C13B-01 INVITED
Quantification of Permafrost Creep by Remote Sensing
Rockglaciers and frozen talus slopes are distinct landforms representing the occurrence of permafrost conditions in high mountain environments. The interpretation of ongoing permafrost creep and its reaction times is still limited due to the complex setting of interrelating processes within the system. Therefore, a detailed monitoring of rockglaciers and frozen talus slopes seems advisable to better understand the system as well as to assess possible consequences like rockfall hazards or debris-flow starting zones. In this context, remote sensing techniques are increasingly important. High accuracy techniques and data with high spatial and temporal resolution are required for the quantification of rockglacier movement. Digital Terrain Models (DTMs) derived from optical stereo, synthetic aperture radar (SAR) or laser scanning data are the most important data sets for the quantification of permafrost-related mass movements. Correlation image analysis of multitemporal orthophotos allow for the quantification of horizontal displacements, while vertical changes in landform geometry are computed by DTM comparisons. In the European Alps the movement of rockglaciers is monitored over a period of several decades by the combined application of remote sensing and geodetic methods. The resulting kinematics (horizontal and vertical displacements) as well as spatio-temporal variations thereof are considered in terms of rheology. The distinct changes in process rates or landform failures - probably related to permafrost degradation - are analysed in combination with data on surface and subsurface temperatures and internal structures (e.g., ice content, unfrozen water content).
C13B-02
InSAR Measurements of Ground Surface Deformation due to Thaw Settlement and Frost Heave Over Permafrost on the North Slope of Alaska
Permafrost in northern high-latitude regions plays significant roles in land surface energy, carbon exchange, and hydrological cycles. The freezing and thawing of the active layer over permafrost can cause significant ground displacements: uplift when the ground freezes, and subsidence when it thaws. Thickening of the active layer and melting of ground ice near the permafrost table may cause steady ground subsidence over years. Permafrost on the North Slope of Alaska experienced significant changes in the past several decades, such as increase in permafrost temperature and active layer thickness, development of thermokarst, and rapid erosion of coastal lines. Ground-based measurements indicate that ground displacement rates can be up to several centimeters per year. However, these measurements are site specific with very limited spatial coverage. In this study, we apply InSAR (Interferometric Synthetic Aperture Radar) processing to ERS-1/2 SAR data acquired during summer seasons to monitor inter-annual surface deformation in the area near Prudhoe Bay. We stack 17 interferograms spanning from 1992 to 2000 and estimate the secular deformation rates. We find that along four rivers (the Kuparuk, Sagavanirktok, Kadleroshilik, and Shaviovik Rivers, from west to east), the land areas were subsiding relative to the riverbeds at rates of 2-3 mm/yr. In the mean time, the Prudhoe Bay area was undergoing substantial relative uplift of 4-7 mm/yr. Deformation signals with spatial scales of a few hundred meters are also observed within the bay area. These relative ground motions are likely associated both with the complex permafrost behaviors and with oil fields activities. Detailed explanations of InSAR observations will be given.
C13B-03 INVITED
Determining Rates of Permafrost Degradation Using a Time-Series of High-Resolution Imagery
Quantifying the nature, extent, and rate of permafrost degradation requires high-resolution imagery because of the high variability in spatial and spectral characteristics of thermokarst landforms. Because rates of lateral degradation usually are <1 m/yr, a spatial resolution <2 m is required to adequately quantify degradation over 10–50 years. Due to the need for high-resolution imagery, however, it is practical to sample degradation only within small areas. We prefer to use high-resolution scans of film for historical airphotos, and to use newly acquired airphotos or high-resolution satellite imagery (e.g. Quickbird, Ikonos). Terrain-corrected satellite imagery is preferred as the base for georectifying and overlaying the historical photography. We prefer manual photointerpretation of permafrost boundaries over image processing because of the complexity of vegetation/surface water responses, and thus spectral characteristics, at the degrading margins. Change can be detected either by vectorizing boundaries of thermokarst landforms or point sampling across the entire time-series of images. While rates of surface permafrost degradation have yet to be assessed comprehensively in Alaska, our measurements of degradation at four sites across a climatic gradient using georectified airphotos provides some initial assessment. At Naknek in southwestern Alaska, the total area with recent thermokarst landforms developing in glacio-lacustrine deposits has increased from 35.5% in 1951 to 42% in 2000. On the Tanana Flats, central Alaska, recent thermokarst fens and bogs on abandoned floodplain deposits have increased from 39% in 1949 to 47% in 1995. At Cape Espenberg, Seward Peninsula, thermokarst lakes, basins, and thermokarst pits and troughs on eolian silt have increased from 73.9% in 1950 to 78.1% in 2005, with the high percentage of thermokarst terrain due to old, drained thaw-lake basins. At Fish Creek on the Beaufort Coastal Plain, where recent thermokarst polygonal troughs are common on flat upland terrain, and old drained-lake basins are common on sandy soils in lowland terrain, thermokarst showed little change between 1945 and 1982 (9%), but had expanded to 12.5% in 2001, due to thawing of ice wedges. Across all sites, thermokarst terrain increased in absolute percent area by 3.5 to 8% over the 47–55 year period, or a rates of 0.06–0.17% area/yr. Naknek and Fish Creek had more rapid thermokarst from ~1980 to ~2000, compared to the earlier ~1950 to ~1980 period, while Tanana Flats and Cape Espenberg showed constant rates of increase between the periods. At these relatively low rates, it will take 100s of years to completely degrade surface permafrost across an entire landscape, even with climate warming, due to the high latent heat contents of ice-rich soils and the ability of ecosystems to stabilize permafrost.
C13B-04 INVITED
Contemporary (1951-2001) Evolution of Lakes in the Old Crow Basin, Northern Yukon, Canada: Remote Sensing, Numerical Modeling, and Stable Isotope Analysis
This study reports on changes in the distribution, surface area and modern water balance of lakes and ponds located in the Old Crow Basin, northern Yukon, over a 50-year period (1951-2001) using aerial photographs, satellite imagery, a numerical lake model, and stable O-H isotope analysis. Results from the analysis of historical air photos (1951 and 1972) and a Landsat-7 Enhanced Thematic Mapper (ETM+) image (2001) show an overall decrease (-3.5%) in lake surface area between 1951 and 2001. Large lakes typically decreased in extent whereas ponds generally increased over the study period. This is corroborated by a numerical lake water balance simulation (P-E index) and stable O-H isotope analysis, which indicates that most lakes experienced a water deficit over the period 1988-2001. These observed trends in lake surface area are mainly attributable to a warmer and drier climate. The modern decrease in lake levels corresponds well to changes in regional atmospheric teleconnection patterns (Arctic and Pacific Decadal oscillations). In 1977, the climate in the region switched from a predominantly cool and moist regime, associated with the increase in lake surface area, to a hot and dry one, thus resulting in the observed decrease in lake surface area. Although some lakes may have drained catastrophically by stream erosion or bank overflow, it is not possible to determine with certainty which lakes experienced such catastrophic drainage since the air photos and the satellite image were acquired at about a 20-year interval.
C13B-05
Spatial dynamics of thermokarst and thermo-erosion at lakes and ponds in North Siberia and Northwest Alaska using high-resolution remote sensing
Formation, growth, and drainage of thermokarst lakes in ice-rich permafrost deposits are important factors of landscape dynamics in extent Arctic lowlands. Monitoring of spatial and temporal dynamics of such lakes will allow an assessment of permafrost stability and enhance the capabilities for modelling and quantifying biogeochemical processes related to permafrost degradation in a warming Arctic. In this study we use high-resolution remote sensing and GIS to analyze the development of thermokarst lakes and ponds in two study regions in North Siberia and Northwest Alaska. The sites are 1) the Cherskii region in the Kolyma lowland (Siberia) and 2) the Kitluk River area on the northern Seward Peninsula (Alaska). Both regions are characterized by continuous permafrost, a highly dissected and dynamic thermokarst landscape, uplands of Late Pleistocene permafrost deposits with high excess ice contents, and a large total volume of permafrost-stored carbon. These ice-rich Yedoma or Yedoma-like deposits are highly vulnerable to permafrost degradation forced by climate warming or other surface disturbance. Time series of high- resolution imagery (aerial, Corona, Ikonos, Alos Prism) covering more than 50 years of lake dynamics allow detailed assessments of processes and spatial patterns of thermokarst lake expansion and drainage in continuous permafrost. Time series of high-resolution imagery (aerial, Corona, Ikonos, Alos Prism) covering more than 50 years of lake dynamics allow detailed assessments of processes and spatial patterns of thermokarst lake expansion and drainage in continuous permafrost. Processes identified include thaw slumping, wave undercutting of frozen sediments or peat blocks and subsequent mass wasting, thaw collapse of near-shore zones, sinkhole formation and ice-wedge tunnelling, and gully formation by thermo-erosion. We use GIS-based tools to relate the remote sensing results to field data (ground ice content, topography, lithology, and relative age of landscape units). Results exhibit a very dynamic lake environment at both sites strongly related to landscape history and past cryolithological development. Lake shore erosion rates reach values of more than 1 m per year over the 50 year observation period at some sites. Permafrost degradation processes are identified as a key driver of both lake expansion and drainage.
C13B-06 INVITED
Remote sensing of erosion along ice-rich permafrost bluffs, Beaufort Sea coast, Alaska
Rates of shoreline erosion along Arctic coastlines have traditionally been among the highest in the world. However, recent studies of erosion along the Beaufort Sea coast in Alaska have found that rates are increasing relative to these historically high rates. Using a combination of high-resolution historic and contemporary aerial photography and satellite imagery we have also found an interesting shift in the pattern of erosion along a 60km segment of north facing coastline within the National Petroleum Reserve Alaska. Roughly 30 percent of the study coastline is subject to thermo-mechanical erosional niche formation and block collapse. Mean annual erosion rates for coastline types subject to this type of erosion have increased from 8 m/yr (1955-1979) to nearly 18 m/yr (2002-2007). Ice-poor permafrost bluffs had historically eroded at nearly twice the rate of ice-rich permafrost bluffs, however between 2002 and 2007 these bluff types eroded at nearly identical rates. Further, during the remainder of the 2007 ice-free season nearly 25 m of erosion occurred locally along ice-rich permafrost bluffs. The size of blocks that had collapsed during this time ranged from 6 to 12 m wide. This suggests that some areas potentially experienced 2 to 4 episodes of niche formation, block collapse, and block degradation within a single year. This process of erosion is believed to occur during westerly or northwesterly wind events that elevate sea level, removing slumped materials from the bluff toe, and attacking the base of the bluff creating the niche that leads to block collapse. However, during the 2007 ice-free season, an effective wind event of this sort did not occur.
C13B-07
Coastal Erosion History Retrieval using Multi-Sensor Imagery on the Permafrost Coasts of the Bykovsky Peninsula
This study investigates the pace of erosion during the 1951-2006 period on the Bykovsky Peninsula, located northeast of the harbour-town of Tiksi. The rates of erosion were retrieved using a wide array of imagery, ranging from airphotos to recent high resolution satellite imagery. The coastline, which is characterized by the presence of ice-rich sediment (ice complex) and the vicinity of the Lena River Delta, retreated at a mean rate of 0.59 m/yr between 1951 and 2006. Shoreline movement ranged from –434 m to +92 m (negative changes are erosional) and exhibited large variability (σ=45.4). 97.0% of the rates observed were less than 2 m/yr and 81.6% were less than 1 m/yr. No significant trend in erosion could be recorded despite the study of five temporal subperiods within 1951-2006. Erosion actually appears to be strongly dependant on the nature of the backshore material, being stronger along coastal stretches affected by past of current thermokarst activity. The juxtaposition of wind records for the town of Tiksi and erosion records yielded no significant relationship despite strong record amplitude for both datasets. We explain this poor relationship by the rough incorporation of sea ice cover in our storm extraction algorithm, the use of land-based wind records vs. offshore winds, the proximity of the Peninsula to the Lena River Delta freshwater plume, and the local topographical constraints on swell development. We put the results into a broader context by comparing those with other rates of erosion along Arctic coasts
C13B-08
Permafrost and Active Layer Modeling in the Northern Hemisphere using AVHRR Long- Term Records
High latitude environments such as those over northern Eurasia and North America are particularly vulnerable to climate change which is expected to be pronounced in these areas. Climate warming is likely to cause a permafrost thawing with subsequent effects on surface albedo, soil organic matter degradation, hydrology and greenhouse gas emissions. Recently, there have been a number of experiments to simulate soil temperature and permafrost dynamics on regional and global scales. In these simulations that employ some stand-alone equilibrium or transient permafrost models, the upper boundary conditions are usually the air temperature from observations or climate forcing from available Global or Regional Climate Models. In this research we used the GIPL-1.1 model, which is a spatially distributed model of permafrost based on an approximate analytical solution of soil freezing and thawing, which includes an estimation of thermal offset due to the difference in frozen and thawed soil thermal properties. The GIPL-1.1 model also accounts effectively for the effects of snow cover, vegetation, soil moisture, and soil thermal properties. Two decades of satellite clear sky thermal infrared data from 1981 to 2000 was used as an upper boundary conditions in order to simulate the distribution and temperatures of permafrost and active layer thickness in the entire Arctic and sub-Arctic permafrost domain. Under cloud-free conditions, infrared data provide skin depth (surface) temperatures and are shown to be generally consistent with surface air temperatures. The key source of historical surface temperature data is the Advanced Very High Resolution Radiometer (AVHRR) onboard National Oceanic and Atmospheric Administration satellites (Comiso, 2000, 2001, 2003). The results of permafrost modeling using GIPL-1.1 model show a very good agreement between calculated distribution of permafrost temperatures, observed data, and the distribution of permafrost derived from the International Permafrost Association (IPA) permafrost map.