Geology of the Bath area: Quaternary - Revision history

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	===Superficial structures and mass-movement deposits===		===Superficial structures and mass-movement deposits===
	Along the escarpment and in the valleys of the Cotswolds, slopes have been extensively affected by superficial disturbances dating from Pleistocene times to the present. Within the district there are many areas where strata capping slopes and hills have begun to tilt or move downslope as blocks, due to the deformation of underlying, less competent mudstone/clay beds that have become ductile (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008">Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. The process, known as cambering, particularly affects slopes in the Fuller’s Earth Formation and Lias Group rocks, which are capped by the Chalfield Oolite Formation or Inferior Oolite Group respectively '''(~~Figure P785917~~, 6).''' Cambered masses that have not become clearly detached from their parent bedrock outcrops (and thus included in landslides) typically have poorly defined lateral extents, and consequently are not distinguished on the geological map. The early stages of cambering lead to the development of large, joint-bounded blocks of limestone, with extensional downslope movement opening the joints and leading to the development of cavities (known as gulls) between blocks (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008"></ref>. Most of the gulls are subsequently partly or wholly filled with rubble, soil or other deposits. Gulls present a significant geological hazard (see Applied geology), and although their overall distribution is poorly known, numerous gulls have been recorded within the district. They may be up to ten metres deep, two metres wide, and several tens of metres long. Where slippage occurs along the interface between the thick beds of the Chalfield Oolite, permitting lower blocks to move, closely spaced open gulls may be present up to 20 metres below ground surface and some distance in from the valley side; gull caves may develop and extend for several hundred metres (Self, 1986<ref>Self, C A. 1986 (for 1985). Two gull caves from the Wiltshire/Avon border. ''Proceedings of the University of Bristol Spelaeological Society'', Vol. 17, 153–174.</ref>; 1995<ref name="Self, 1995"></ref>; Self and Boycott, 2000)<ref>Self, C A, and Boycott, A. 2000 (for 1999). Landslip caves of the southern Cotswolds. ''Proceedings of the University of Bristol Spelae-ological Society'', Vol. 21, 197–214.</ref>.		Along the escarpment and in the valleys of the Cotswolds, slopes have been extensively affected by superficial disturbances dating from Pleistocene times to the present. Within the district there are many areas where strata capping slopes and hills have begun to tilt or move downslope as blocks, due to the deformation of underlying, less competent mudstone/clay beds that have become ductile (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008">Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. The process, known as cambering, particularly affects slopes in the Fuller’s Earth Formation and Lias Group rocks, which are capped by the Chalfield Oolite Formation or Inferior Oolite Group respectively '''(P785917, 6).''' Cambered masses that have not become clearly detached from their parent bedrock outcrops (and thus included in landslides) typically have poorly defined lateral extents, and consequently are not distinguished on the geological map. The early stages of cambering lead to the development of large, joint-bounded blocks of limestone, with extensional downslope movement opening the joints and leading to the development of cavities (known as gulls) between blocks (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008"></ref>. Most of the gulls are subsequently partly or wholly filled with rubble, soil or other deposits. Gulls present a significant geological hazard (see Applied geology), and although their overall distribution is poorly known, numerous gulls have been recorded within the district. They may be up to ten metres deep, two metres wide, and several tens of metres long. Where slippage occurs along the interface between the thick beds of the Chalfield Oolite, permitting lower blocks to move, closely spaced open gulls may be present up to 20 metres below ground surface and some distance in from the valley side; gull caves may develop and extend for several hundred metres (Self, 1986<ref>Self, C A. 1986 (for 1985). Two gull caves from the Wiltshire/Avon border. ''Proceedings of the University of Bristol Spelaeological Society'', Vol. 17, 153–174.</ref>; 1995<ref name="Self, 1995"></ref>; Self and Boycott, 2000)<ref>Self, C A, and Boycott, A. 2000 (for 1999). Landslip caves of the southern Cotswolds. ''Proceedings of the University of Bristol Spelae-ological Society'', Vol. 21, 197–214.</ref>.

	Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. ''Philosophical Transactions of the Royal Society of London Series A'', Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.		Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. ''Philosophical Transactions of the Royal Society of London Series A'', Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.

	Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(~~Figure P785917~~)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref name="Anson et al, 2002">Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. ''Bulletin of Engineering Geology and the Environment'', Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group '''(see table below)'''. The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. ''Proceedings of the 23rd International Geological Congress, Czechoslovakia'', Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref name="Anson et al, 2002"></ref> and landslides continue to present a hazard within the district (see Applied geology).		Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref name="Anson et al, 2002">Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. ''Bulletin of Engineering Geology and the Environment'', Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group '''(see table below)'''. The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. ''Proceedings of the 23rd International Geological Congress, Czechoslovakia'', Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref name="Anson et al, 2002"></ref> and landslides continue to present a hazard within the district (see Applied geology).

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	The Quaternary deposits of the district comprise unlithified (‘superficial’) sedimentary materials laid down during the Pleistocene (2.6 to 0.01 Ma) and Holocene (to present). During the Pleistocene, the British Isles experienced repeated episodes of glaciation, but generally the Bath district is thought to have lain well beyond the maximum ice limits. Consequently, the Quaternary is represented almost entirely by deposits which accumulated through periglacial and fluvial processes.		The Quaternary deposits of the district comprise unlithified (‘superficial’) sedimentary materials laid down during the Pleistocene (2.6 to 0.01 Ma) and Holocene (to present). During the Pleistocene, the British Isles experienced repeated episodes of glaciation, but generally the Bath district is thought to have lain well beyond the maximum ice limits. Consequently, the Quaternary is represented almost entirely by deposits which accumulated through periglacial and fluvial processes.

	However, isolated high-level deposits of gravelly sandy clay with flint, quartz, chert and other exotic pebbles occur around Bath, including at up to 175 m OD south-west of Claverton, and as fissure-fills in the Chalfield Oolite (Donovan, 1995)<ref>Donovan, D T. 1995. High level drift deposits east of Bath. ~~Proceedings~~ of the University of Bristol Spelaeological Society, Vol. 20, 109–126.</ref>. These are thought to be material deposited either by outwash or by fluvial reworking of remanié till, predating the incision of the Avon valley probably before 0.35 Ma (mid Mid Pleistocene) times (Self, 1995)<ref name="Self, 1995">Self, C A. 1995. The relationship between the gull cave Sally’s Rift and the development of the river Avon east of Bath. ~~Proceedings~~ of the University of Bristol Spelaeological Society, Vol. 20, 91–102.</ref>, and indicating that an early Mid Pleistocene ice-sheet may have encroached on the Bath district (Hunt, 1998)<ref>Hunt, C O. 1998. The Quaternary history of the Avon valley and Bristol district. Chapter 10 in Quaternary of south-west England. Campbell, S, Hunt, C O, Scourse, J D, Keen, D H, and Stephens, N (editors). ~~Geological~~ Conservation Review Series, No. 14. (London: Chapman and Hall.)</ref>. These are termed the Bathampton Down Member (BD) of the Kenn Formation (Campbell et al. in Bowen, 1999)<ref name="Bowen, 1999">Bowen, D Q (editor). 1999. A revised correlation of Quaternary deposits in the British Isles. ~~Special~~ Report of the Geological Society of London, No. 23.</ref>.		However, isolated high-level deposits of gravelly sandy clay with flint, quartz, chert and other exotic pebbles occur around Bath, including at up to 175 m OD south-west of Claverton, and as fissure-fills in the Chalfield Oolite (Donovan, 1995)<ref>Donovan, D T. 1995. High level drift deposits east of Bath. ''Proceedings of the University of Bristol Spelaeological Society'', Vol. 20, 109–126.</ref>. These are thought to be material deposited either by outwash or by fluvial reworking of remanié till, predating the incision of the Avon valley probably before 0.35 Ma (mid Mid Pleistocene) times (Self, 1995)<ref name="Self, 1995">Self, C A. 1995. The relationship between the gull cave Sally’s Rift and the development of the river Avon east of Bath. ''Proceedings of the University of Bristol Spelaeological Society'', Vol. 20, 91–102.</ref>, and indicating that an early Mid Pleistocene ice-sheet may have encroached on the Bath district (Hunt, 1998)<ref>Hunt, C O. 1998. The Quaternary history of the Avon valley and Bristol district. Chapter 10 in Quaternary of south-west England. Campbell, S, Hunt, C O, Scourse, J D, Keen, D H, and Stephens, N (editors). ''Geological Conservation Review Series'', No. 14. (London: Chapman and Hall.)</ref>. These are termed the Bathampton Down Member (BD) of the Kenn Formation (Campbell et al. in Bowen, 1999)<ref name="Bowen, 1999">Bowen, D Q (editor). 1999. A revised correlation of Quaternary deposits in the British Isles. ''Special Report of the Geological Society of London'', No. 23.</ref>.

	The modern River Avon is flanked along much of its course by river terrace deposits which represent abandoned floodplains. They are the Bristol Avon Valley Formation, of Mid Pleistocene age, and consist of clay, silt and sand overlying gravel, and three levels can be identified(). However, the unified Avon scheme of Campbell et al. (in Bowen, 1999)<ref name="Bowen, 1999"></ref>, with named Bathampton, Stidham and Ham Green members, is not adopted herein as it fails to allow adequately for the influence of the Hanham and Clifton gorges.		The modern River Avon is flanked along much of its course by river terrace deposits which represent abandoned floodplains. They are the Bristol Avon Valley Formation, of Mid Pleistocene age, and consist of clay, silt and sand overlying gravel, and three levels can be identified(). However, the unified Avon scheme of Campbell et al. (in Bowen, 1999)<ref name="Bowen, 1999"></ref>, with named Bathampton, Stidham and Ham Green members, is not adopted herein as it fails to allow adequately for the influence of the Hanham and Clifton gorges.
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	===Superficial structures and mass-movement deposits===		===Superficial structures and mass-movement deposits===
	Along the escarpment and in the valleys of the Cotswolds, slopes have been extensively affected by superficial disturbances dating from Pleistocene times to the present. Within the district there are many areas where strata capping slopes and hills have begun to tilt or move downslope as blocks, due to the deformation of underlying, less competent mudstone/clay beds that have become ductile (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008">Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. The process, known as cambering, particularly affects slopes in the Fuller’s Earth Formation and Lias Group rocks, which are capped by the Chalfield Oolite Formation or Inferior Oolite Group respectively '''(Figure P785917, 6).''' Cambered masses that have not become clearly detached from their parent bedrock outcrops (and thus included in landslides) typically have poorly defined lateral extents, and consequently are not distinguished on the geological map. The early stages of cambering lead to the development of large, joint-bounded blocks of limestone, with extensional downslope movement opening the joints and leading to the development of cavities (known as gulls) between blocks (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008"></ref>. Most of the gulls are subsequently partly or wholly filled with rubble, soil or other deposits. Gulls present a significant geological hazard (see Applied geology), and although their overall distribution is poorly known, numerous gulls have been recorded within the district. They may be up to ten metres deep, two metres wide, and several tens of metres long. Where slippage occurs along the interface between the thick beds of the Chalfield Oolite, permitting lower blocks to move, closely spaced open gulls may be present up to 20 metres below ground surface and some distance in from the valley side; gull caves may develop and extend for several hundred metres (Self, 1986<ref>Self, C A. 1986 (for 1985). Two gull caves from the Wiltshire/Avon border. ~~Proceedings~~ of the University of Bristol Spelaeological Society, Vol. 17, 153–174.</ref>; 1995<ref name="Self, 1995"></ref>; Self and Boycott, 2000)<ref>Self, C A, and Boycott, A. 2000 (for 1999). Landslip caves of the southern Cotswolds. Proceedings of the University of Bristol Spelae-ological Society, Vol. 21, 197–214.</ref>.		Along the escarpment and in the valleys of the Cotswolds, slopes have been extensively affected by superficial disturbances dating from Pleistocene times to the present. Within the district there are many areas where strata capping slopes and hills have begun to tilt or move downslope as blocks, due to the deformation of underlying, less competent mudstone/clay beds that have become ductile (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008">Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. The process, known as cambering, particularly affects slopes in the Fuller’s Earth Formation and Lias Group rocks, which are capped by the Chalfield Oolite Formation or Inferior Oolite Group respectively '''(Figure P785917, 6).''' Cambered masses that have not become clearly detached from their parent bedrock outcrops (and thus included in landslides) typically have poorly defined lateral extents, and consequently are not distinguished on the geological map. The early stages of cambering lead to the development of large, joint-bounded blocks of limestone, with extensional downslope movement opening the joints and leading to the development of cavities (known as gulls) between blocks (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008"></ref>. Most of the gulls are subsequently partly or wholly filled with rubble, soil or other deposits. Gulls present a significant geological hazard (see Applied geology), and although their overall distribution is poorly known, numerous gulls have been recorded within the district. They may be up to ten metres deep, two metres wide, and several tens of metres long. Where slippage occurs along the interface between the thick beds of the Chalfield Oolite, permitting lower blocks to move, closely spaced open gulls may be present up to 20 metres below ground surface and some distance in from the valley side; gull caves may develop and extend for several hundred metres (Self, 1986<ref>Self, C A. 1986 (for 1985). Two gull caves from the Wiltshire/Avon border. ''Proceedings of the University of Bristol Spelaeological Society'', Vol. 17, 153–174.</ref>; 1995<ref name="Self, 1995"></ref>; Self and Boycott, 2000)<ref>Self, C A, and Boycott, A. 2000 (for 1999). Landslip caves of the southern Cotswolds. ''Proceedings of the University of Bristol Spelae-ological Society'', Vol. 21, 197–214.</ref>.

	Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. ~~Philosophical~~ Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.		Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. ''Philosophical Transactions of the Royal Society of London Series A'', Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.

	Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(Figure P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref name="Anson et al, 2002">Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. ~~Bulletin~~ of Engineering Geology and the Environment, Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group '''(see table below)'''. The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. ~~Proceedings~~ of the 23rd International Geological Congress, Czechoslovakia, Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref name="Anson et al, 2002"></ref> and landslides continue to present a hazard within the district (see Applied geology).		Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(Figure P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref name="Anson et al, 2002">Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. ''Bulletin of Engineering Geology and the Environment'', Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group '''(see table below)'''. The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. ''Proceedings of the 23rd International Geological Congress, Czechoslovakia'', Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref name="Anson et al, 2002"></ref> and landslides continue to present a hazard within the district (see Applied geology).

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	<References/>		<References/>

	== Geology of the Bath area - contents ==		== Geology of the Bath area — contents ==
	{{Bathpapges}}		{{Bathpapges}}

	[[category:Bath - the geology of the area\| 008]]		[[category:Bath - the geology of the area\| 008]]

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	==References==		==References==
	{{~~reflist~~}}		<References/>

			== Geology of the Bath area - contents ==
			{{Bathpapges}}

	[[category:Bath - the geology of the area\| 008]]		[[category:Bath - the geology of the area\| 008]]

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			__NOTOC__
	{{BathSE}}		{{BathSE}}
	The Quaternary deposits of the district comprise unlithified (‘superficial’) sedimentary materials laid down during the Pleistocene (2.6 to 0.01 Ma) and Holocene (to present). During the Pleistocene, the British Isles experienced repeated episodes of glaciation, but generally the Bath district is thought to have lain well beyond the maximum ice limits. Consequently, the Quaternary is represented almost entirely by deposits which accumulated through periglacial and fluvial processes.		The Quaternary deposits of the district comprise unlithified (‘superficial’) sedimentary materials laid down during the Pleistocene (2.6 to 0.01 Ma) and Holocene (to present). During the Pleistocene, the British Isles experienced repeated episodes of glaciation, but generally the Bath district is thought to have lain well beyond the maximum ice limits. Consequently, the Quaternary is represented almost entirely by deposits which accumulated through periglacial and fluvial processes.

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	===Superficial structures and mass-movement deposits===		===Superficial structures and mass-movement deposits===
	Along the escarpment and in the valleys of the Cotswolds, slopes have been extensively affected by superficial disturbances dating from Pleistocene times to the present. Within the district there are many areas where strata capping slopes and hills have begun to tilt or move downslope as blocks, due to the deformation of underlying, less competent mudstone/clay beds that have become ductile (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008">Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. The process, known as cambering, particularly affects slopes in the Fuller’s Earth Formation and Lias Group rocks, which are capped by the Chalfield Oolite Formation or Inferior Oolite Group respectively '''(Figure P785917, 6).''' Cambered masses that have not become clearly detached from their parent bedrock outcrops (and thus included in landslides) typically have poorly defined lateral extents, and consequently are not distinguished on the geological map. The early stages of cambering lead to the development of large, joint-bounded blocks of limestone, with extensional downslope movement opening the joints and leading to the development of cavities (known as gulls) between blocks (Hobbs and Jenkins, 2008)<ref>Hobbs, ~~P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.~~</ref>. Most of the gulls are subsequently partly or wholly filled with rubble, soil or other deposits. Gulls present a significant geological hazard (see Applied geology), and although their overall distribution is poorly known, numerous gulls have been recorded within the district. They may be up to ten metres deep, two metres wide, and several tens of metres long. Where slippage occurs along the interface between the thick beds of the Chalfield Oolite, permitting lower blocks to move, closely spaced open gulls may be present up to 20 metres below ground surface and some distance in from the valley side; gull caves may develop and extend for several hundred metres (Self, 1986<ref>Self, C A. 1986 (for 1985). Two gull caves from the Wiltshire/Avon border. Proceedings of the University of Bristol Spelaeological Society, Vol. 17, 153–174.</ref>; 1995<ref name="Self, 1995"></ref>; Self and Boycott, 2000)<ref>Self, C A, and Boycott, A. 2000 (for 1999). Landslip caves of the southern Cotswolds. Proceedings of the University of Bristol Spelae-ological Society, Vol. 21, 197–214.</ref>.		Along the escarpment and in the valleys of the Cotswolds, slopes have been extensively affected by superficial disturbances dating from Pleistocene times to the present. Within the district there are many areas where strata capping slopes and hills have begun to tilt or move downslope as blocks, due to the deformation of underlying, less competent mudstone/clay beds that have become ductile (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008">Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. The process, known as cambering, particularly affects slopes in the Fuller’s Earth Formation and Lias Group rocks, which are capped by the Chalfield Oolite Formation or Inferior Oolite Group respectively '''(Figure P785917, 6).''' Cambered masses that have not become clearly detached from their parent bedrock outcrops (and thus included in landslides) typically have poorly defined lateral extents, and consequently are not distinguished on the geological map. The early stages of cambering lead to the development of large, joint-bounded blocks of limestone, with extensional downslope movement opening the joints and leading to the development of cavities (known as gulls) between blocks (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008"></ref>. Most of the gulls are subsequently partly or wholly filled with rubble, soil or other deposits. Gulls present a significant geological hazard (see Applied geology), and although their overall distribution is poorly known, numerous gulls have been recorded within the district. They may be up to ten metres deep, two metres wide, and several tens of metres long. Where slippage occurs along the interface between the thick beds of the Chalfield Oolite, permitting lower blocks to move, closely spaced open gulls may be present up to 20 metres below ground surface and some distance in from the valley side; gull caves may develop and extend for several hundred metres (Self, 1986<ref>Self, C A. 1986 (for 1985). Two gull caves from the Wiltshire/Avon border. Proceedings of the University of Bristol Spelaeological Society, Vol. 17, 153–174.</ref>; 1995<ref name="Self, 1995"></ref>; Self and Boycott, 2000)<ref>Self, C A, and Boycott, A. 2000 (for 1999). Landslip caves of the southern Cotswolds. Proceedings of the University of Bristol Spelae-ological Society, Vol. 21, 197–214.</ref>.

	Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. Philosophical Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.		Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. Philosophical Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.

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	The Quaternary deposits of the district comprise unlithified (‘superficial’) sedimentary materials laid down during the Pleistocene (2.6 to 0.01 Ma) and Holocene (to present). During the Pleistocene, the British Isles experienced repeated episodes of glaciation, but generally the Bath district is thought to have lain well beyond the maximum ice limits. Consequently, the Quaternary is represented almost entirely by deposits which accumulated through periglacial and fluvial processes.		The Quaternary deposits of the district comprise unlithified (‘superficial’) sedimentary materials laid down during the Pleistocene (2.6 to 0.01 Ma) and Holocene (to present). During the Pleistocene, the British Isles experienced repeated episodes of glaciation, but generally the Bath district is thought to have lain well beyond the maximum ice limits. Consequently, the Quaternary is represented almost entirely by deposits which accumulated through periglacial and fluvial processes.

	However, isolated high-level deposits of gravelly sandy clay with flint, quartz, chert and other exotic pebbles occur around Bath, including at up to 175 m OD south-west of Claverton, and as fissure-fills in the Chalfield Oolite (Donovan, 1995)<ref>Donovan, D T. 1995. High level drift deposits east of Bath. Proceedings of the University of Bristol Spelaeological Society, Vol. 20, 109–126.</ref>. These are thought to be material deposited either by outwash or by fluvial reworking of remanié till, predating the incision of the Avon valley probably before 0.35 Ma (mid Mid Pleistocene) times (Self, 1995)<ref>Self, C A. 1995. The relationship between the gull cave Sally’s Rift and the development of the river Avon east of Bath. Proceedings of the University of Bristol Spelaeological Society, Vol. 20, 91–102.</ref>, and indicating that an early Mid Pleistocene ice-sheet may have encroached on the Bath district (Hunt, 1998)<ref>Hunt, C O. 1998. The Quaternary history of the Avon valley and Bristol district. Chapter 10 in Quaternary of south-west England. Campbell, S, Hunt, C O, Scourse, J D, Keen, D H, and Stephens, N (editors). Geological Conservation Review Series, No. 14. (London: Chapman and Hall.)</ref>. These are termed the Bathampton Down Member (BD) of the Kenn Formation (Campbell et al. in Bowen, 1999)<ref>Bowen, D Q (editor). 1999. A revised correlation of Quaternary deposits in the British Isles. Special Report of the Geological Society of London, No. 23.</ref>.		However, isolated high-level deposits of gravelly sandy clay with flint, quartz, chert and other exotic pebbles occur around Bath, including at up to 175 m OD south-west of Claverton, and as fissure-fills in the Chalfield Oolite (Donovan, 1995)<ref>Donovan, D T. 1995. High level drift deposits east of Bath. Proceedings of the University of Bristol Spelaeological Society, Vol. 20, 109–126.</ref>. These are thought to be material deposited either by outwash or by fluvial reworking of remanié till, predating the incision of the Avon valley probably before 0.35 Ma (mid Mid Pleistocene) times (Self, 1995)<ref name="Self, 1995">Self, C A. 1995. The relationship between the gull cave Sally’s Rift and the development of the river Avon east of Bath. Proceedings of the University of Bristol Spelaeological Society, Vol. 20, 91–102.</ref>, and indicating that an early Mid Pleistocene ice-sheet may have encroached on the Bath district (Hunt, 1998)<ref>Hunt, C O. 1998. The Quaternary history of the Avon valley and Bristol district. Chapter 10 in Quaternary of south-west England. Campbell, S, Hunt, C O, Scourse, J D, Keen, D H, and Stephens, N (editors). Geological Conservation Review Series, No. 14. (London: Chapman and Hall.)</ref>. These are termed the Bathampton Down Member (BD) of the Kenn Formation (Campbell et al. in Bowen, 1999)<ref name="Bowen, 1999">Bowen, D Q (editor). 1999. A revised correlation of Quaternary deposits in the British Isles. Special Report of the Geological Society of London, No. 23.</ref>.

	The modern River Avon is flanked along much of its course by river terrace deposits which represent abandoned floodplains. They are the Bristol Avon Valley Formation, of Mid Pleistocene age, and consist of clay, silt and sand overlying gravel, and three levels can be identified(). However, the unified Avon scheme of Campbell et al. (in Bowen, 1999)<ref>Bowen, ~~D Q (editor). 1999. A revised correlation of Quaternary deposits in the British Isles. Special Report of the Geological Society of London, No. 23.~~</ref>, with named Bathampton, Stidham and Ham Green members, is not adopted herein as it fails to allow adequately for the influence of the Hanham and Clifton gorges.		The modern River Avon is flanked along much of its course by river terrace deposits which represent abandoned floodplains. They are the Bristol Avon Valley Formation, of Mid Pleistocene age, and consist of clay, silt and sand overlying gravel, and three levels can be identified(). However, the unified Avon scheme of Campbell et al. (in Bowen, 1999)<ref name="Bowen, 1999"></ref>, with named Bathampton, Stidham and Ham Green members, is not adopted herein as it fails to allow adequately for the influence of the Hanham and Clifton gorges.

	The active floodplains of the Avon and its tributaries are underlain by alluvium (), which comprises clay, silt, sand and gravel, in places with beds or lenses of peat. On the east bank of the Avon at Warleigh Wood, narrow tributaries running over limestone bedrock have deposited small spreads of calcareous tufa (). More widely across the district, slopes are commonly mantled with a discontinuous veneer of head deposits (), which represent slope-wash and colluvial materials, deposited both under periglacial conditions in the Pleistocene and under broadly modern climatic conditions in the Holocene. They consist of gravel, sand, silt and clay in variable proportions, reflecting the composition of the geological materials upslope.		The active floodplains of the Avon and its tributaries are underlain by alluvium (), which comprises clay, silt, sand and gravel, in places with beds or lenses of peat. On the east bank of the Avon at Warleigh Wood, narrow tributaries running over limestone bedrock have deposited small spreads of calcareous tufa (). More widely across the district, slopes are commonly mantled with a discontinuous veneer of head deposits (), which represent slope-wash and colluvial materials, deposited both under periglacial conditions in the Pleistocene and under broadly modern climatic conditions in the Holocene. They consist of gravel, sand, silt and clay in variable proportions, reflecting the composition of the geological materials upslope.
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	===Superficial structures and mass-movement deposits===		===Superficial structures and mass-movement deposits===
	Along the escarpment and in the valleys of the Cotswolds, slopes have been extensively affected by superficial disturbances dating from Pleistocene times to the present. Within the district there are many areas where strata capping slopes and hills have begun to tilt or move downslope as blocks, due to the deformation of underlying, less competent mudstone/clay beds that have become ductile (Hobbs and Jenkins, 2008)<ref>Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. The process, known as cambering, particularly affects slopes in the Fuller’s Earth Formation and Lias Group rocks, which are capped by the Chalfield Oolite Formation or Inferior Oolite Group respectively '''(Figure P785917, 6).''' Cambered masses that have not become clearly detached from their parent bedrock outcrops (and thus included in landslides) typically have poorly defined lateral extents, and consequently are not distinguished on the geological map. The early stages of cambering lead to the development of large, joint-bounded blocks of limestone, with extensional downslope movement opening the joints and leading to the development of cavities (known as gulls) between blocks (Hobbs and Jenkins, 2008)<ref>Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. Most of the gulls are subsequently partly or wholly filled with rubble, soil or other deposits. Gulls present a significant geological hazard (see Applied geology), and although their overall distribution is poorly known, numerous gulls have been recorded within the district. They may be up to ten metres deep, two metres wide, and several tens of metres long. Where slippage occurs along the interface between the thick beds of the Chalfield Oolite, permitting lower blocks to move, closely spaced open gulls may be present up to 20 metres below ground surface and some distance in from the valley side; gull caves may develop and extend for several hundred metres (Self, 1986<ref>Self, C A. 1986 (for 1985). Two gull caves from the Wiltshire/Avon border. Proceedings of the University of Bristol Spelaeological Society, Vol. 17, 153–174.</ref>; 1995<ref>Self, C A. 1995. The relationship between the gull cave Sally’s Rift and the development of the river Avon east of Bath. Proceedings of the University of Bristol Spelaeological Society, Vol. 20, 91–102.</ref>; Self and Boycott, 2000)<ref>Self, C A, and Boycott, A. 2000 (for 1999). Landslip caves of the southern Cotswolds. Proceedings of the University of Bristol Spelae-ological Society, Vol. 21, 197–214.</ref>.		Along the escarpment and in the valleys of the Cotswolds, slopes have been extensively affected by superficial disturbances dating from Pleistocene times to the present. Within the district there are many areas where strata capping slopes and hills have begun to tilt or move downslope as blocks, due to the deformation of underlying, less competent mudstone/clay beds that have become ductile (Hobbs and Jenkins, 2008)<ref name="Hobbs et al, 2008">Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. The process, known as cambering, particularly affects slopes in the Fuller’s Earth Formation and Lias Group rocks, which are capped by the Chalfield Oolite Formation or Inferior Oolite Group respectively '''(Figure P785917, 6).''' Cambered masses that have not become clearly detached from their parent bedrock outcrops (and thus included in landslides) typically have poorly defined lateral extents, and consequently are not distinguished on the geological map. The early stages of cambering lead to the development of large, joint-bounded blocks of limestone, with extensional downslope movement opening the joints and leading to the development of cavities (known as gulls) between blocks (Hobbs and Jenkins, 2008)<ref>Hobbs, P R N, and Jenkins, G O. 2008. Bath’s ‘foundered strata’ — a re-interpretation. British Geological Survey Open Report, OR/08/052.</ref>. Most of the gulls are subsequently partly or wholly filled with rubble, soil or other deposits. Gulls present a significant geological hazard (see Applied geology), and although their overall distribution is poorly known, numerous gulls have been recorded within the district. They may be up to ten metres deep, two metres wide, and several tens of metres long. Where slippage occurs along the interface between the thick beds of the Chalfield Oolite, permitting lower blocks to move, closely spaced open gulls may be present up to 20 metres below ground surface and some distance in from the valley side; gull caves may develop and extend for several hundred metres (Self, 1986<ref>Self, C A. 1986 (for 1985). Two gull caves from the Wiltshire/Avon border. Proceedings of the University of Bristol Spelaeological Society, Vol. 17, 153–174.</ref>; 1995<ref name="Self, 1995"></ref>; Self and Boycott, 2000)<ref>Self, C A, and Boycott, A. 2000 (for 1999). Landslip caves of the southern Cotswolds. Proceedings of the University of Bristol Spelae-ological Society, Vol. 21, 197–214.</ref>.

	Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. Philosophical Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.		Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. Philosophical Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.

	Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(Figure P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group '''(see table below)'''. The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. Proceedings of the 23rd International Geological Congress, Czechoslovakia, Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref> and landslides continue to present a hazard within the district (see Applied geology).		Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(Figure P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref name="Anson et al, 2002">Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group '''(see table below)'''. The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. Proceedings of the 23rd International Geological Congress, Czechoslovakia, Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref name="Anson et al, 2002"></ref> and landslides continue to present a hazard within the district (see Applied geology).

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	{{reflist}}		{{reflist}}

	[[category:Bath - the geology of the area\| ~~006~~]]		[[category:Bath - the geology of the area\| 008]]

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	Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. Philosophical Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.		Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. Philosophical Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.

	Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(Figure P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group (see table below). The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. Proceedings of the 23rd International Geological Congress, Czechoslovakia, Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref> and landslides continue to present a hazard within the district (see Applied geology).		Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(Figure P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group '''(see table below)'''. The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. Proceedings of the 23rd International Geological Congress, Czechoslovakia, Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref> and landslides continue to present a hazard within the district (see Applied geology).

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Dbk at 10:57, 7 July 2014

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	Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. Philosophical Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.		Cambering is thought to take place largely under glacial or periglacial conditions (Forster et al., 1985)<ref>Forster, A, Hobbs, P R N, Monkhouse, R A, and Wyatt, R J. 1985. An environmental geology study of parts of West Wiltshire and south-east Avon. British Geological Survey Technical Report, WA/85/25.</ref>. Cambered strata are overlain by river terrace deposits at Twerton (Chandler et al., 1976)<ref>Chandler, R J, Kellaway, G A, Skempton, A W, and Wyatt, R J. 1976. Valley slope sections in some Jurassic strata near Bath, Somerset. Philosophical Transactions of the Royal Society of London Series A, Vol. 283, 527–556.</ref> indicating that at least some movements are ancient. It is not thought that cambering is active here under the present temperate climate, although landslides that are more recent commonly incorporate cambered (e.g. block-toppled) material.

	Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(Figure P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group ~~'''~~(~~Figure 6~~).~~'''~~ The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. Proceedings of the 23rd International Geological Congress, Czechoslovakia, Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref> and landslides continue to present a hazard within the district (see Applied geology).		Discrete areas of mass down-slope movement of rock and/or soil are depicted as landslide deposits, and comprise rock falls, mudflows, and either rotational or translational slides which may include detached cambers '''(Figure P785917)'''. Their formation results from several principal processes, possibly in combination: weathering-induced limestone fragmentation and conversion of mudstone to clay; undercutting or loading of slopes by natural or human actions, and changes in the groundwater regime. An increase in pore water pressure in overconsolidated clay or silt-dominated formations (e.g. Charmouth Mudstone, Bridport Sand, Dyrham, Fuller’s Earth and Oxford Clay) and in overlying fine-grained head deposits, can result in reduced shear strength and relatively shallow failure of the hillslope. This commonly occurs by rotational sliding, or by translational sliding (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref>, particularly within the Fuller’s Earth Formation and Lias Group (see table below). The majority of the landslides within the district are of these types, and probably formed during the wetter, periglacial climate of the latest Pleistocene. Many of the older landslides within the district, including those at Bailbrook [773 673], Beacon Hill [751 659], Beechen Cliff [751 641], Twerton [726 644] and North Stoke [700 687], are large rotational failures on the lower slopes, thought to be initiated by the downcutting of the River Avon, perhaps during the later Pleistocene (Kellaway and Taylor, 1968)<ref>Kellaway, G A, and Taylor, J H. 1968. The influence of landslipping on the development of the city of Bath, England. Proceedings of the 23rd International Geological Congress, Czechoslovakia, Vol. 12, 65–76.</ref>. Minor movements, usually of mudflow or translational type associated with prolonged saturation, continue to the present day (Anson and Hawkins, 2002)<ref>Anson, R, and Hawkins, A B. 2002. Movement of the Soper’s Wood landslide on the Jurassic Fuller’s Earth, Bath, England. Bulletin of Engineering Geology and the Environment, Vol. 61, 325–345.</ref> and landslides continue to present a hazard within the district (see Applied geology).

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Jeth1 at 14:42, 3 July 2014

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	[[Image:P785917.jpg\|thumb\|350px\|Stages of cambering and mass movement of slopes in Middle Jurassic strata in the district. For key to bedrock units, see Geological Description. P785917.]]		[[Image:P785917.jpg\|thumb\|350px\|Stages of cambering and mass movement of slopes in Middle Jurassic strata in the district. For key to bedrock units, see Geological Description. P785917.]]
	~~[[Image:P785918.jpg\|thumb\|350px\|Aeromagnetic anomaly map of the Bath district and adjacent areas. P785918.]]~~

	===Superficial structures and mass-movement deposits===		===Superficial structures and mass-movement deposits===