Rock glacier dynamics in Southern Carpathian Mountains from high-resolution optical and multi-temporal SAR satellite imagery

Marius Necsoiu, Alexandru Onaca, Sarah Wigginton, Petru Urdea
<span title="">2016</span> <i title="Elsevier BV"> <a target="_blank" rel="noopener" href="" style="color: black;">Remote Sensing of Environment</a> </i> &nbsp;
The dynamics of rock glaciers in marginal periglacial environments are poorly 11 understood, especially in Eastern Europe where the enhanced continentality produces a distinct 12 pattern of periglacial phenomena. Multi-temporal image analysis of high-resolution optical and 13 radar satellite imagery of the Southern Carpathian Mountains, Romania revealed the small 14 dynamic nature and a slow geomorphologic evolution of rock glaciers over a 46-yr period of 15 record . Nine rock glaciers located
more &raquo; ... n glacial cirques and troughs within the central 16 area of Retezat Mountain were included in this study. Overall, the estimated displacement rates 17 are extremely low (i.e., a few cm/year) compared with other active rock glaciers from all over 18 the world. Despite their relative attenuated activity, it appears that Judele, Valea Rea, and 19 Pietrele are still active rock glaciers, but in an evident disequilibrium/imbalance with the actual 20 climate. These findings document the lowest altitude and easternmost active rock glaciers at this 21 Rock Glacier Dynamics in Southern Carpathian Mountains 1 latitude from Europe. Quantitative investigations were concentrated on Pietrele rock glacier, 22 subject of recent field campaigns. Optical data analysis indicated a slight acceleration of the 23 horizontal velocities at the surface of Pietrele rock glacier in recent years. This acceleration 24 appears to be caused by an increase in the temperature of permafrost, resulting from an evident 25 warming of external air temperature. Radar data analysis suggested seasonal variability of 26 surface motion, with higher deformation in autumn, whereas in early summer or spring the 27 deformation is negligible. Overall, the results obtained with cross-correlation analysis, 28 interferometric synthetic aperture radar (InSAR) coherence analysis, and Small BAseline Subset 29 (SBAS) multitemporal interferometry, are consistent, displaying similar deformation patterns 30 with the highest creep rates located in the southern and western portions of the glacier. These 31 findings are supported by thermal and geophysical measurements, which suggest the probable 32 presence of permafrost within these areas. The observed displacements were interpreted as 33 permafrost creep, and their very low velocity rates suggest the deforming frozen layers are very 34 thin. These results provide (i) baseline information and decadal-scale trends and a (ii) strategy 35 for future monitoring of the health and integrity of the rock glacier environment in the 36 Carpathian Mountains. 37 38 40 41 Rock Glacier Dynamics in Southern Carpathian Mountains 2 42 58 they represent a major portion of the high alpine mass transport system and form an integral part 59 of the landscape (Berthling and Etzelmüller, 2007; Azócar and Brenning, 2010). Rock glaciers 60 are sensitive to climate change, but not as sensitive as true glaciers, because the course debris 61 mantle produces a relative by large thermal inertia of permafrost (Haeberli et al 2006). 62 However, recent studies highlighted the increased sensitivity of permafrost when the temperature 63 of the subsurface is close to 0 °C (Kääb et al, 2007). Investigation of rock glacier dynamics 64 Rock Glacier Dynamics in Southern Carpathian Mountains 3 contributes to understanding the evolution of permafrost related formations in both space and 65 time, as well as under different climatic conditions (Frauenfelder and Kääb 2000; Frauenfelder et 66 al 2001). A recent estimate of the global permafrost area (i.e., permafrost area including 67 Antarctic and sub-sea permafrost) was estimated to be 16-21 × 10 6 km 2 , whereas the global 68 permafrost region (i.e., exposed land surface below which some permafrost can be expected) was 69 estimated to be 22 ± 3 × 10 6 km 2 (Gruber 2012). Monitoring rock glacier dynamics is, in most 70 cases, based on quantifying changes of three different components: horizontal velocities, vertical 71 velocities, and the front advance. Horizontal velocity measurements have shown that movement 72 rates are considerably slower (creep-like movement) than those of normal (ice) glaciers, ranging 73 from a few centimeters to a few meters per year (Haeberli 1985; Whalley and Martin 1992;; 74 Kääb and Vollmer 2000; Strozzi et al 2004; Lambiel and Delaloye 2004; Roer 2005; Delaloye et 75 al 2008; Serrano et al 2010; Liu et al 2013). Although most measured rock glacier velocities lay 76 within these limits, there are a few studies reporting unusually fast velocities of up to 100 m/yr, 77 reported by Corte (1987) in the Andes, Gorbunov et al (1992) in Asia, and Delaloye et al (2010) 78 in the Swiss Alps. 79 Globally, a large percentage of mountainous areas covered by rock glaciers either have not been 80 surveyed, or the existing ground information is too noisy to derive trends in ground movement. 81 This holds true for the Southern Carpathian Mountains, where field observations of rock glacier 82 dynamics are scarce and do not provide a complete view of rock glacier movement and other 83 processes. Because the permafrost exists in marginal conditions in the Southern Carpathians, 84 specifically in Retezat Mountains (Onaca et al 2013), it is important to determine if the 85 autochthonous rock glaciers show the same kind of interannual variations in flow velocity as 86 Rock Glacier Dynamics in Southern Carpathian Mountains 4 detected in the European Alps (Haeberli et al 2006) and elsewhere (e.g., Janke 2005; Liu et al 87 2013). 88 The overall objective of this study was to quantify subtle landscape changes that are diagnostic 89 of the health of near-surface permafrost of the mountainous environment of Retezat National 90 Park (RNP), Southern Carpathian Mountains, Romania. Specifically, the dynamics of rock 91 glaciers were assessed using complementary remote sensing techniques and satellite imagery 92 acquired over almost half a century. Because field data measurements were only recently 93 available, the study of the similarities and differences between results of the satellite-based 94 techniques and field observations was essential. 95 96
<span class="external-identifiers"> <a target="_blank" rel="external noopener noreferrer" href="">doi:10.1016/j.rse.2016.02.025</a> <a target="_blank" rel="external noopener" href="">fatcat:z4m3vyktbfbbhn2pg6uefjug6q</a> </span>
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