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Multi‐temporal digital terrain models (DTMs) derived from airborne or uncrewed aerial vehicle (UAV)‐borne light detection and ranging (LiDAR) platforms are frequently used tools in geomorphic impact studies. Accurate estimation of mobilized sediments from multi‐temporal DTMs is indispensable for hazard assessment. To study volumetric changes in alpine environments it is crucial to identify and discuss different kind of error sources in multi‐temporal data. We subdivided errors into those caused by data acquisition, data processing, and spatial properties of the terrain. In terms of the quantification of surface changes, the propagation of errors can lead to high uncertainties. Three alpine catchments with different LiDAR point clouds of different origins (airborne laser scanning [ALS], UAV‐borne laser scanning [ULS]), varying point densities, accuracies and qualities were analysed, and used as basis for interpolating DTMs. The workflow was developed in the Schöttlbach area in Styria and later applied to further catchments in Austria. The main aim of the presented work is a comprehensive DTM uncertainty analysis specially designed for geomorphic impact studies, with a resulting uncertainty analysis serving as input for a change detection tool. Our findings reveal that geomorphic impact studies need the careful distinction between actual surface changes and different data uncertainties. ULS combines the benefits of terrestrial laser scanning with all the benefits of ALS. However, the use of ULS data does not necessarily improve the results of the analysis since the high level of detail is not always helpful in geomorphic impact studies. In order to make the different point clouds and DTMs comparable the quality of the ULS point cloud had to be reduced to fit the accuracy of the reference data (older ALS point clouds). Using a point cloud with a high point density with a regular planimetric point spacing and less data gaps, in the best case collected during leaf‐off conditions (e.g., cross‐flight strategy) turned out to be sufficient for our geomorphic research purposes. [ABSTRACT FROM AUTHOR]

Regions with marginal occurrence of discontinuous permafrost are very specific due their transition to non-permafrost conditions at recent times. Knowledge about the potential distribution of permafrost in the past and at present is crucial to understand its characteristics and dynamics as well as inherent processes. This analysis comprises the simulation of the potential distribution of discontinuous permafrost using six scenarios with different temperature depressions in the entire Reisseck Mountains (46°57'N, 13°22'E) for the year 2000 (Sc-2000), the Little Ice Age (Sc-LIA) and four scenarios for the Younger Dryas - locally referred to as Egesen - in the Alpine Lateglacial period (Sc-E1 to Sc-E4). The results were validated at two different spatial scales; at a regional scale for the entire study region Reisseck Mountains, Central Austria, with data from the distribution of relict and intact rock glaciers; at a local scale for the study area Hintereggengraben Valley - Hohe Leier with data from five years of continuous ground temperature monitoring using data from eight automatic miniature temperature dataloggers. Past conditions were simulated using the year 2000 as a basis for the lower limits of permafrost occurrence. A depression in the mean annual temperature of -1.4 K was used for modelling permafrost conditions during the LIA. Potential permafrost distribution in the Younger Dryas was modelled with temperature depression of -2.5 to -4.0 K compared to the LIA. Our results show a spatial distribution of 9.94 km² (3.1 %) in the sce- nario 2000 to 134.57 km² (42.1 %) in the scenario Sc-E4. The simulations of the thermal conditions in the Younger Dryas validated with the locations of the relict rock glacier suggest scenario Sc-E1 as the most probable. This implies a mean annual temperature depression of -2.5 K compared to LIA and depression of the lower limit of permafrost of ca. -560 m compared to the year 2000. A few relict rock glaciers are located in much lower areas and can therefore be stated as formed in pre-Egesen stages. As a further palaeoclimatical consequence we assume that all inactive rock glaciers in the Reisseck Mountains were still active in the LIA. [ABSTRACT FROM AUTHOR]

Kellerer-Pirklbauer, A., Slupetzky, H. and Avian, M., 2012. Ice-avalanche impact landforms: the event in 2003 at the glacier Nördliches Bockkarkees, Hohe Tauern Range, Austria. Geografiska Annaler: Series A, Physical Geography, 94, 97-115. doi:10.1111/j.1468-0459.2011.00446.x ABSTRACT The hanging glacier Nördliches Bockkarkees (47° 07′ 21″ N; 12° 44′ 00″ E) represents the only Austrian glacier that formed large and hazardous ice avalanches over the last decades. Only one major ice avalanche was released between August 1993 and July 2011 underlying the rareness of such large ice avalanches in the Austrian Alps. The ice avalanche happened on 26 June 2003 and was very unusual for two reasons: First, the ice avalanche occurred suddenly without major signs of glacier instabilities even a few days before the event. Second, the ice avalanche was released very early in the season. Ice and debris with a volume of 300 000 m3 avalanched over a vertical distance of 1200 m. The main deposits with a volume of 250 000 m3 and a debris content of 10% formed a flat avalanche cone in the Käfer Valley covering 82 000 m2. This paper focuses on geomorphic and glaciological field measurements and observations at and below the ice avalanche deposit and its vicinity after the event. Studies were made (a) at the deposited material itself, (b) at the reshaped land surface below the deposit after ice melt, (c) at the front and margin of the deposit, and (d) outside the deposit. Our study reveals different types of ice-avalanche impact landforms comparable to landforms caused by snow avalanches. It is shown that ice avalanches charged with debris at the Nördliches Bockkarkees are important in forming and reshaping erosional and depositional landforms along the track. However, the conservation potential of these landforms is low. [ABSTRACT FROM AUTHOR]

Kellerer-Pirklbauer, A., Lieb, G.K.,Avian, M. and Carrivick, J., 2012. Climate change and rock fall events in high mountain areas: numerous and extensive rock falls in 2007 at Mittlerer Burgstall, Central Austria. Geografiska Annaler: Series A, Physical Geography, 94, 597ndash;78. doi:10.1111/j.1468-0459.2011.00449.x Abstract Landslides in alpine areas are becoming more frequent. In 2007, a number of rock fall events occurred on the sharp SE-ridge of the mountain Mittlerer Burgstall (2933 m a.s.l., 47° 06′ 07″ N; 12° 42′ 36″ E) completely changing the shape of the mountain. Before the events, the SE-ridge was sharp with steep rock faces on both sides. The mountain was a nunatak surrounded by two glacier tongues of Pasterze Glacier during the Little Ice Age. In this paper we use geomorphological mapping, permafrost distribution modelling, glacier reconstruction, surface and near-surface ground temperature data, air temperature data, and airborne laserscanning data to assess these multiple rock fall events. Results show that the entire area of detachment covers 3100 m2. The areas of transportation and deposition cover 85 000 m2 partly contributing to the supraglacial debris cover of Pasterze Glacier. The volume of all rock fall deposits is about 56 000 m3. Permafrost modelling and ground temperature monitoring indicate that the area of detachment is located near the lower limit of discontinuous permafrost. Permafrost is relatively warm and thin at the summit area of Mittlerer Burgstall with a mean temperature of only -1.0°C at 1.8 m depth in 2007-2010. Substantial surface lowering of the glacier tongues surrounding the mountain on both sides (by −250 and −70 m since the Little Ice Age) changed the stress and strain field in the bedrock. Furthermore, the generally highly fractured bedrock favoured slope instability. The triggering event for the rock falls were most likely the effects of the warm winter of 2006/07 which was 2.2-4.8°C warmer compared to the seven winters before. A monitoring programme regarding future rock falls at Mittlerer Burgstall is ongoing. [ABSTRACT FROM AUTHOR]

Long-term observations of partly debris-covered glaciers have allowed us to assess the impact of supra-glacial debris on volumetric changes. In this paper, the behaviour of the partially debris-covered, 3.6 km2 tongue of Pasterze Glacier (47°05′N, 12°44′E) was studied in the context of ongoing climate changes. The right part of the glacier tongue is covered by a continuous supra-glacial debris mantle with variable thicknesses (a few centimetres to about 1 m). For the period 1964–2000 three digital elevation models (1964, 1981, 2000) and related debris-cover distributions were analysed. These datasets were compared with long-term series of glaciological field data (displacement, elevation change, glacier terminus behaviour) from the 1960s to 2006. Differences between the debriscovered and the clean ice parts were emphasised. Results show that volumetric losses increased by 2.3 times between the periods 1964–1981 and 1981–2000 with significant regional variations at the glacier tongue. Such variations are controlled by the glacier emergence velocity pattern, existence and thickness of supra-glacial debris, direct solar radiation, counter-radiation from the valley sides and their changes over time. The downward-increasing debris thickness is counteracting to a compensational stage against the common decrease of ablation with elevation. A continuous debris cover not less than 15 cm in thickness reduces ablation rates by 30–35%. No relationship exists between glacier retreat rates and summer air temperatures. Substantial and varying differences of the two different terminus parts occurred. Our findings clearly underline the importance of supra-glacial debris on mass balance and glacier tongue morphology. [ABSTRACT FROM AUTHOR]

The Hinteres Langtalkar rock glacier (Gössnitztal, Hohe Tauern, Austria) has been part of a complex transportation system of debris and ice since the beginning of the Holocene and shows the highest creep rates of all rock glaciers measured in the Hohe Tauern Range. Results of movement analysis show that the entire rock glacier behaves very differently at different zones and that sudden temporal and spatial changes of velocity rates are a typical feature. Zones with high rates occur close to rather inactive zones and zones with low rates have rapidly accelerated within recent years. The increase in movement rates over time is probably caused by topography. These studies – especially the measurement of surface velocities and elevational changes – allow a differentiation of the rock glacier and a first attempt of a morphogenetic interpretation. In this context, it is important that the innermost part of the cirque was covered by a small cirque glacier during the Little Ice Age advance. This cirque glacier created a moraine complex which contributes to the material supply of the rock glacier. A first estimation of transportation rates is possible with the help of the measurement results available, leading to an estimation of a probable age of at least 4000 years. [ABSTRACT FROM AUTHOR]

Earth observation offers a variety of techniques for monitoring and characterizing geomorphic processes in high mountain environments. Terrestrial laserscanning and unmanned aerial vehicles provide very high resolution data with high accuracy. Automatic cameras have become a valuable source of information—mostly in a qualitative manner—in recent years. The availability of satellite data with very high revisiting time has gained momentum through the European Space Agency's Sentinel missions, offering new application potential for Earth observation. This paper reviews the status of recent techniques such as terrestrial laserscanning, remote sensed imagery, and synthetic aperture radar in monitoring high mountain environments with a particular focus on the impact of new platforms such as Sentinel-1 and -2 as well as unmanned aerial vehicles. The study area comprises the high mountain glacial environment at the Pasterze Glacier, Austria. The area is characterized by a highly dynamic geomorphological evolution and by being subject to intensive scientific research as well as long-term monitoring. We primarily evaluate landform classification and process characterization for: (i) the proglacial lake; (ii) icebergs; (iii) the glacier river; (iv) valley-bottom processes; (v) slope processes; and (vi) rock wall processes. We focus on assessing the potential of every single method both in spatial and temporal resolution in characterizing different geomorphic processes. Examples of the individual techniques are evaluated qualitatively and quantitatively in the context of: (i) morphometric analysis; (ii) applicability in high alpine regions; and (iii) comparability of the methods among themselves. The final frame of this article includes considerations on scale dependent process detectability and characterization potentials of these Earth observation methods, along with strengths and limitations in applying these methods in high alpine regions. [ABSTRACT FROM AUTHOR]

Valley glaciers in the European Alps are rapidly receding at present and in many cases show signs of glacier disintegration. This highly dynamical glacial-proglacial transition zone might include debris-covered ice bodies of various dimensions. In case of valley overdeepenings lakes form in the proglacial area related to glacier recession, glacier surface lowering or by melting of the debris-covered ice bodies in the proglacial area. Glacier surface lowering in combination with glacier recession cause the flooding of the glacier margin in the basin forming a glacier-lateral to supraglacial lake. We observed several large-scale ice-floating events between September 2016 and October 2018 at such a supraglacial lake adjacent to the largest glacier in Austria (Pasterze Glacier). The originally presumed proglacial lake seems to be rather a supraglacial lake covering large amounts of glacier ice, which steadily disintegrates forming icebergs. Multiple data were used to better understand the processes acting at this glacial-proglacial transition zone: Time-lapse camera images with a sub-daily temporal resolution (2016-2018) covering the area of interest give insight into acting processes. Differential GPS was used mapping the superficial glacier boundary for the period 2003-2018. Digital terrain models derived from terrestrial laser scanning (2010-2018) and unmanned aerial systems/UAS (2016-2018) as well as orthophotos also derived from UAS (2016-2018) were analysed to quantify lake and glacier extent as well as landform changes. Several ERT-profiles measured in the proglacial area between 2015 and 2018 (n=16) revealed massive ice lenses and extensive ice layers exceeding 20 m in thickness covered by different types of sediments. Automatic weather station and ground temperature data give further insight in the thermal characteristics of the area of interest. We conclude the following stages of process development at Pasterze Glacier: (a) rapid glacier recession into a basin overdeepend by the glacier; (b) glacial and glacio-fluvial sedimentation in the glacial-proglacial transition zone covering parts of the glacier or dead ice in the basin; (c) initial formation and enlargement of the glacier-lateral to supraglacial lake by steady melting and surface lowering of the glacier ice and debris-covered dead ice; (d) disintegration of glacier ice at the lake bottom or at the surface influenced by high water pressure along fractures showing signs of tilting, sudden disintegration and formation of icebergs; (e) steady melting of the floating icebergs accompanied by tilting events. The latter two stages are also relevant for tourists in the area because small-scale tsunami-like waves have been formed by such processes submerging the lake shore. [ABSTRACT FROM AUTHOR]

Rock glaciers are capable of storing water in solid (permafrost ice) as well as in liquid form (groundwater within the unfrozen base layer). The latter is relevant no matter the actual state of the rock glacier (intact, containing ice versus relict, no more ice present). A nation-wide comparison of the water equivalent of glacier ice within the Austrian Alps is conducted to evaluate the role of rock glaciers in the hydrological cycle at its current state and potentially in the future. Estimates of ice volumes and their uncertainties, especially related to thickness estimates of permafrost-ice bodies, are discussed in the light of available data and need to be seen as order-of-magnitude estimates. With intact rock glaciers covering almost 123 km 2 and an assumed ice content of 40% within the permafrost body, ice volumes are estimated to be 0.93 Gigatons. This corresponds to 8.3% of the ice volume estimated for the most recent glacier inventory of the Austrian Alps. Thus, with the currently available data, a water equivalent ratio of ~1: 12 for rock glacier ice versus glacier ice is estimated. In addition to the solid water storage, the dynamic storage potential within rock glaciers in liquid form needs to be considered. While this volume is relatively small compared to the ice volume in glaciers and rock glaciers (ratio of ~1: 20), the time-scales of hydrological relevance (when they become runoff due to ice melt) are very different. This dynamic liquid water storage is replenishable and therefore available over shorter time scales (seasonal drainage pattern), and moreover relatively stable and may potentially even slightly increase as pore space becomes available due to increased melting of permafrost ice. In the light of climate warming and projected glacier recession, the relative hydrological importance of rock glaciers as water stores (in solid as well as in liquid form) in the European Alps is expected to increase and their storage-discharge patterns need to be accounted for in water management considerations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)