Editing Quaternary geology and geomorphology of the area around Kisdon, upper Swaledale - an excursion

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== Geological and geomorphological background ==
 
== Geological and geomorphological background ==
  
Bedrock in the area is upper Dinantian limestones, sandstones and shales ('Yoredale Series') with lower Namurian sandstones (Millstone Grit) capping the highest interfluves. A sandy '''diamicton''' with blocks of sandstone and shale (probably '''till''', but free of far-travelled '''erratics''') and blanket peat covers much of the fells. The steeper valley sides are relatively free of superficial deposits, although locally there are patches of till and landslide sediments. Most of the valley bottoms contain thick deposits of glacial and debris-flow diamictons, '''glaciofluvial''' sand and gravel and coarse-grained river gravels, although in the upper part of Skeb Skeugh fine-grained lake peats, '''gyttja''' and '''marls''' fill the valley bottom. In some places the valley bottoms are undergoing active incision and waterfalls reflect the differences in rock hardness.
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Bedrock in the area is upper Dinantian limestones, sandstones and shales ('Yoredale Series') with lower Namurian sandstones (Millstone Grit) capping the highest interfluves. A sandy '''diamicton''' with blocks of sandstone and shale (probably '''till''', but free of far-travelled '''erratics''') and blanket peat covers much of the fells. The steeper valley sides are relatively free of superficial deposits, although locally there are patches of till and landslide sediments. Most of the valley bottoms contain thick deposits of glacial and debris-flow diamictons, '''glaciofluvial''' sand and gravel and coarse-grained river gravels, although in the upper part of Skeb Skeugh fine-grained lake petits, '''gyttja''' and '''marls''' fill the valley bottom. In some places the valley bottoms are undergoing active incision and waterfalls reflect the differences in rock hardness.
  
The large-scale landforms of the area are visually impressive and geomorphologically intriguing. The Swale valley crosses the region from northwest to southeast, but takes a sharp right-angle bend at Hartlakes. However a valley of a similar size to the Swale, but with a tiny stream called Skeb Skeugh, extends south of Keld towards Thwaite, then bends sharply towards the east to rejoin the valley of the Swale just beyond Muker. Between these valleys, Kisdon forms an isolated hill some 200 m above the valley bottoms. The origin of Kisdon hill, the changing direction of the Swale valley and the virtually dry valley of Skeb Skeugh have long been a topic of debate.
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The large-scale landforms of the area are visually impressive and geomorphologically intriguing. The Swale valley crosses the region from northwest to southeast, but takes a sharp right-angle bend at Hartlakes. However a valley of a similar size to the Swale, but with a tiny stream called Skeb Skeugh, extends south of Keld towards Thwaite, then bends sharply towards the east to rejoin the valley of the Swale just beyond Muker. Between these valleys, Kisdon forms an isolated hill some 200 m above the valley bottoms. The origin of Kisdon hill, the changing direction of the Swale valley and the virtually dry valley of Skeb Skeugh have long been a topic of debate.
  
Many of the small-scale landforms are classical for their type and provide detailed evidence of the direction of ice movement across the region, the pattern of ice wastage, the response of rivers and oversteepened slopes to changes of climate over the past c. 15 000 years and the effects of human activity on river processes. Glaciofluvial landforms include a variety of glacial '''meltwater channels''' southwest of Keld, '''kames''' and '''kettle holes''' around Angram and Thwaite and '''kame terraces''' west of Muker. Evidence for climatically driven changes of river activity include a debris flow fan at Hartlakes, and river terraces along the Swale upstream of West Stonesdale Beck. Landforms produced by slope failure include a deep rotational slip at Hooker Mill, a massive debris slide on the northwest side of Kisdon, a massive debris flow at Usha Gap and a block glide at Birk Hill. In the upper part of Skeb Skeugh fine-grained lake sediments below the valley bottom preserve the record of Devensian Lateglacial and Holocene vegetational change, soil development and slope stability. In addition, river landforms show the effects of rock control, of human activity in determining sediment loads, and intrinsic within-channel processes resulting in the formation of large-scale boulder bedforms. The river terraces upstream of Kisdon Force have an extent and elevation determined by rock hardness. Those around Thwaite show the effects of reduced discharge of the present rivers relative to the discharges of the rivers that formed the main valley bottom floodplain slopes, while the impressive array of valley bottom terraces south of Hartlakes are the product of within-channel processes enhanced by sediment yield from the local lead mines.
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Many of the small-scale landforms are classical for their type and provide detailed evidence of the direction of ice movement across the region, the pattern of ice wastage, the response of rivers and oversteepened slopes to changes of climate over the past c. 15 000 years and the effects of human activity on river processes. Glaciofluvial landforms include a variety of glacial meltwater channels southwest of Keld, kames and kettle holes around Angram and Thwaite and kame terraces west of Muker. Evidence for climatically driven changes of river activity include a debris flow fan at Hartlakes, and river terraces along the Swale upstream of West Stonesdale Beck. Landforms produced by slope failure include a deep rotational slip at Hooker Mill, a massive debris slide on the northwest side of Kisdon, a massive debris flow at Usha Gap and a block glide at Birk Hill. In the upper part of Skeb Skeugh fine-grained lake sediments below the valley bottom preserve the record of Devensian Lateglacial and Holocene vegetational change, soil development and slope stability. In addition, river landforms show the effects of rock control, of human activity in determining sediment loads, and intrinsic within-channel processes resulting in the formation of large-scale boulder bedforms. The river terraces upstream of Kisdon Force have an extent and elevation determined by rock hardness. Those around Thwaite show the effects of reduced discharge of the present rivers relative to the discharges of the rivers that formed the main valley bottom floodplain slopes, while the impressive array of valley bottom terraces south of Hartlakes are the product of within-channel processes enhanced by sediment yield from the local lead mines.
  
 
Meltwater channels, '''drift''' tails, '''drumlins''' and striations provide the main evidence that glaciation of the region was from the west, and an explanation for the anomalous valley pattern of the Swale and Skeb Skeugh and the origin of Kisdon hill. Meltwater channels indicate that prior to the final melting of this ice sheet, drainage was through Skeb Skeugh and the area between Keld and Hartlakes was an interfluve between the Swale and Swinner Gill. The present valley between these points is ascribed to glacial erosion in response to structural weakness and relatively high glacier energy determined by a steep ice-surface gradient. The kame terraces at Muker indicate a temporary ice-dammed lake between an ice lobe in the Swale valley and a lobe in the Muker Beck valley, and dead ice topography around Angram indicates local ice stagnation. This episode of glaciation was during the Dimlington Stadial (26&nbsp;000–13&nbsp;000 <sup>14</sup>C yrs BP) of the Late Devensian Glaciation and ice wastage across the region occurred about 14&nbsp;000 <sup>14</sup>C yrs BP.
 
Meltwater channels, '''drift''' tails, '''drumlins''' and striations provide the main evidence that glaciation of the region was from the west, and an explanation for the anomalous valley pattern of the Swale and Skeb Skeugh and the origin of Kisdon hill. Meltwater channels indicate that prior to the final melting of this ice sheet, drainage was through Skeb Skeugh and the area between Keld and Hartlakes was an interfluve between the Swale and Swinner Gill. The present valley between these points is ascribed to glacial erosion in response to structural weakness and relatively high glacier energy determined by a steep ice-surface gradient. The kame terraces at Muker indicate a temporary ice-dammed lake between an ice lobe in the Swale valley and a lobe in the Muker Beck valley, and dead ice topography around Angram indicates local ice stagnation. This episode of glaciation was during the Dimlington Stadial (26&nbsp;000–13&nbsp;000 <sup>14</sup>C yrs BP) of the Late Devensian Glaciation and ice wastage across the region occurred about 14&nbsp;000 <sup>14</sup>C yrs BP.

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