Rapid Evaluation of Sediment Budgets

Abstract. In order to get a better understanding of the future
development of alpine slope-type debris flows in the frame of climate
change, complete and gapless records of the last century for this type of
geomorphologic process are necessary. However, up to now such records have been
scarce. Here, the slope-type debris flow activity in Horlachtal, Austria,
has been investigated since 1947 with the help of historic and recent area-wide
remote sensing data. Using geomorphological mapping, both spatial and
temporal variabilities in debris flow dynamics can be shown. The results
indicate short-term variations rather than consistent increasing or
decreasing trends of slope-type debris flow activity in Horlachtal.
Specifically, three active periods between 1954 and 1973, 1990 and 2009, as
well as 2015 and 2018, can be registered. Analyses of the deposited
debris flow volumes show that for parts of the study area the largest
volumes appeared in the early 1990s, which might have even influenced the
dynamics in the following years. Studies on the spatial variabilities
revealed differences of slope-type debris flow activity within the study
area and point to local rainfall events as triggers. However, long-term
precipitation data of high temporal resolution of two alpine meteorological
stations do not reveal increasing or decreasing trends in the occurrence of
such events.


Spatio-temporal analysis of slope-type debris flow activity in Horlachtal, Austria, based on orthophotos and lidar data since 1947

Abstract. Since the end of the Little Ice Age (LIA) in the middle of the 19th century, Alpine glaciers have been subject to severe recession that is
enhanced by the recent global warming. The melting glaciers expose large
areas with loose sediments in the form of lateral moraines, amongst other forms. Due to their instability and high slope angle, the lateral moraines are reworked by geomorphological processes such as debris flows, slides, or fluvial erosion. In this study, the development of the morphodynamics and changes in geomorphological processes on lateral moraines were observed over decades, based on a selection of 10 glacier forefields in the Eastern Alps. To identify geomorphological changes over time, several datasets of archival aerial images reaching back to the 1950s were utilized in order to generate digital elevation models (DEMs) and DEMs of difference. The aerial images were complemented by recent drone images for selected moraine sections, enabling a high-resolution analysis of the processes currently occurring. The results concerning the development of morphodynamics on lateral moraine sections are diverse: some slopes display a stagnation of the erosion rates, whereas the rates of one section
increase significantly; however, the majority of the slopes show a decline in morphodynamics over decades but stay on a high level in many cases. In particular, moraine sections with high morphodynamics at the beginning of the observation period mostly show high erosion rates up until present-day measurements, with values up to 11 cm yr−1. These moraine sections also feature heavy gullying on their upper slopes. A correlation between the development of morphodynamics and the time since deglaciation could scarcely be established. In fact, the results instead indicate that characteristics of the lateral moraines such as the initial slope angle at the time of deglaciation have a significant influence on the later morphodynamics. These observations raise concerns as to whether the until now often conducted
analyses based on the comparison of lateral moraine sections with different distances to the glacier terminus, assumed to represent varying time spans since deglaciation, can provide sound evidence concerning the process of
stabilization.


Development of the morphodynamics on Little Ice Age lateral moraines in 10 glacier forefields of the Eastern Alps since the 1950s

Aerial photographs of the European Alps usually only reach back to the middle of the 20th century, which limits the time span of corresponding studies that quantitatively analyse long-term surface changes of proglacial areas using georeferenced orthophotos. To the end of the Little Ice Age, this leads to a gap of about 100 years. Using digital monoplotting and several historical terrestrial photographs, we show the quantification of surface changes of a Little Ice Age lateral moraine section until the late second half of the 19th century, reaching a total study period of 130 years (1890–2020). The (initial) gully system expands (almost) continuously over the entire study period from 1890 to 2020. Until 1953, the vegetation-covered areas also expanded (mainly scree communities, alpine grasslands and dwarf shrub communities), before decreasing again, especially between 1990 and 2003, due to large-scale erosion within the gully system. Furthermore, our results show that the land-cover development was impacted by temperature and precipitation changes. With the 130-year study period, we contribute to a substantial improvement in the understanding of the processes in the proglacial by analysing the early phase and thus the immediate response of the lateral moraine to the ice exposure.

/pdf/quantitative-long-term-monitoring-1890-2020-of-morphodynamic-30tvjoke.pdf

Quantitative Long-Term Monitoring (1890–2020) of Morphodynamic and Land-Cover Changes of a LIA Lateral Moraine Section

Glaciers, known as solid reservoirs, are important water supply sources in northwest China. In this paper, mineral dust collected from a Chinese alpine mining area (Beizhan iron mine) and an ice cube (with a 225 cm2 section and a volume of 1000 mL) were employed via a delicate physical experiment to study the ablation of glaciers covered by mineral dust in alpine regions. After that, the ablation mechanism was revealed using the energy conservation theory. The main findings are as follows: (1) When the solar radiation intensity is 993 W/m2, the glacier ablation rate increases by 13.9% (from 282 to 321.2 mL/h) as the mineral dust coverage rate increases from 0% to 42.7%. (2) When the mineral dust coverage rate remains at 30%, the glacier ablation rate increases by 11.6% (from 291.8 to 325.78 mL/h) as the solar radiation intensity increases from 1007 to 1153 W/m2. (3) When the solar radiation intensity and mineral dust coverage rate remain unchanged, the ablation rate of the glacier covered by the mineral dust inversely increases with the dust particle size. The ablation rates of the particle size gradings C, B, and A (the dust particle sizes of gradings A, B, and C in 0.0375–0.075 mm, 0.075–0.125 mm, and 0.125–0.25 mm accounted for 5%:50%:45%, 30%:40%:30%, and 70%:30%:0%, respectively) were 293.4, 301.2, and 305.6 mL /h, respectively, and the corresponding ablation rates increased by 2.7% and 1.5%. (4) The smaller the average particle size of the mineral dust, the greater the contribution to the ablation rate; a 1 °C temperature increase to the glacier ablation rate is equivalent to 29.1%, 33.6%, and 40.6% increases in dust coverage for particle size classes C, B, and A. (5) The mineral dust covering the glacier surface could not only reduce the reflectivity of the glacier surface to solar radiation but could also continuously transfer the absorbed radiant energy and its own chemical energy to the glacier body, accelerating the glacier’s meltwater speed. The findings of this paper can provide the necessary theoretical basis for mineral dust control and glacier water conservation in alpine mining areas.

/pdf/study-on-the-ablation-of-the-glacier-covered-by-mineral-dust-3gy5o5i0.pdf

Study on the Ablation of the Glacier Covered by Mineral Dust in Alpine Regions

Since the end of the Little Ice Age (LIA), formerly glaciated areas have undergone considerable changes in their morphodynamics due to external forces and system-internal dynamics. Using multi-temporal high-resolution digital elevation models (DEMs) from different remote sensing techniques such as historical digital aerial images and light detection and ranging (LiDAR), and the resulting DEMs of difference (DoD), spatial erosion and accumulation patterns can be analyzed in proglacial areas over several decades. In this study, several morphological sediment budgets of different test sites on lateral moraines and different long-term periods were determined, covering a total period of 49 years. The test sites show high ongoing morphodynamics, and therefore low vegetation development. A decrease as well as an increase of the mean annual erosion volume could be demonstrated at the different test sites. All test sites show a slope–channel coupling and a decrease in the efficiency of sediment transport from slopes to channels. These developments are generally subject to conditions of increasing temperature, decreasing short-term precipitation patterns and increasing runoff from adjacent mountain streams. Finally, the study shows that sediment is still available on the investigated test sites and the paraglacial adjustment process is still in progress even after several decades of deglaciation (~133 years).

Long-Term Changes of Morphodynamics on Little Ice Age Lateral Moraines and the Resulting Sediment Transfer into Mountain Streams in the Upper Kauner Valley, Austria

. Alpine rivers have experienced considerable changes in channel morphology over the last century. Natural factors and human disturbance are the main drivers of changes in channel morphology that modify natural sediment and flow regimes at local, catchment, and regional scales. In glaciated catchments, river sediment loads are likely to increase due to increasing 15 snow and glacier melt runoff, facilitated by climate changes. Additionally, channel erosion and depositional dynamics and patterns are influenced by sediment delivery from hillslopes, and sediment in the forefields of retreating glaciers. In order to reliably assess the magnitudes of the channel-changing processes and their frequencies due to recent climate change, the investigation period needs to be extended to the last century, ideally back to the end of the Little Ice Age. Moreover, a high temporal resolution is required to account for the history of changes in channel morphology and for better detection and 20 interpretation of related processes. The increasing availability of digitized historical aerial images and advancements in digital photogrammetry provides the basis for reconstructing and assessing the long-term evolution of the surface, both in terms of planimetric mapping and the generation of historical digital elevation models (DEMs). The

Evolution of an Alpine proglacial river during seven decades of deglaciation quantified from photogrammetric and LiDAR digital elevation models

. Since the end of the Little Ice Age (LIA) in the middle of the 19 th century, Alpine glaciers have been subject to severe recession that is enhanced by the recent global warming. The melting glaciers expose large areas with loose sediments, amongst others in the form of lateral moraines. Due to their instability and high slope angle, the lateral moraines are reworked by geomorphological processes such as debris flows, slides or fluvial erosion. In this study, the development of the 10 morphodynamics and changes of geomorphological processes on lateral moraines were observed over decades, based on a selection of 10 glacier forefields in the eastern Alps. To identify geomorphological changes over time, several datasets of archival aerial images reaching back to the 1950s were utilized in order to generate DEMs and DEMs of difference. The aerial images were complemented by recent drone images for selected moraine sections, enabling a high-resolution analysis of the processes currently occurring. The results concerning the development of morphodynamics on lateral moraine sections are 15 diverse: some slopes display a stagnation of the erosion rates, the rates on one section increase significantly and the majority of the slopes show a decline of the morphodynamics over decades, which, however, stay on a high level in many cases. In particular, moraine sections with high morphodynamics in the beginning of the observation period mostly show high erosion rates up until now with values up to 11 cm per year. These moraine sections also feature heavy gullying on their upper slopes. A correlation between the development of morphodynamics and the time since deglaciation could scarcely be established. In 20 fact, the results rather indicate that characteristics of the lateral moraines such as the initial slope angle at the time of deglaciation have a significant influence on the later morphodynamics. These observations results of this study and previous studies are due to the fact that the latter used space-for-time substitution instead of an observation over longer time periods. Using space-for-time substitution for the study

Sarah Betz-Nutz

Papers

Long-Term Changes of Morphodynamics on Little Ice Age Lateral Moraines and the Resulting Sediment Transfer into Mountain Streams in the Upper Kauner Valley, Austria

Spatio-temporal analysis of slope-type debris flow activity in Horlachtal, Austria, based on orthophotos and lidar data since 1947

Development of the morphodynamics on Little Ice Age lateral moraines in 10 glacier forefields of the Eastern Alps since the 1950s

Evolution of an Alpine proglacial river during seven decades of deglaciation quantified from photogrammetric and LiDAR digital elevation models

Development of the morphodynamics on LIA lateral moraines in ten glacier forefields of the Eastern Alps since the 1950s