Andreas Kellerer-Pirklbauer

THE RESPONSE OF PARTIALLY DEBRIS-COVERED VALLEY GLACIERS TO CLIMATE CHANGE: THE EXAMPLE OF THE PASTERZE GLACIER (AUSTRIA) IN THE PERIOD 1964 TO 2006

Abstract. 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.

CLIMATE CHANGE AND ROCK FALL EVENTS IN HIGH MOUNTAIN AREAS: NUMEROUS AND EXTENSIVE ROCK FALLS IN 2007 AT MITTLERER BURGSTALL, CENTRAL AUSTRIA

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. 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 ma.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 85-000m2 partly contributing to the supraglacial debris cover of Pasterze Glacier. The volume of all rock fall deposits is about 56-000m3. 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.

Schmidt-hammer exposure-age dating (SHD) of rock glaciers in the Schöderkogel-Eisenhut area, Schladminger Tauern Range, Austria

Schmidt-hammer rebound values (R-values) enable relative-age dating of landforms, with R-values relating to degree of weathering and therefore length of exposure. This method – recently termed as Schmidt-hammer exposure-age dating (SHD) – was applied to date five rock glaciers (size range, 0.01–0.12 km2) and one recent rockfall deposit at the study area Schöderkogel-Eisenhut, in the Schladminger Tauern Range (14°03′E, 47°15′N), Austria. The rock glaciers consist of gneiss or high metamorphic series of mica-schist that are comparable in their R-values. Four of them are relict (permafrost absent) and one is intact (containing patches of permafrost). On each of the five rock glaciers, SHD was carried out at 4–6 sites (50 measurements per site) along a longitudinal transect from the frontal ridge to the root zone. Results at all five rock glaciers are generally consistent with each other sharing statistically significant R-values along transects. The range between the highest and the lowest mean R-value at each of the five rock glaciers is 9.9–5.2. Using rock glacier length and surface velocity data from nearby sites, the rock glacier development must have lasted for several thousand years. Furthermore, by using SHD results from rock glaciers of known age from other sites in the region with comparable geology, approximate surface ages of 6.7–11.4 ka were estimated. This indicates long formation periods for all five rock glaciers. Our results suggest that many of the 1300 relict rock glaciers in central and eastern Austria were formed over a long period during the Lateglacial and Holocene period.

PREFACE: CONCEPTS AND IMPLICATIONS OF ENVIRONMENTAL CHANGE AND HUMAN IMPACT: STUDIES FROM AUSTRIAN GEOMORPHOLOGICAL RESEARCH

Environmental change and human impact are main drivers of change in geomorphological processes and behaviour, especially in mountain systems with a high sensitivity to change and a greater geodiversity (Slaymaker 2010), compared to most other landscapes. According to Turner II et al. (1990) global environmental change may be differentiated between systemic and cumulative environmental changes. Systemic changes take account of physically interconnected phenomena on a global scale, such as hydroclimate and sea level change. In contrast, cumulative changes consider unconnected, local to intermediate-scale processes, namely relief, land cover and land-use changes, but result in a cumulative effect on the global system. For mountain regions the important drivers of environmental change are hydroclimate, relief and land use and therefore these regions are affected by both systemic and cumulative changes (Slaymaker et al. 2009). However, the different drivers are closely connected, therefore, it is challenging to rank their relative importance (Slaymaker 2010). The inter-linkage between atmo-, bio-, hydro-, cryoand lithosphere is crucial for spatial and temporal trajectories in geomorphic systems. Climate and environmental changes are increasingly being identified in the European Alps (e.g. Keiler et al. 2010). Temperature changes in this region have increased at twice the global average rate since the late nineteenth century. Furthermore, precipitation has also increased nonlinearly, with significant regional and seasonal differences, as well as differences by elevation and aspect within the European Alps and its neighbouring regions (Auer et al. 2007; Haeberli et al. 2007; Brunetti et al. 2009). Resulting changes in snow and rainfall have implications for snow cover thickness and duration (which also affect subsurface temperatures), and catchment runoff (Beniston et al. 2003). Furthermore, temperature and precipitation changes can also be linked to changes in glacier mass balance and terminus position, in particular at high elevations (Zemp et al. 2006; Lambrecht and Kuhn 2007; Huss et al. 2008; Steiner et al. 2008). Permafrost monitoring sites throughout the Alps also show changes in alpine permafrost distribution, temperature profiles, active layer thickness and movement changes of rock glaciers (Harris et al. 2003; Delaloye et al. 2008; Noetzli and Vonder Muehll 2010). While the direct effects of the changing hydroclimate on these systems have now been monitored for several decades, the indirect effects on geomorphological processes and on sedimentary systems are less well known. Furthermore, geomorphological processes in high-relief areas are strongly influenced by various interacting factors, for example, slope angle and aspect, weathering characteristics, sediment availability, slope moisture supply and land cover. These processes evolve in a downslope direction, leading to high spatial and temporal variability in the process domain. Moreover, changes of cryospheric systems

Alpine permafrost occurrence at its spatial limits: First results from the eastern margin of the European Alps

Knowledge about the occurrence and distribution of permafrost in marginal regions of the Austrian Alps is currently very limited. As a consequence, a research project has recently been initiated to model and measure permafrost occurrence in the Niedere Tauern Range, Styria. The occurrence and distribution of permafrost in the study area is discussed on the basis of small-scale modelling results as well as large-scale field validation and verification. The first results are presented here. Both implemented regional modelling approaches indicate a very low percentage of probable permafrost occurrence. Field results underline the importance of snow cover characteristics and, in particular, the spatial distribution of coarse debris for permafrost occurrence at its spatial limits. Coarse surface substrate combined with suitable snow cover conditions enable permafrost existence at a mean annual air temperature (MAAT) of 1.6°C at a selected study site. Furthermore, it can be assumed that at least some of the previously thought ‘relict’ rock glaciers in the Niedere Tauern Range are underlain by permafrost at altitudes far below modelled permafrost occurrence.

Velocity Changes of Rock Glaciers and Induced Hazards

Recent observations and geodetic measurements in the European Alps show that changes are occurring on rock glacier dynamics, ranging from moderate velocity variations to strong acceleration or even total collapse. These changes can be related to the ground temperature and to climate warming. In most cases, rock glaciers do not represent any serious hazard, except the instability of their surface and local rockfalls at the steep front. The surface movements, though moderate, can nevertheless cause damages to sensible infrastructures like cableways or buildings, if these are not designed to adapt to surface movements. The strong accelerations observed on some rock glaciers, however, induce a change of magnitude, and may threaten in some cases downslope areas. Thus, the presence of active or inactive rock glaciers with high ice content must be considered not only with regard to present conditions and dynamics, but with respect to possible evolutions due to climate change.

UAS-Based Change Detection of the Glacial and Proglacial Transition Zone at Pasterze Glacier, Austria

Glacier-related applications of unmanned aircraft systems (UAS) in high mountain regions with steep topography are relatively rare. This study makes a contribution to the lack of UAS applications in studying alpine glaciers in the European Alps. We transferred an established workflow of UAS-based change detection procedures to Austria’s largest glacier, the Pasterze Glacier. We focused on a selected part of the glacier tongue and its proglacial vicinity to obtain detailed knowledge of (i) the behavior of a lateral crevasse field, (ii) the evolution of glacier surface structures and velocity fields, (iii) glacier ablation behavior and the current glacier margin, and (iv) proglacial dead ice conditions and dead ice ablation. Based on two UAS flight campaigns, accomplished in 2016 (51 days apart), we produced digital elevation models (DEMs) and orthophotos with a ground sampling distance (GSD) of 0.15 m using Structure-from-Motion (SfM) photogrammetry. Electrical resistivity tomography (ERT) profiling was additionally conducted in the proglacial area. Results indicate distinct changes in the crevasse field with massive ice collapses, rapid glacier recession, surface lowering (mean of −0.9 m), and ice disintegration at the margins, calculated degree day factors on the order of −7 to −11 mm d−1·°C−1 for clean ice parts, and minimal changes of the debris-covered dead ice in the proglacial area. With this contribution we highlight the benefit of UAS in comparison to commonly used terrestrial methods and satellite-related approaches.

Glaciological Studies at Pasterze Glacier (Austria) Based on Aerial Photographs

This chapter describes and analyses glacier recession observed at Pasterze Glacier, Hohe Tauern Range, Austria, for the time period 2003–2009. Pasterze Glacier is the largest glacier of the entire Eastern Alps, and it is highly indicative of ongoing glacier melt in the Alps. We evaluated three glacier stages (2003, 2006 and 2009) and the glaciological changes between them. The quantitative analysis is based on aerial surveys carried out during the summer of these years. The photogrammetric workflow provided high resolution datasets, such as digital elevation models and orthophotos of each stage. We evaluated the extent, surface elevation, flow velocity field, supraglacial debris cover, and geomorphological changes at the glacier surface and the adjacent paraglacial environment. The main numerical results can be summarized as follows: the glacier covered 17.3 ± 0.1 km2 in 2009, the mean surface elevation change was −1.31 ± 0.07 m a−1 for the period 2003–2009, the glacier surface flow velocity in two test areas at the glacier tongue decelerated from 2003–2006 to 2006–2009 (−4 % and −31 %), and the debris cover of the glacier tongue increased from 63 % (2003) to 72 % (2009). We conclude that Pasterze Glacier is far from equilibrium and that its glacier tongue will turn into a large dead ice body in the near future.

Widespread occurrence of ephemeral funnel hoarfrost and related air ventilation in coarse‐grained sediments of a relict rock glacier in the seckauer tauern range, austria

Abstract This paper examines the occurrence of ephemeral hoarfrost crystals at funnel openings (funnel hoarfrost) detected between large blocks at the surface of the presumably relict chöneben ock lacier. Field mapping on 25 November 2011 identified 51 individual funnel openings with notable hoarfrost crystals distributed over the entire rock glacier. Hoarfrost was no longer detectable a few days after the initial mapping campaign. At least in the period 20–25 November 2011 temperature conditions at the rock glacier surface were favourable for hoarfrost formation and preservation as indicated by different types of measurements. A period of 24–48 h of hoarfrost‐suitable weather conditions would have been sufficient to form the observed hoarfrost if crystal growth rates of 2–4 mm h−1 are assumed. The void systems with funnel hoarfrost seem to be rather localised and limited in horizontal (10s of metres) and vertical (some metres) extent. Presumably the observed funnel hoarfrost was caused by the so‐called chimney effect, although no larger reversible air circulation systems with warm air exhalation were identified. Continuous ground temperature data from several sites at the rock glacier surface (period November 2011–December 2012) showed that hoarfrost sites are cooler and thermally buffered compared with non‐hoarfrost sites at similar elevations. This seems to be related to the decoupling of the air above the rock glacier and the pore air during periods of atmospheric warming. Only the combination of specific micro‐climatic (temperature/humidity), geometric (open void systems) and sedimentological (grain size/sediment structure) conditions allow the formation of the ephemeral funnel hoarfrost at this rock glacier.

Deglaciation and its impact on permafrost and rock glacier evolution: New insight from two adjacent cirques in Austria

Glaciers and permafrost are strongly linked to each other in mid-latitude mountain regions particularly with polythermal glaciers. This linkage is not only climatically defined but also in terms of geomorphic and glaciological processes. We studied two adjacent cirques located in the Central Austria. We focussed on the deglaciation since the Little Ice Age (LIA) maximum (c.1850CE) and its relevance for permafrost and rock glacier evolution since then. One cirque is occupied by a glacier remnant whereas the second one is occupied by an active rock glacier which was partly overridden by a glacier during the LIA. We applied a multidisciplinary approach using field-based techniques including geoelectrics, geodetic measurements, and automatic monitoring as well as historic maps and photographs, remote sensing, and digital terrain analysis. Results indicate almost complete deglaciation by the end of the last millennium. Small-scale tongue-shaped landforms of complex origin formed during the last decades at finer-grained slope deposits below the cirque headwalls. Field evidences and geophysics results proved the existence of widespread sedimentary ice beneath a thin veneer of debris at these slopes. The variable thickness of the debris layer has a major impact on differential ablation and landform evolution in both cirques. The comparison of digital elevation models revealed clear mass losses at both cirques with low rates between 1954 and 2002 and significantly higher rates since then. The central and lower part of the rock glacier moves fast transporting sediments and ice downvalley. In contrast, the upper part of the rock glacier is characterised by low debris and ice input rates. Both effects cause a significant decoupling of the main rock glacier body from its nourishment area leading eventually to rock glacier starvation. This study demonstrates the importance of a decadal-scale and multidisciplinary research approach in determining the development of alpine landforms over both space and time.