Conventional and UAV-Based Aerial Surveys for Long-Term Monitoring (1954–2020) of a Highly Active Rock Glacier in Austria

Rock glaciers are creep phenomena of mountain permafrost. Speed-up has been observed on several rock glaciers in recent years and attributed to climate change. Although rare, related long-term studies are nevertheless essential to bring a climate perspective to creep velocity changes. In the present study, we focused on changes both in the surface creep velocity and volume of the Leibnitzkopf rock glacier (Hohe Tauern Range, Austria) in the period 1954–2020. We applied 3D change detection using aerial images of both conventional (12 epochs between 1954 and 2018) and unmanned aerial vehicle (UAV)-based aerial surveys (2 epochs, 2019 and 2020), and combined this with ground and air temperature data. Photogrammetric processing (structure-from-motion, multi-view stereo) of the multi-temporal dataset resulted in high-resolution digital orthophotos/DOPs (5–50 cm spatial resolution) and digital elevation models/DEMs (10–50 cm grid spacing). Georeferencing was supported by five externally triangulated images from 2018, bi-temporal aerial triangulation of the image data relying on stable ground around the rock glacier, measured ground control points (2019 and 2020), and measured camera locations (PPK-GNSS) of the UAV flight in 2020. 2D displacement vectors based on the multi-temporal DOPs and/or DEMs were computed. Accuracy analyses were conducted based on geodetic measurements (2010–2020) and airborne laser scanning data (2009). Our analyses show high multi-annual and inter-annual creep velocity variabilities with maxima between 12 (1974–1981) and 576 cm/year (2019–2020), always detected in the same area of the rock glacier where surface disintegration was first observed in 2018. Our volume change analyses of the entire landform for the period 1954–2018 do not indicate any significant changes. This suggests little permafrost ice melt and/or general low ice content of the rock glacier. Analyses of the temperature data reveal a close relationship between higher temperatures and rock glacier acceleration despite the high probability of low ice content. This suggests that hydrogeological changes play an important role in the rock glacier system. The paper concludes with a summary of technical improvements and recommendations useful for rock glacier monitoring and a general view on the kinematic state of the Leibnitzkopf rock glacier

Length changes of Austrian glaciers in 2016/2017

Glacier length change data of 96 Austrian glaciers were collected for the period summer/autumn 2016 to summer/autumn 2017 (variable periods depending on specific measurement dates). The 95 monitored glaciers are well distributed over the glaciated mountain ranges of the Austrian Alps and consider both small and some of the largest (c.15 km²) glaciers in Austria. Therefore, this sample is considered to be representative for all present-day glaciers in Austria. The monitored glaciers spatially extend from latitude 46°33'N to 47°30'N and longitude 10°04'E to 13°39' E. The data made available here comprise the glacier-length-change results for the glaciological year 2016-2017 and are based on a paper published in the official magazine of the Austrian Alpine Club named "Bergauf" (https://www.alpenverein.at/bk/bergauf/bergauf2018/Bergauf_2_2018/). These data are also stored in the database of the World Glacier Monitoring Service (WGMS) in Zurich, Switzerland (https://wgms.ch/). Glacier changes at the 96 glaciers was measured in two different ways. First, at 71 Austrian glaciers, the position of the glacier terminus was quantified for 2016 and 2017 by measuring the distance between distinct marked points in the proglacial area and the ice margin in clearly defined directions (azimuths). The difference of measured distances in 2016 and 2017 yields the glacier length change for one specific point. By calculating the arithmetic mean of several of such marked points at a given glacier, the glacier change value was obtained for this glacier. Second, at seven Austrian glaciers the position of the glacier terminus was quantified for 2016 and 2017 using Global Navigation Satellite System (GNSS) techniques or other geodetic instruments measuring the glacier terminus for both years and - based on this – calculating a glacier length change value. Furthermore, for five glaciers the change of the glacier position was qualitatively determined by photograph comparison. Finally, for 13 glaciers it was not possible to quantify glacier change rates for 2016-2017 due to missing data. The measurements were carried out by 20 different teams led by one or two investigators. Regarding the wider context, glacier length changes of Austrian Glaciers are measured annually within the framework of a monitoring program of the Austrian Alpine Club for more than 100 years. Measurements of length variations in Austria were started as early as 1878 at, for instance, Pasterze Glacier. Since that year, glaciological surveys have been carried out almost annually at this glacier representing one of the longest time series of continuous glacier monitoring worldwide. For more details regarding the glacier monitoring program of the Austrian Alpine Club visit https://www.alpenverein.at/portal/museum-archiv/gletschermessdienst/index.php (only in German)

Length changes of Austrian glaciers in 2017/2018

Glacier length change data of 96 Austrian glaciers were collected for the period summer/autumn 2017 to summer/autumn 2018 (variable periods depending on specific measurement dates). The measurements in 2018 have been carried out by 19 different teams led by one or two investigators per team. The 96 monitored glaciers are well distributed over the glaciated mountain ranges of the Austrian Alps and consider both small and some of the largest glaciers (up to ca.15 km²) in Austria. Therefore, this sample is considered to be representative for all present-day glaciers in Austria. The monitored glaciers extend from latitude 46°33'N to 47°30'N and longitude 10°04'E to 13°39' E. The data published here comprise the glacier-length-change results for the glaciological year 2017-2018 and are based on a paper published in the official magazine of the Austrian Alpine Club named Bergauf (https://www.alpenverein.at/bk/bergauf/bergauf2019/Bergauf_2_2019/). The collected data are also stored in the database of the World Glacier Monitoring Service (WGMS) in Zurich, Switzerland (https://wgms.ch/). Glacier changes at the 96 glaciers was measured in different ways. First, at 69 Austrian glaciers the position of the glacier terminus was quantified for 2017 and 2018 by measuring the distance between distinct marked points in the proglacial area and the ice margin in clearly defined directions (azimuths) for both years. The difference of the measured distances in 2017 and 2018 yields the glacier length change for one specific point. By calculating the arithmetic mean of several of such marked points at a given glacier in 2017/2018, the glacier change value was obtained for glaciers with more than one marked point. Second, at seven Austrian glaciers the position of the glacier terminus was quantified for 2017 and 2018 using Global Navigation Satellite System (GNSS) techniques or other geodetic instruments measuring the glacier terminus for both years. Based on these two GNSS data sets, the glacier length change value was calculated for 2017/2018. Third, at eleven sites the glacier retreat was calculated for a period of two (2016/2018) or three (2015/2018) years using the first method described. Fourth, for six glaciers the change of the glacier position was qualitatively determined by photograph comparison. Results of our analysis show that 89 glaciers retreated, and 4 glaciers were stationary (i.e., no significant frontal change). For three glaciers it was not possible to quantify glacier change rates for 2017/2018 due to missing data or inaccessibility. The mean value of the glacier retreat rate of the 76 glaciers measured in 2017 and 2018 was 17.2 m/a. The highest glacier retreat value was 128.2 m/a measured at Viltragen Glacier, Venediger Mountains. Regarding the wider context, glacier length changes of Austrian Glaciers are measured annually within the framework of a monitoring program of the Austrian Alpine Club. This program is one of the longest glacier monitoring programs and runs since 1891. Measurements of length variations in Austria at single glaciers have been started even earlier dating back to 1878 at Pasterze Glacier. Since that year, glaciological surveys have been carried out almost annually at Pasterze Glacier representing one of the longest time series of continuous glacier monitoring worldwide. For more details regarding the glacier monitoring program of the Austrian Alpine Club visit https://www.alpenverein.at/portal/museum-archiv/gletschermessdienst/index.php (only in German)

Length changes of Austrian glaciers in 2020/2021

Glacier length change data of 91 Austrian glaciers were collected for the period summer/autumn 2020 to summer/autumn 2021 (variable period for each glacier depending on specific measurement dates). The measurements in 2021 have been carried out by 19 different teams led by one or two investigators per team. The 91 monitored glaciers are well distributed over the glaciated mountain ranges of the Austrian Alps and consider both small and some of the largest glaciers (up to ca.15 km²) in Austria. Therefore, this sample is considered to be representative for all present-day glaciers in Austria. The monitored glaciers extend from latitude 46°33'N to 47°30'N and longitude 10°04'E to 13°39' E. The data published here comprise the glacier-length-change results for the glaciological year 2020-2021 and are based on a paper published in the official magazine of the Austrian Alpine Club named Bergauf (https://www.alpenverein.at/bk/bergauf/bergauf2022/Bergauf_2_2022). The collected data are also stored in the database of the World Glacier Monitoring Service (WGMS) in Zurich, Switzerland (https://wgms.ch/). Glacier changes at the 91 glaciers was measured in different ways. First, at 70 glaciers the position of the terminus was quantified for 2020 and 2021 by measuring the distance between distinct marked points in the proglacial area and the ice margin in clearly defined directions (azimuths) for both years. The difference of the measured distances in 2020 and 2021 yields the glacier length change for one specific point. By calculating the arithmetic mean of several of such marked points at a given glacier, the glacier change value was obtained for glaciers with more than one marked point. Second, at nine Austrian glaciers the position of the glacier terminus was quantified for 2020 and 2021 using Global Navigation Satellite System (GNSS) techniques, unmanned aerial systems (UAS/drones), or other geodetic instruments measuring the glacier terminus for both years. Based on these two GNSS/UAS/geodetic data sets, the glacier length change value was calculated for 2020/2021. Third, for twelve glaciers the change of the glacier position was qualitatively determined by photograph comparison or two-year glacier length-change data. Results of our analysis show that 84 glaciers retreated, and 7 glaciers remained stationary (i.e., no significant frontal change up to +/- 1m). For three glaciers it was not possible to quantify glacier change rates for 2020/2021 due to missing data. The mean value of the glacier retreat rate of the 79 glaciers measured in 2020 and 2021 was 11.0 m/a (compared to 15.0 m/a in the previous year). The highest retreat value measured was 54.5 m/a at Schlatenkees Glacier, Venedigergruppe (Venediger Mountains). Regarding the wider context of these results: glacier length changes of Austrian Glaciers are measured annually within the framework of a monitoring program of the Austrian Alpine Club. This program is one of the longest glacier monitoring programs and runs since 1891. Measurements of length variations in Austria at single glaciers have been started even earlier dating back to 1879 at Pasterze Glacier. Since that year, glaciological surveys have been carried out almost annually at for instance Pasterze Glacier, Glocknergruppe (Glockner Mountains) representing one of the longest time series of continuous glacier monitoring worldwide. For more details regarding the glacier monitoring program of the Austrian Alpine Club visit https://www.alpenverein.at/portal/museum-archiv/gletschermessdienst/index.php (only in German)

Length changes of Austrian glaciers in 2021/2022

Glacier length change data of 89 Austrian glaciers were collected for the period summer/autumn 2021 to summer/autumn 2022 (variable period for each glacier depending on specific measurement dates). The measurements in 2022 have been carried out by 19 different teams led by one or two investigators per team (altogether 24 team leaders). The 89 monitored glaciers are well distributed over the glaciated mountain ranges of the Austrian Alps and consider both small and some of the largest glaciers (up to ca.15 km²; e.g., Pasterze) in Austria. Therefore, this sample is considered to be representative for all present-day glaciers in Austria. The monitored glaciers extend from latitude 46°33'N to 47°30'N and longitude 10°04'E to 13°39' E. The data published here comprise the glacier-length-change results for the glaciological year 2021-2022 and are based on a paper published in the official magazine of the Austrian Alpine Club named Bergauf (https://www.alpenverein.at/bk/bergauf/bergauf2023/Bergauf_2_2023). The collected data are also stored in the database of the World Glacier Monitoring Service (WGMS) in Zurich, Switzerland (https://wgms.ch/). Glacier changes at the 89 glaciers was measured in different ways. First, at 71 glaciers the position of the terminus was quantified for 2022 by measuring the distance between distinct marked points in the proglacial area and the ice margin in clearly defined directions (azimuths) for both years. The difference of the measured distances in 2021 and 2022 yields the glacier length change for one specific point. By calculating the arithmetic mean of several of such marked points at a given glacier, the glacier change value was obtained for glaciers with more than one marked point. Second, at ten Austrian glaciers the position of the glacier terminus was quantified for 2022 using Global Navigation Satellite System (GNSS) techniques, unmanned aerial systems (UAS/drones), or other geodetic instruments measuring the glacier terminus for both years. Based on these two GNSS/UAS/geodetic data sets, the glacier length change value was calculated for 2021/2022. Third, for eight glaciers the change of the glacier position was qualitatively determined by photograph comparison or two-year glacier length-change data. For three glaciers (Hintereis Ferner, Landeck Kees, Roter Knopf Kees), a two- or three-year value for the glacier retreat was given, as there is no data for 2021. These were not taken into account when calculating the overall mean value. Results of our analysis show that all observed 89 glaciers retreated. For four glaciers it was not possible to quantify glacier change rates for 2021/2022 due to missing data. Monitoring activities were discontinued for one glacier (Bieltal Ferner) due to the lack of a measurable glacier size. The mean value of the glacier retreat rate of the 78 glaciers measured in 2021 and 2022 was 28.7 m/a (compared to 11.0 m/a in the previous year). This is the highest value in the history of the glacier measurement service of the Austrian Alpine Club. The highest retreat value measured was 89.5 m/a at Schlatenkees Glacier, Venedigergruppe (Venediger Mountains). Regarding the wider context of these results: glacier length changes of Austrian Glaciers are measured annually within the framework of a monitoring program of the Austrian Alpine Club. This program is one of the longest glacier monitoring programs and runs since 1891. Regular measurements of length variations in Austria at single glaciers have been started even earlier. Since 1879, glaciological surveys have been carried out almost annually at for instance Pasterze Glacier, Glocknergruppe (Glockner Mountains) representing one of the longest time series of continuous glacier monitoring worldwide. For more details regarding the glacier monitoring program of the Austrian Alpine Club visit https://www.alpenverein.at/portal/museum-archiv/gletschermessdienst/index.php (only in German)

Length changes of Austrian glaciers in 2018/2019

Glacier length change data of 96 Austrian glaciers were collected for the period summer/autumn 2018 to summer/autumn 2019 (variable period for each glacier depending on specific measurement dates). The measurements in 2019 have been carried out by 19 different teams led by one or two investigators per team. The 96 monitored glaciers are well distributed over the glaciated mountain ranges of the Austrian Alps and consider both small and some of the largest glaciers (up to ca.15 km²) in Austria. Therefore, this sample is considered to be representative for all present-day glaciers in Austria. The monitored glaciers extend from latitude 46°33'N to 47°30'N and longitude 10°04'E to 13°39' E. The data published here comprise the glacier-length-change results for the glaciological year 2018-2019 and are based on a paper published in the official magazine of the Austrian Alpine Club named Bergauf (https://www.alpenverein.at/bk/bergauf/bergauf2020/Bergauf_2_2020/). The collected data are also stored in the database of the World Glacier Monitoring Service (WGMS) in Zurich, Switzerland (https://wgms.ch/). Glacier changes at the 96 glaciers was measured in different ways. First, at 78 Austrian glaciers the position of the glacier terminus was quantified for 2018 and 2019 by measuring the distance between distinct marked points in the proglacial area and the ice margin in clearly defined directions (azimuths) for both years. The difference of the measured distances in 2018 and 2019 yields the glacier length change for one specific point. By calculating the arithmetic mean of several of such marked points at a given glacier in 2018/2019, the glacier change value was obtained for glaciers with more than one marked point. Second, at six Austrian glaciers the position of the glacier terminus was quantified for 2018 and 2019 using Global Navigation Satellite System (GNSS) techniques or other geodetic instruments measuring the glacier terminus for both years. Based on these two GNSS data sets, the glacier length change value was calculated for 2018/2019. Third, for eight glaciers the change of the glacier position was qualitatively determined by photograph comparison. Results of our analysis show that 86 glaciers retreated, 5 glaciers remained stationary (i.e., no significant frontal change), and one glacier slightly advanced (+2.2 m/a at Maurerkees Glacier, Glockner Mountains). For four glaciers it was not possible to quantify glacier change rates for 2018/2019 due to missing data, inaccessibility, or snow coverage. The mean value of the glacier retreat rate of the 84 glaciers measured in 2018 and 2019 was 14.3 m/a (compared to 17.2 m/a in the previous year). The highest retreat value was 86.9 m/a measured at Bärenkopfkees Glacier, Glockner Mountains. Regarding the wider context, glacier length changes of Austrian Glaciers are measured annually within the framework of a monitoring program of the Austrian Alpine Club. This program is one of the longest glacier monitoring programs and runs since 1891. Measurements of length variations in Austria at single glaciers have been started even earlier dating back to 1878 at Pasterze Glacier. Since that year, glaciological surveys have been carried out almost annually at Pasterze Glacier representing one of the longest time series of continuous glacier monitoring worldwide. For more details regarding the glacier monitoring program of the Austrian Alpine Club visit https://www.alpenverein.at/portal/museum-archiv/gletschermessdienst/index.php (only in German)

Length changes of Austrian glaciers in 2019/2020

Glacier length change data of 94 Austrian glaciers were collected for the period summer/autumn 2019 to summer/autumn 2020 (variable period for each glacier depending on specific measurement dates). The measurements in 2020 have been carried out by 19 different teams led by one or two investigators per team. The 94 monitored glaciers are well distributed over the glaciated mountain ranges of the Austrian Alps and consider both small and some of the largest glaciers (up to ca.15 km²) in Austria. Therefore, this sample is considered to be representative for all present-day glaciers in Austria. The monitored glaciers extend from latitude 46°33'N to 47°30'N and longitude 10°04'E to 13°39' E. The data published here comprise the glacier-length-change results for the glaciological year 2019-2020 and are based on a paper published in the official magazine of the Austrian Alpine Club named Bergauf (https://www.alpenverein.at/bk/bergauf/bergauf2021/Bergauf_2_2021/). The collected data are also stored in the database of the World Glacier Monitoring Service (WGMS) in Zurich, Switzerland (https://wgms.ch/). Glacier changes at the 94 glaciers was measured in different ways. First, at 74 glaciers the position of the terminus was quantified for 2019 and 2020 by measuring the distance between distinct marked points in the proglacial area and the ice margin in clearly defined directions (azimuths) for both years. The difference of the measured distances in 2019 and 2020 yields the glacier length change for one specific point. By calculating the arithmetic mean of several of such marked points at a given glacier in 2019/2020, the glacier change value was obtained for glaciers with more than one marked point. Second, at seven Austrian glaciers the position of the glacier terminus was quantified for 2019 and 2020 using Global Navigation Satellite System (GNSS) techniques or other geodetic instruments measuring the glacier terminus for both years. Based on these two GNSS data sets, the glacier length change value was calculated for 2019/2020. Third, for eleven glaciers the change of the glacier position was qualitatively determined by photograph comparison. Results of our analysis show that 85 glaciers retreated, and 7 glaciers remained stationary (i.e., no significant frontal change). For two glaciers it was not possible to quantify glacier change rates for 2019/2020 due to missing data. The mean value of the glacier retreat rate of the 81 glaciers measured in 2018 and 2019 was 15.0 m/a (compared to 14.3 m/a in the previous year). The highest retreat value measured was 104.0 m/a at Hornkees Glacier, Zillertaler Alps. Regarding the wider context, glacier length changes of Austrian Glaciers are measured annually within the framework of a monitoring program of the Austrian Alpine Club. This program is one of the longest glacier monitoring programs and runs since 1891. Measurements of length variations in Austria at single glaciers have been started even earlier dating back to 1878 at Pasterze Glacier. Since that year, glaciological surveys have been carried out almost annually at Pasterze Glacier representing one of the longest time series of continuous glacier monitoring worldwide. For more details regarding the glacier monitoring program of the Austrian Alpine Club visit https://www.alpenverein.at/portal/museum-archiv/gletschermessdienst/index.php (only in German)

Second rock glacier inventory (RGI2) of Central and Eastern Austria, link to Shapefile

Rock glaciers are striking features in high mountain environments indicating permafrost conditions during the period of formation and activity. Within the framework of the Alpine-Space-Project PermaNET, a new polygon-based inventory of rock glaciers has been elaborated comprising the alpine areas of central and eastern Austria as part of an inventory covering the entire European Alps. The establishment of the new inventory was primarily based on an existing point-based inventory which was re-evaluated and amplified using currently available orthophotos, different digital elevation models and derivatives thereof. Further topographic information such as for instance elevation of lower and upper limits, maximum length and width, area and activity degree were gathered in an attribute table. All different parameters were analyzed regarding the entire investigation area, differences between the relevant federal provinces of Austria and between the single mountain regions. These regions were distinguished by differences of mainly climate, topography and present glacier extent. As a result, data on altogether 1647 rock glacier polygons or units were gathered in the inventory comprising 1430 monomorphic rock glaciers (rock glacier with one unit/generation) and 98 polymorphic rock glaciers (with two to five distinct units). 1300 rock glacier units have been classified as relict (no permafrost anymore) covering 97.7 km**2 in total, whereas 347 units with a total area of 21.3 km**2 as intact (containing permafrost) ones. The mean lower limit of relict rock glacier units with a mean size of 0.075 km**2 is situated at 2102 m a.s.l.. For the intact ones the respective values are 0.061 km**2 and 2515 m a.s.l.. Interpreting the results leads to the conclusion that the dominance of relict rock glaciers is due to fact that the summit elevations decrease towards the east thus restricting current permafrost occurrence to limited areas. Furthermore, "normal glaciers" still occupy rock glacier favourable sites particularly in central Austria. Intact rock glaciers usually developed over millennia primarily during the Holocene. In contrast, relict rock glaciers began to form during and after the Lateglacial deglaciation of cirques which generally occurred earlier in the east compared to the west of the investigated area. However, slope orientation was relevant for the deglaciation pattern causing formation of older rock glaciers on „warm“ slopes whereas on “cold” slopes rock glaciers are possibly of younger age. Although a comprehensive overview on rock glacier distribution can be given by our study, drawbacks of this study are the varying quality of information sources, the absence of data on surface motion (except for single rock glaciers) and missing absolute dating of rock glacier surfaces

Permafrost in den Alpen: Erscheinungsformen, Verbreitung und zukünftige Entwicklung

Während die Erforschung der Vergletscherung der Alpen und anderer Gebirge auf eine mehr als 150jährige Geschichte zurückblickt, rückte der Permafrost als verborgene Vereisung im Innern von Böden, Schuttmassen und Felsen der Gebirge erst seit den ausgehenden 1970er-Jahren verstärkt in den Fokus und wurde Wissenschaftlich dokumentiert. Für die Veränderungen von Permafrost im Hochgebirge gibt es bis auf wenige Ausnahmen erst seit den 1980er-Jahren verlässliche Messreihen, was die Analyse der Auswirkungen des Klimawandels heute erheblich erschwert. Nach Einschätzungen mehrerer Studien gehören die Permafrostveränderungen im Zuge des Klimawandels in den Hochgebirgen aktuell zu den wichtigsten Einfl ussfaktoren für alpine Naturgefahren