The understanding of permafrost distribution in Iceland is still limited and current knowledge is mainly based on small scale observations and regional modelling using temperature data. In the Alps Perennial Snow Patches have been considered to protect permafrost from solar radiation and are used as an indicator for the occurrence of local permafrost. In this study perennial snow fields are detected and classified based on aerial and satellite images. Effects of climatic and topographic factors on the snow field occurrence are investigated aiming to provide insight into the distribution of local permafrost in northern Iceland. Multi-temporal optical satellite images (Landsat-5/-7/-8 and Sentinel-2, 1984–2017) have revealed a time-variable distribution of perennial snow patches as possible permafrost indicators on the Tröllaskagi Peninsula in northern Iceland. Calculated normalized difference snow index in combination with different threshold values at the end of summer season within six selected study areas show that several snow patches are present in a time period of over 30 years. Perennial snow patches in the study areas exhibit strong fluctuations in extent due to different local characteristics, e.g. elevation, aspect or topography (plateau/open slopes vs. valleys/cirques). In three of the six study areas snow patches have a high probability of occurrence and the pattern of the distribution is very similar in each time period. Comparison with climate data from nearby weather stations indicates that perennial snow patches can be used in combination with mean annual air temperatures as indicators for local permafrost distributions.
Rockfalls are a major aspect concerning morphodynamics in high mountain areas and represent a serious hazard for people and infrastructure. Recently, an increase of rockfall activity has been observed which is probably related to the destabilization of rock slopes through climate-related changes of the mountain cryosphere. This study investigates the rockfall distribution during a 4-year monitoring period by systematic observation with bitemporal Airborne Laser Scanning DTMs in an area of 610.7 km² in the Ötztal Alps/Tyrol, Austria. The analyses of the 93 detected rockfall events indicate that rockfall activity is highest in proglacial areas. Further 83.9% of all rockfall source areas were mapped in bedrock where the modelled mean annual ground temperature (MAGT) indicates perennial frozen conditions. The results demonstrate the importance of thermal effects on the destabilization of rock faces and show that the triggering of rockfalls is closely related to changes in the glacier and permafrost regime. 18 low-magnitude rockfalls with volumes between 69 ± 3 m³ and 8420 ± 89 m³ are examined in detail. On the base of the analysis of these events energy line angles of 28.7°for the Fahrböschung and 19.9°for the minimum shadow angle can be derived and significantly longer runout distances on glaciated rockfall paths are observed.
<p>Climate change has serious implications for the cryosphere and a close relationship between the instability of rock faces and the changes in high mountain permafrost is suspected. Although, the number of rockfall events in Alpine areas is increasing, detailed analyses of the frequency and runout distances in high altitudes are rare. This study gives an insight into the rockfall activity in the &#214;tztal Alps in Tyrol, Austria. A systematic observation utilizing bi-temporal ALS-DTMs in combination with orthoimages revealed a total of 93 rockfalls over an area of 637 km&#178; in the period from 2006 to 2010. Since more than 90&#160;% of the rockfall release areas were mapped in potential permafrost areas, a correlation between rockfall activity and climatically driven degradation of permafrost in bedrock is very likely. 18 rockfall events, ranging in volume from 69 to 8420 m&#179;, were suitable for runout assessments. To estimate the maximum range of future rockfalls with empirical models, values of 30&#160;&#176; (Fahrb&#246;schung) and 26&#160;&#176; (minimum shadow angle) can be proposed for risk assessment at a regional scale (1:25,000 &#8211; 1:100,000). Rockfalls occurring on snow or ice may also go below these values.</p><p><strong>Keywords</strong>: Rockfall, Permafrost, digital elevation model; runout distance, Fahrb&#246;schung, minimum shadow angle, &#214;tztal Alps</p>
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