary exhumation is hard to resolve precisely due to the very high exhumation rates. Likewise, GPS surveys estimate a vertical uplift of ~5 mm/yr, but integrate only over ~10 yr timescales and are restricted to one transect across the range.

To obtain insights into the Quaternary distribution and rates of exhumation of the western Southern Alps, we use new ¹⁰Be catchment-averaged erosion rates from 20 catchments along the western side of the range. Catchment-averaged erosion rates span an order of magnitude, between ~0.8 and >10 mm/yr, but we find that erosion rates of >10 mm/yr, a value often quoted in the literature as representative for the entire range, are very localized. Moreover, erosion rates decrease sharply north of the intersection with the Marlborough Fault System, suggesting substantial slip partitioning. These ¹⁰Be catchment-averaged erosion rates integrate, on average, over the last ~300 yrs. Considering that the last earthquake on the Alpine Fault was in 1717, these rates are representative of inter-seismic erosion. Lake sedimentation rates and coseismic landslide modelling suggest that long-term (~10³ yrs) erosion rates over a full seismic cycle could be ~40% greater than our inter-seismic erosion rates. If we assume steady state topography, such a scaling of our ¹⁰Be erosion rate estimates can be used to estimate rock uplift rates in the Southern Alps. Finally, we find that erosion, and hence potentially exhumation, does not seem to be localized at a particular distance from the fault, as some tectonic and provenance studies have suggested. Instead, we find that superimposed on the primary tectonic control, there is an elevation/temperature control on erosion rates, which is probably transient and related to frost-cracking and glacial retreat.

Our results highlight the potential for ¹⁰Be catchment-averaged erosion rates to provide insights into the magnitude and distribution of tectonic deformation rates, and the limitations that arise from transient erosion controls related to the seismic cycle and climate-modulated surface processes.

How to cite: Roda-Boluda, D., Schildgen, T., Wittmann-Oelze, H., Tofelde, S., Bufe, A., Prancevic, J., and Hovius, N.: Erosion rates of the New Zealand Southern Alps reflect long-term tectonics and transient climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6571, https://doi.org/10.5194/egusphere-egu21-6571, 2021.

Colombia is an equatorial country located in the northwestern corner of South America with characteristic and complex climatic and geologic settings, which contribute to a great diversity of landforms in the Colombian Andes. 65% of the Colombian population is concentrated in this mountainous terrain, where landslides and torrential flows are common. These natural hazards led to several tragic events over time. Their occurrence is favored by a very dynamic landscape made up of weak and highly weathered materials and affected by tectonic stress. In this study, we aim to gain a better understanding of morphometric control on the occurrence of landslides and torrential flows through process geomorphology and information derived from Digital Elevation Models (DEMs). Several morphometric indices related to drainage network, basin geometry, drainage texture, relief characteristics, asymmetry factor and others were calculated over 168 drainage basins in the northern Colombian Andes. We used quantitative geomorphology to find patterns of anomalies associated with landscape evolution and the occurrence of landslides and torrential flows. Understanding morphodynamics from morphogenesis is important to assess landslide and torrential flow hazard conditions in relation to landscape characteristics and evolution, to support hazard assessment, and consequently to reduce human and economic losses.
Keywords: Landslide, torrential flow, morphometric indices, mountainous terrains.

How to cite: Naranjo Bedoya, K., Aristizábal, E., Hölbling, D., García, J., Aguilar, A., and Ortiz, D.: Approach for analyzing landslide and torrential flow hazard conditions in relation to landscape evolution in the northern Colombian Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8508, https://doi.org/10.5194/egusphere-egu21-8508, 2021.

Landslides from mountainous bedrock hillslopes often contain boulders, the presence of which has been shown to influence landscape evolution by altering hillslope geomorphic processes and river erosion. Furthermore, the presence in various proportions of large grain sizes on hillslopes can amplify both landslide and flood hazards in largely unquantified ways. Boulders can have an immediate destructive potential on properties and infrastructure and can hinder response and recovery by blocking access routes, posing a challenge for removal. On entering the river network, they might have far reaching effects if remobilised in high flows, damaging or destroying key infrastructure such as hydropower plants and inducing significant knock-on effects on local economies. A fundamental step towards quantification of increased hazard potential is the understanding environmental controls on boulder production. Despite their potential to enhance hazard, the probability of large boulders being produced within different landslide types has not been directly accounted for in landslide hazard mapping.

Our study focuses on the upper Bhote Koshi catchment, northeast of Kathmandu (Nepal), characterised by extreme topographic gradients, seismicity and monsoonal climate, and subjected to frequent landslides and floods. This, coupled with increased population pressure and infrastructure growth, makes the area prone to natural disasters.

We used high resolution optical imagery to map more than 11300 boulders and analysed this large dataset in combination with lithology and topography, and well as structural and landslide data, to investigate controls on boulder production and grain size distributions in different lithological, structural and geomorphic settings of the landscape.

Lithology appears to exert a significant influence on boulder sizes, with statistically significantly larger boulders observed in crystalline rocks of the Higher Himalaya Sequence than in metasedimentary rocks of the Lesser Himalaya Sequence. We also observe that the spacing of the most pervasive fracture set, parallel to foliation, influences boulder size distributions in some lithologies, whilst other dominant regional fracture sets appear not to strongly correlate with mapped boulder sizes.

Although recent studies have shown the importance of structural control on boulder sizes, our large dataset reveals that for complex, high-relief landscapes, with high erosion rates, fracture characteristics do not fully explain grain size distribution.

The type of processes involved in boulder production and transport on slopes, before reaching the river network, also appears to exert a control over grain size distributions and boulder density, with rockfall processes appearing to be responsible for producing boulders with largest sizes as opposed to rockslides, where the high energy and mode of transport is likely associated with increased fragmentation.  

Analysing lithological and structural characteristics alone may not be sufficient to explain the observed distribution and would thus only give a limited insight in the enhanced hazard levels posed by boulders across different sectors of a landscape and other factors, such as distance from source and mode of transport at shorter temporal scales, must be taken into account.  

How to cite: Dini, B. and Bennett, G. L.: Analysis of controlling factors on boulder production on the hillslopes of the upper Bhote Koshi catchment, Nepal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15605, https://doi.org/10.5194/egusphere-egu21-15605, 2021.