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| 2. |
- Sahlin, Eva A. U., et al.
(author)
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Connectivity analyses of valley patterns indicate preservation of a preglacial fluvial valley system in the Dyfi basin, Wales
- 2009
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In: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 120, s. 245-255
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Research review (peer-reviewed)abstract
- Coastal valleys in the west part of Mid-Wales, such as the Mawddach, Dysynni, Tal-y-Ilyn and Dyfi, acted as corridors for ice which drained the Welsh Ice Cap during the Devensian. Analyses of detailed digital elevation models, and interpretation of satellite images and aerial photographs, show the existence of large variations in the amount of glacial modification between these valleys. Although all the valleys are glacially over-deepened along late Caledonian fault lines, only the Dyfi basin exhibits a dendritic pattern, with V-shaped cross-profiles and valley spurs typical of valleys formed by fluvial processes. Connectivity analysis of the Dyfi basin shows that it exhibits an almost completely dendritic pattern with connectivity alpha and beta values of 0.74 and 1.01, respectively, with little glacial modification of the preglacial fluvial valley pattern in the form of glacial valley breaching. Several examples of glacial meltwater incision into a well-developed pre-existing river valley system, causing river capture across watersheds, have been identified in the Dyfi basin. The degree of preservation of the preglacial fluvial valley system within the Dyfi basin indicates limited modification by glacial processes, despite the area being subjected to glacier activity during the Late Devensian at least. It is possible that major parts of the basin were covered by cold-based or slow-moving ice, close to, or under, a migrating ice-divide, with the major ice drainage Occurring along the weaker zone of the Pennal Fault along which teh Dyfi valley is located, causing minor adjustments to the Surrounding interfluves and uplands. it is proposed here that the general river valley morphology of the Dyfi basin is of a pre-Late Devensian age.
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| 3. |
- Sahlin, Eva A.U. 1971-, et al.
(author)
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Connectivity analyses of valley patterns reveal Devensian glacial drainage activity in Mid-Wales (poster)
- 2009
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Conference paper (other academic/artistic)abstract
- Coastal valleys in the west part of Mid-Wales, such as the Mawddach, Dysynni, Tal-y-llyn and Dyfi, are believed to have acted as corridors for ice which drained the Welsh Ice Cap during the Devensian. Connectivity analyses of valley patterns from detailed digital elevation models, and interpretation of satellite images and aerial photographs show the existence of large variations in the amount of glacial modification between these valleys. Although all the valleys are glacially over-deepened along Silurian fault lines, only the Dyfi basin exhibits a dendritic pattern, with V-shaped cross profiles and valley spurs typical of valleys formed by fluvial processes.The connectivity analyses show that the Dyfi basin exhibits a purely dendritic pattern with little glacial modification of the preglacial fluvial valley pattern in form of valley breaching. It is proposed here that the general river valley morphology of the Dyfi basin is of a pre-Late Devensian age. This suggests a complex glacial drainage history, where cold-based ice was not only confined to the interior uplands, but also covered low-altitude areas previously believed to be a major drainage conduit for the Welsh Ice Cap. This indicates that Late Devensian glacial erosion was not as intense as previously believed and larger areas might have been overlain by cold-based ice.
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| 4. |
- Sahlin, Eva A.U. 1971-, et al.
(author)
-
Evidence for cold-based ice at low altitudes : Preservation of a preglacial fluvial valley system in the Dyfi basin, Wales (poster)
- 2009
-
Conference paper (other academic/artistic)abstract
- Coastal valleys in the west part of mid-Wales, such as the Mawddach, Dysynni, Tal-y-llyn and Dyfi, are believed to have acted as corridors for ice which drained the Welsh Ice Cap during the Devensian. Analysis of detailed digital elevation models and interpretation of satellite images and aerial photographs show the existence of large variations in the amount of glacial modification between these valleys. Although all the valleys are glacially over-deepened along Silurian fault lines, only the Dyfi basin exhibits a dendritic pattern, with V-shaped cross profiles and valley spurs typical of valleys formed by fluvial processes. Connectivity analysis of the Dyfi basin shows that it exhibits a nearly dendritic pattern with connectivity α and β values of 0.74 and 1.01 respectively, with little glacial modification of the preglacial fluvial valley pattern in the form of valley breaching. It is proposed that the general river valley morphology of the Dyfi basin is of a pre-Late Devensian age. Several examples have been identified of glacial meltwater incision into a well-developed pre-existing river valley system, causing river capture across watersheds. The degree of preservation of the pre-glacial fluvial valley system within the Dyfi basin indicates limited modification by glacial processes, despite the area being subjected to Late Devensian glacier activity. It is possible that major parts of the basin were covered by cold-based or slow-moving ice close to or under a migrating ice divide, with the major ice drainage occurring along the weaker zone of the Pennal Fault, causing minor adjustments to the surrounding interfluves and uplands.
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