| 1. |
- Kienholz, Christian, et al.
(författare)
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A new semi-automatic approach for dividing glacier complexes into individual glaciers
- 2013
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 59:217, s. 925-937
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Tidskriftsartikel (refereegranskat)abstract
- Many glaciological and hydrological studies require outlines of individual glaciers rather than total ice cover. Here we develop a new semi-automatic algorithm that uses a digital elevation model (DEM) and outlines of glacier complexes to calculate the extents of individual glaciers. The algorithm first applies hydrological modeling tools to a modified DEM to calculate flowsheds. It then merges flowsheds that belong to individual glaciers using a distance-based approach, whose required empirical parameters are derived from the Juneau Icefield area in Alaska. In this region, 2% of similar to 1300 glaciers were misclassified. The algorithm was validated on >25 000 km(2) of ice in other regions in Alaska and on >40 000 km(2) of ice in Arctic Canada, resulting in similar to 2% and similar to 3% misclassified glaciers, respectively. Results indicate that the algorithm is robust provided the DEM and the outlines are of good quality.
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| 2. |
- Kienholz, Christian, et al.
(författare)
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Derivation and analysis of a complete modern-date glacier inventory for Alaska and northwest Canada
- 2015
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 61:227, s. 403-420
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed, complete glacier inventory for Alaska and neighboring Canada using multi-sensor satellite data from 2000 to 2011. For each glacier, we derive outlines and 51 variables, including center-line lengths, outline types and debris cover. We find 86 723 km(2) of glacier area (27 109 glaciers >0.025 km(2)), similar to 12% of the global glacierized area outside ice sheets. Of this area 12.0% is drained by 39 marine-terminating glaciers (74 km of tidewater margin), and 19.3% by 148 lake- and river-terminating glaciers (420 km of lake-/river margin). The overall debris cover is 11%, with considerable differences among regions, ranging from 1.4% in the Kenai Mountains to 28% in the Central Alaska Range. Comparison of outlines from different sources on >2500 km(2) of glacierized area yields a total area difference of similar to 10%, emphasizing the difficulties in accurately delineating debris-covered glaciers. Assuming fully correlated (systematic) errors, uncertainties in area reach 6% for all Alaska glaciers, but further analysis is needed to explore adequate error correlation scales. Preliminary analysis of the glacier database yields a new set of well-constrained area/length scaling parameters and shows good agreement between our area altitude distributions and previously established synthetic hypsometries. The new glacier database will be valuable to further explore relations between glacier variables and glacier behavior.
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| 3. |
- Kienholz, Christian, et al.
(författare)
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Mass Balance Evolution of Black Rapids Glacier, Alaska, 1980-2100, and Its Implications for Surge Recurrence
- 2017
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Surge-type Black Rapids Glacier, Alaska, has undergone strong retreat since it last surged in 1936-1937. To assess its evolution during the late Twentieth and Twenty-first centuries and determine potential implications for surge likelihood, we run a simplified glacier model over the periods 1980-2015 (hindcasting) and 2015-2100 (forecasting). The model is forced by daily temperature and precipitation fields, with downscaled reanalysis data used for the hindcasting. A constant climate scenario and an RCP 8.5 scenario based on the GFDL-CM3 climate model are employed for the forecasting. Debris evolution is accounted for by a debris layer time series derived from satellite imagery (hindcasting) and a parametrized debris evolution model (forecasting). A retreat model accounts for the evolution of the glacier geometry. Model calibration, validation and parametrization rely on an extensive set of in situ and remotely sensed observations. To explore uncertainties in our projections, we run the glacier model in a Monte Carlo fashion, varying key model parameters and input data within plausible ranges. Our results for the hindcasting period indicate a negative mass balance trend, caused by atmospheric warming in the summer, precipitation decrease in the winter and surface elevation lowering (climate-elevation feedback), which exceed the moderating effects from increasing debris cover and glacier retreat. Without the 2002 rockslide deposits on Black Rapids' lower reaches, the mass balances would be more negative, by similar to 20% between the 2003 and 2015 mass-balance years. Despite its retreat, Black Rapids Glacier is substantially out of balance with the current climate. By 2100, similar to 8% of Black Rapids' 1980 area are projected to vanish under the constant climate scenario and similar to 73% under the RCP 8.5 scenario. For both scenarios, the remaining glacier portions are out of balance, suggesting continued retreat after 2100. Due to mass starvation, a surge in the Twenty-first century is unlikely. The projected retreat will affect the glacier's runoff and change the landscape in the Black Rapids area markedly.
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| 4. |
- Pfeffer, W. Tad, et al.
(författare)
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The Randolph Glacier Inventory : a globally complete inventory of glaciers
- 2014
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 60:221, s. 537-552
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Tidskriftsartikel (refereegranskat)abstract
- The Randolph Glacier Inventory (RGI) is a globally complete collection of digital outlines of glaciers, excluding the ice sheets, developed to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change for estimates of past and future mass balance. The RGI was created with limited resources in a short period. Priority was given to completeness of coverage, but a limited, uniform set of attributes is attached to each of the similar to 198 000 glaciers in its latest version, 3.2. Satellite imagery from 1999-2010 provided most of the outlines. Their total extent is estimated as 726 800 +/- 34 000 km(2). The uncertainty, about +/- 5%, is derived from careful single-glacier and basin-scale uncertainty estimates and comparisons with inventories that were not sources for the RGI. The main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover. These errors appear not to be normally distributed, and quantifying them reliably is an unsolved problem. Combined with digital elevation models, the RGI glacier outlines yield hypsometries that can be combined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers. The RGI has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume, and thus actual and potential contributions to sea-level rise.
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| 5. |
- Wastlhuber, Roland, et al.
(författare)
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Glacier Changes in the Susitna Basin, Alaska, USA, (1951-2015) using GIS and Remote Sensing Methods
- 2017
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- The Susitna River draining from the highly glacierized Central Alaska Range has repeatedly been considered a potential hydro-power source in recent decades, raising questions about the effect of glacier changes on the basin's river runoff. We determine changes in the glacier area (1951-2010), elevation (1951-2010, 1951-2005 and 2005-2010), equilibrium line altitude (ELA, 1999-2015), and accumulation area ratio (AAR, 1999-2015) of the basin's five largest glaciers covering 587 km(2) (2010). We use the Landsat time series, as well as digital elevation models (DEMs) from 1951 (United States Geological Survey (USGS) aerial imagery), 2005 (Advanced Spaceborne Thermal Emission and Reflection Radiometer, ASTER), and 2010 (airborne interferometric synthetic aperture radar, IfSAR). The glaciers lost an area of 128 +/- 15 km(2) (16%) between 1951 and 2010. The mean ELA was located at 1745 +/- 88 m a.s.l. during 1999-2015. The glacier's annual ELAs do not show any significant trends. We found a glacier-wide elevation change of 0.41 +/- 0.07 m yr(-1) for the period 1951-2005 and -1.20 +/- 0.25 m yr(-1) for 2005-2010. The results indicate that the glaciers are in a state of retreat and thinning, and have been losing mass at an accelerated rate in recent years. The interpretation of the thickness changes is complicated by the glaciers' surge cycles.
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