| 1. |
- Bonow, Johan M., et al.
(author)
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Cenozoic uplift of Nuussuaq and Disko, West Greenland : elevated erosion surfaces as uplift markers of a passive margin
- 2006
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 80:3-4, s. 325-337
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Journal article (peer-reviewed)abstract
- Remnants of a high plateau have been identified on Nuussuaq and Disko, central West Greenland. We interpret the plateau as an erosion surface (the summit erosion surface) formed mainly by a fluvial system and graded close to its former base level and subsequently uplifted to its present elevation. It extends over 150 km east–west, being of low relative relief, broken along faults, tilted westwards in the west and eastwards in the east, and having a maximum elevation of ca. 2 km in central Nuussuaq and Disko. The summit erosion surface cuts across Precambrian basement rocks and Paleocene–Eocene lavas, constraining its age to being substantially younger than the last rift event in the Nuussuaq Basin, which took place during the late Maastrichtian and Danian. The geological record shows that the Nuussuaq Basin was subjected to subsidence of several kilometres during Paleocene–Eocene volcanism and was transgressed by the sea later during the Eocene. By comparing with results from apatite fission track analysis and vitrinite reflectance maturity data, it is suggested that formation of the erosion surface was probably triggered by an uplift and erosion event starting between 40 and 30 Ma. Surface formation was completed prior to an uplift event that started between 11 and 10 Ma and caused valley incision. This generation of valleys graded to the new base level and formed a lower erosion surface, at most 1 km below the summit erosion surface, thus indicating the magnitude of its uplift. Formation of this generation of valleys was interrupted by a third uplift event also with a magnitude of 1 km that lifted the landscape to near its present position. Correlation with the fission-track record suggests that this uplift event started between 7 and 2 Ma. Uplift must have been caused initially by tectonism. Isostatic compensation due to erosion and loading and unloading of ice sheets has added to the magnitude of uplift but have not significantly altered the configuration of the surface. It is concluded that the elevations of palaeosurfaces (surfaces not in accordance with present climate or tectonic conditions) on West Greenland's passive margin can be used to define the magnitude and lateral variations of Neogene uplift events. The striking similarity between the landforms in West Greenland and those on many other passive margins is also noted.
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| 2. |
- Bonow, Johan M.
(author)
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Re-exposed basement landforms in the Disko region, West Greenland : disregarded data for estimation of glacial erosion and uplift modelling
- 2005
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 74:1-4, s. 106-127
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Journal article (peer-reviewed)abstract
- Classifications of large-scale landscapes in Greenland have traditionally been based on type and intensity of glacial erosion, with the general idea that present landforms are mainly the result of erosion from ice sheets and glaciers. However, on southern Disko and in areas offshore in Disko Bugt, a basement surface has preserved remnants of weathered gneiss and pre-Paleocene landforms, recently exhumed from Paleocene basalt. Isolated hills and lineaments have been mapped in a digital terrain model and aerial photographs. Offshore have hills been mapped from seismic lines. The medium size bedrock forms on southern Disko as tors, clefts and roche moutonées have been studied in the field. Remnant saprolites were inventoried, sampled and analysed according to grain size and clay mineralogy. The basement surface retains saprolites up to 8 m thick in close relation to the cover rocks. The landforms in the basement rocks belong essentially to an etched surface only slightly remodelled by glacial erosion and, below the highest coastline, also by wave action. The outline of hills is governed by two lineament directions, ENE–WSW representing the schistocity of the gneiss and NW–SE fracture zones. These structures are thus interpreted to have been exploited by the deep weathering while the frequent N–S lineaments have not and thus might be younger. Main ice-flow has been from the NE and has resulted in plucking of SW facing lee sides, however the resulting bedrock forms are mainly controlled by structures and orientation of joints. The identification of re-exposed sub-Paleocene etch forms on Disko and the hills of similar size offshore, forming a hilly relief, have implications for identification of a hilly relief south of Disko Bugt, its relation to younger planation surfaces as well as for conclusions of uplift events.
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| 3. |
- Ehsani, Amir Houshang, et al.
(author)
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Geomorphometric feature analysis using morphometric parameterization and artificial neural networks
- 2008
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 99:1-4, s. 1-12
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Journal article (peer-reviewed)abstract
- This paper presents a semi-automatic method using an unsupervised neural network to analyze geomorphometric features as landform elements. The Shuttle Radar Topography Mission (SRTM) provided detailed digital elevation models (DEMs) for all land masses between 60 degrees N and 57 degrees S. Exploiting these data for recognition and extraction of geomorphometric features is a challenging task. Results obtained with two methods, Wood's morphometric parameterization and the Self Organizing Map (SOM), are presented in this paper. Four morphometric parameters (slope, minimum curvature, maximum curvature and cross-sectional curvature) were derived by fitting a bivariate quadratic surface with a window size of 5 by 5 to the SRTM DEM. These parameters were then used as input to the two methods. Wood's morphometric parameterization provides point-based features (peak, pit and pass), line-based features (channel and ridge) and area-based features (planar). Since point-based features are defined as having a very small slope when their neighbors are considered, two tolerance values (slope tolerance and curvature tolerance) are introduced. Selection of suitable values for the tolerance parameters is crucial for obtaining useful results. The SOM as an unsupervised neural network algorithm is employed for the classification of the same morphometric parameters into ten classes characterized by morphometric position (crest, channel, ridge and plan area) subdivided by slope ranges. These terrain features are generic landform element and can be used to improve mapping and modeling of soils, vegetation, and land use, as well as ecological, hydrological and geomorphological features. These landform elements are the smallest homogeneous divisions of the land surface at the given resolution. The result showed that the SOM is an efficient scalable tool for analyzing geomorphometric features as meaningful landform elements, and uses the, full potential of morphometric characteristics.
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| 4. |
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| 5. |
- Gustavsson, Marcus, et al.
(author)
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A new symbol- and GIS-based detailed geomorphological mapping system: renewal of a scientific discipline for understanding landscape development
- 2006
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 77:1-2, s. 90-111
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Journal article (peer-reviewed)abstract
- This paper presents a comprehensive and flexible new geomorphological combination legend that expands the possibilities of current geomorphological mapping concepts. The new legend is presented here at scale of 1:10,000 and it combines symbols for hydrography, morphometry/morphography, lithology and structure with colour variations for process/genesis and geologic age. The piece-by-piece legend forms a “geomorphological alphabet” that offers a high diversity of geomorphological information and a possibility for numerous combinations of information. This results in a scientific map that is rich in data and which is more informative than most previous maps but is based on a simple legend. The system is developed to also be used as a basis for applications in GIS. The symbol-based information in the geomorphological maps can be digitally stored as a powerful database with thematic layers and attribute tables. By combining and further developing aspects of different classical mapping systems and techniques into expanded data combinations, new possibilities of presentation and storage are developed and thus a strong scientific tool is provided for landscape configuration and the reconstruction of its development; in turn the combination paves the way for specific thematic applications. The new system is illustrated for two contrasting landscape types: the first is located on the border of Vorarlberg, western Austria, and Liechtenstein in a glacially influenced, high altitude alpine setting that is strongly modified by various degradation processes; the second area represents a formerly glaciated region in Dalarna, central Sweden near Mora, an area that is characterized by a variety of aeolian, fluvial, glaciofluvial and lacustrine depositional and erosional landforms and also reflects isostatic uplift. The new method functions well for both areas and results in detailed scientific outlines of both landscape types.
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| 6. |
- Gustavsson, Marcus, et al.
(author)
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New geomorphological mapping system used at different scales in a Swedish glaciated area
- 2009
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 110:1-2, s. 37-44
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Journal article (peer-reviewed)abstract
- A new, detailed geomorphological mapping system is tested at different scales for presentation of landscape configuration and interpretation of landscape development of a formerly glaciated area near Mora in central Sweden. The geomorphological maps are based on fieldwork supported by aerial photographs. The area contains landforms created by mass movement, glacial, glaciofluvial, fluvial, lacustrine, aeolian and anthropogenic processes. In addition, geomorphological effects of isostatic uplift, which has caused a c. 220 m rise of the former Ancylus lake shoreline in the area since the deglaciation, can be seen. The new system is tested at scales 1:5000, 1:25,000 and 1:50,000 using the same legend. At the largest scale information on morphography/morphometry, lithology, and hydrography are included in the map as are details on polygenetic origins of landforms. With each step from the 1:5000 to the 1:50,000 scale some generalisation is needed at the cost of descriptive detail. In turn, with smaller scale, the general overview of the area increases and the impression from the map gradually becomes more dominated by genesis. The emphasis of the map thus changes from a presentation with a high level of descriptive information at the largest scale to a more interpretative overview at smaller scales. The scale transformation shows that the geomorphological presentation of the landscape is a function of both the landscape hierarchy and the geomorphological context within an area. The use of the new geomorphological mapping system at the three scales shows that the tested mapping legend can be used without modification from one scale to another. This is mainly because the geomorphological information parameters are separated in the legend, and that explanatory information is gained from combinations of them. The possibility to apply the same legend at different scales for an area facilitates the choice of an appropriate mapping scale for specific purposes and applications. The new mapping system also has the advantage that the data can be easily transformed into a GIS ESRI geodatabase containing the same "raw-data" as the original map. The differences of information at the different scales illustrate problems that are also relevant for use and presentation of geomorphological data in a GIS and three examples of scale problems in relation to GIS data handling are outlined.
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| 7. |
- Gustavsson, Marcus, et al.
(author)
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Structure and contents of a new geomorphological GIS database linked to a geomorphological map - with an example from Liden, central Sweden
- 2008
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 95:3-4, s. 335-349
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Journal article (peer-reviewed)abstract
- This paper presents the structure and contents of a standardised geomorphological GIS database that stores comprehensive scientific geomorphological data and constitutes the basis for processing and extracting spatial thematic data. The geodatabase contains spatial information on morphography/morphometry, hydrography, lithology, genesis, processes and age. A unique characteristic of the GIS geodatabase is that it is constructed in parallel with a new comprehensive geomorphological mapping system designed with GIS applications in mind. This close coupling enables easy digitalisation of the information from the geomorphological map into the GIS database for use in both scientific and practical applications. The selected platform, in which the geomorphological vector, raster and tabular data are stored, is the ESRI Personal geodatabase. Additional data such as an image of the original geomorphological map, DEMs or aerial orthographic images are also included in the database. The structure of the geomorphological database presented in this paper is exemplified for a study site around Liden, central Sweden.
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| 8. |
- Haussmann, Natalie, et al.
(author)
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Interactions between a cushion plant (Azorella selago) and surface sediment transport on sub-Antarctic Marion Island
- 2009
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 107:3-4, s. 139-148
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Journal article (peer-reviewed)abstract
- On sub-Antarctic Marion Island cushions of the dominant vascular plant species, Azorella selago, interact with the geomorphology of fellfield landscapes by affecting sediment distribution and ultimately terrace formation. Here, to understand the consequences of Azorella cushions for substrate movement and sorting, we quantified the size and shape of Azorella cushions and the grain size distribution of sediment surrounding these cushions, using a combination of image analysis approaches. Results show that as cushions become larger, they tend to become more elongated and grow more perpendicular to the slope. Mean and variance of grain size were greater upslope of Azorella cushions, while the number of particles was higher downslope of cushions, although these differences were not significant at all sites studied. Differences between upslope and downslope particle sizes were, however, not related to cushion elongation or growth angle as had been expected. The observed sediment partitioning is likely caused by a combination of frost-related sediment transport and Azorella cushions acting as sediment obstructions. Understanding these interactions between Azorella cushions and the landscape is especially important in the light of recent warming and drying on the island, as particle size affects soil properties such as water-holding capacity and frost susceptibility.
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| 9. |
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| 10. |
- Stroeven, Arjen, et al.
(author)
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Landscape analysis of the Huang He headwaters, NE Tibetan Plateau — Patterns of glacial and fluvial erosion
- 2009
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In: Geomorphology. - : Elsevier. - 0169-555X .- 1872-695X. ; 103:2, s. 212-226
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Journal article (peer-reviewed)abstract
- The large-scale geomorphology of the Huang He (Yellow River) headwaters, centered around the Bayan Har Shan (5267 m asl) in the northeastern part of the Tibetan Plateau, is dominated by an uplifted remnant of a low-relief relict plateau with several mountain ranges. We have performed geomorphological mapping using SRTM topographic data and Landsat 7 ETM+ satellite imagery to evaluate landscape characteristics and patterns, and to investigate the relative importance of different erosional processes in the dissection of this plateau remnant. The distribution of valley morphologies indicates that the eastern and southern margins of the plateau remnant have been extensively dissected by the Huang He and Chang Jiang (Yangtze) rivers and associated tributaries, while the mountain ranges have valley morphologies with U-shaped cross-sections that indicate large impacts from glacial erosion during Quaternary glaciations. An east-west decrease in the abundance of glacial valleys in mountains above 4800 m asl suggests that the diminishing size of the mountain blocks, coupled with increased continentality, resulted in more restricted glaciations to the west. Glacial valleys in mountain blocks on the plateau remnant are wider and deeper than adjacent fluvial valleys. This indicates that, integrated over time, the glacial system has been more effective in eroding the mountains of the relict upland surface than the fluvial system. This erosion relationship is reversed, however, on the plateau margin where dramatic fluvial rejuvenation in valleys that are part of the Huang He and Chang Jiang watersheds has consumed whatever glacial morphology existed. A remarkable correspondence exists between the outline of the relict plateau remnant and the outline that has been proposed for the Huang He Ice Sheet. This coincidence could mean that the Huang He Ice Sheet was larger than originally proposed, but that evidence for this has been consumed by fluvial incision at the plateau margin. Alternatively, this coincidence could indicate that what has been described as an ice sheet border is merely the outline of a relict plateau landscape. In apparent support of the latter, the absence of large-scale glacial geomorphological evidence on the plains of the relict plateau surface is not consistent with the hypothesis of a Huang He Ice Sheet.
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