Myrddyn Phillips - Mapping Mountains: Mapping Mountains – Summit Relocations

Monday, 21 August 2017

Mapping Mountains – Summit Relocations – 500m Twmpau

500m Twmpau – Summit Relocations

The 500m Twmpau (thirty welsh metre prominences and upward) are the Welsh hills at or above 500m and below 600m in height that have a minimum drop of 30m. Accompanying the main P30 list is a sub list entitled the 500m Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop.

The list is authored by Myrddyn Phillips and the posts that have appeared on Mapping Mountains detailing the summit relocations to the main P30 list and the sub list appear below presented chronologically in receding order.

Mapping Mountains - Summit Relocations - 500m Twmpau

Yr Eifl (SH 364 447) - 9th summit relocation

Significant Height Revisions post for Yr Eifl

There has been a Summit Relocation that is retrospective to a hill that is listed in the 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop, the dominance and status of the hill derived from a Leica GS15 summit survey conducted by John Barnard, Graham Jackson and Myrddyn Phillips, and LIDAR bwlch analysis conducted by Aled Williams.

Yr Eifl (SH 364 447)

The criteria for the three listings that this summit relocation applies to are:

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m in height that have 20m or more and below 30m of drop. With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and is published on Mapping Mountains in Google Doc format.

500m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height. The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop. This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Yr Eifl and it is adjoined to its own group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with minor roads to its north-east, the B4417 road to its south and the A499 road to its east, and has the villages of Trefor towards the north north-east and Llithfaen towards the south south-west.

When the listings of the 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru were first compiled, this hill was listed with a summit height of 564m, based on the spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until the survey with the Leica GS15 that the details for this hill could be accurately re-assessed. Although the trig pillar is positioned on a relatively stable base it is positioned on the top of a substantial ancient cairn which consists of a multitude of individual stones and rocks and as this is considered as not being permanent in nature, it is the highest remaining natural ground on the periphery of the ancient cairn that is taken as both its listed summit height and summit position, and when compared to its originally listed summit position this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation, within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or the de-twinning of a summit, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Gathering data with the Leica GS15 at the listed summit position of Yr Eifl

Therefore, the summit height produced by the Leica GS15 survey is 560.7m and this is positioned at SH 36482 44734. This position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, although this position is relatively close to where the triangulation pillar is situated, it is importantly positioned to the highest remaining natural ground on the periphery of the large ancient cairn.

The full details for the hill are:

Group: Yr Eifl

Name: Yr Eifl

OS 1:50,000 map: 123

Summit Height: 560.7m (converted to OSGM15, Leica GS15)

Summit Grid Reference (New Position): SH 36482 44734 (Leica GS15)

Bwlch Height: 129.4m (LIDAR)

Bwlch Grid Reference: SH 45347 48678 (LIDAR)

Drop: 431.3m (Leica GS15 summit and LIDAR bwlch)

Myrddyn Phillips (March 2026)

Mapping Mountains - Summit Relocations - 500m Twmpau

Mynydd Trawsnant (SN 824 485) - 8th summit relocation

There has been a Summit Relocation to a hill that is listed in the 500m Twmpau and the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams.

LIDAR image of Mynydd Trawsnant (SN 824 485)

The criteria for the two listings that this summit relocation applies to are:

The 500m Twmpau by Myrddyn Phillips

Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop. This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Mynydd Trawsnant and it is adjoined to the Drygarn Fawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-west and the A483 road to its south-east, and has the town of Llanwrtyd towards the east south-east.

Extract from the Ordnance Survey 1:25,000 Explorer map

When the original list of Welsh 500m P15s that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 139m of drop based on the 517m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SN 82136 48415, and an estimated c 378m bwlch height.

Extract from the Ordnance Survey 1:50,000 Landranger map

The details for this hill were re-evaluated when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online. This mapping had many spot heights not on other publicly available maps and for this hill it had a 378m bwlch spot height and therefore its drop was amended to 139m.

LIDAR summit image of Mynydd Trawsnant (SN 824 485)

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed. The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Extract from the Ordnance Survey series of Six-Inch maps

The details ascertained from LIDAR for the new and old summit position are given below, but as the upper section of this hill is forested the accuracy of LIDAR modelling may be compromised. However, the pre-forestry levelled height on the Ordnance Survey series of Six-Inch maps substantiates the new LIDAR position.

New summit: 516.559m at SN 82452 48564

Old summit: 516.489m at SN 82162 48430

The above detail compared to the summit position previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to when the high point is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the summit height produced by LIDAR analysis is 516.6m and this is positioned at SN 82452 48564. This position is not given a spot height on the contemporary Ordnance Survey 1:25,000 Explorer map, but is close to where the 517m spot height appears on the contemporary 1:50,000 Landranger map and is approximately 320 metres north-eastward from where the previously listed summit is positioned.

The full details for the hill are:

Group: Drygarn Fawr

Name: Mynydd Trawsnant

OS 1:50,000 map: 147

Summit Height: 516.6m (LIDAR)

Summit Grid Reference (new position): SN 82452 48564 (LIDAR)

Bwlch Height: 378.3m (LIDAR)

Bwlch Grid Reference: SN 82781 50423 (LIDAR)

Drop: 138.3m (LIDAR)

Myrddyn Phillips (August 2023)

Mapping Mountains - Summit Relocations - 500m Twmpau

Foel Fawr (SH 728 392) - 7th summit relocation

Survey post for Foel Fawr

Foel Fawr (SH 728 392)

The criteria for the two listings that this summit relocation applies to are:

The 500m Twmpau by Myrddyn Phillips

Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19th June 2019.

The Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Foel Fawr and it is adjoined to the Arenig Fach group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A2), and it is positioned with the B4391 road to its north, the A470 road to its west and the A4212 road to its south, and has the village of Trawsfynydd towards the south-west.

When the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 41m of drop based on the 528m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SH 72620 39472, and an estimated c 487m bwlch height, based on interpolation of 10m contouring between 480m - 490m.

Extract from the Ordnance Survey 1:25,000 Explorer map

Since first compilation of the Welsh 500m P15 list there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, and it was this map that showed a 528m map heighted twin summit positioned at SH 72873 39268. The two 528m spot heights are also shown on the mapping hosted on the Magic Maps website.

Extract from the Magic Maps website

However, it was not until the survey with the Trimble GeoXH 6000 that the details for this hill could be accurately re-assessed. The height and position for each summit is given below:

South-easterly summit: 528.611m at SH 72872 39284

North-westerly summit: 527.542m at SH 72621 39476

The above detail compared to the prioritised summit previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation, within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or the listing of a new twin summit or de-twinning of a summit, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Gathering data at the higher of the Foel Fawr summits

Gathering data at the lower of the Foel Fawr summits

Therefore, the summit height produced by the Trimble GeoXH 6000 survey is 528.6m and this is positioned at SH 72872 39284, this position is not given a spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, but is given a 528m spot height on the interactive mapping hosted on the Magic Maps website, and is approximately 260 metres south-eastward from where the previously listed and prioritised summit is positioned.

The full details for the hill are:

Group: Arenig Fach

Name: Foel Fawr

OS 1:50,000 map: 124

Summit Height: 528.6m (converted to OSGM15)

Summit Grid Reference (New Position): SH 72872 39284

Bwlch Height: 485.5m (converted to OSGM15)

Bwlch Grid Reference: SH 73074 39525

Drop: 43.1m

Myrddyn Phillips (October 2020)

Mapping Mountains - Summit Relocations - 500m Twmpau

Carreg Croes Ifor (SO 248 106) - 6th summit relocation

Significant Height Revisions post for Carreg Croes Ifor

There has been a Summit Relocation to a hill that is listed in the 500m Twmpau and The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 summit survey conducted by Aled Williams.

LIDAR image of Carreg Croes Ifor (SO 248 106)

The criteria for the two listings that this summit relocation applies to are:

The Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19th June 2019.

The name the hill is listed by is Carreg Croes Ifor and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned with the A465 road to its north, the B4248 road to its south-west and the B4246 road to its east, and has the town of Blaenafon towards the south south-east.

When the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 18m of drop based on a non-interpolated c 500m summit height and a 482m bwlch height taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

Since first compilation of the Welsh 500m P15 list there are a number of maps now available online, and the details for this hill were re-assessed when the Ordnance Survey 1:25,000 Historical map became available online, and this map gives a 1657ft (505.1m) summit spot height for this hill.

Extract from the Ordnance Survey 1:25,000 Historical map

The imperial height on the Ordnance Survey 1:25,000 Historical map is derived from a 1657.4m (505.2m) Surface Height that appears on the Ordnance Survey series of Six-Inch maps. Therefore, the summit height for this hill was revised and listed as 505m with the caveat that since this height was derived this hill has undergone mining activity which has substantially altered the landscape.

Extract from the Ordnance Survey series of Six-Inch maps

LIDAR summit image for Carreg Croes Ifor

The summit height and position produced by LIDAR analysis is 509.8m at SO 24848 10663, and this position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour compared to its previous listed position, or when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.

During analysis of this hill, Aled used overlays from old maps with contemporary maps and the details produced via LIDAR. This shows that the natural 505.2m summit positioned at SO 24810 10620 is now under a substantial amount of mine spoil and this has raised the height of the summit.

The summit of this hill has now been surveyed with the Trimble GeoXH 6000 and as the natural summit is now under a spoil tip and an on-site visit confirms this artificially raised summit to be solid and stable, it is the Trimble summit height and position that is being prioritised for this hill.

Therefore, the new listed summit height for this hill is 509.7m and is positioned at SO 24848 10663, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and is approximately 160 metres westward from where the previously listed summit is positioned.

The full details for the hill are:

Group: Cymoedd Gwent

Name: Carreg Croes Ifor

OS 1:50,000 map: 161

Summit Height: 509.7m (converted to OSGM15, Trimble GeoXH 6000, artificially raised)

Summit Grid Reference (New Position): SO 24848 10663 (Trimble GeoXH 6000)

Bwlch Height: 482.1m (LIDAR)

Bwlch Grid Reference: SO 25485 10565 (LIDAR)

Drop: 27.6m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (May 2020)

Mapping Mountains - Summit Relocations - 500m Twmpau

Cerrig Llwydion (SN 909 731) - 5th summit relocation

There has been confirmation of a Summit Relocation to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, 500m Twmpau and The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Aled Williams.

LIDAR image of Cerrig Llwydion (SN 909 731)

The criteria for the three listings that this summit relocation applies to are:

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill now included in the 500m Sub-Pedwar category. The criteria for 500m Sub-Pedwar status being all Welsh hills at or above 500m and below 510m in height that have 30m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

The name the hill is listed by is Cerrig Llwydion and it is adjoined to the Elenydd group of hills, which are situated in the northern part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the Afon Gwy (River Wye) and the A470 road to its north-east, and has the village of Llangurig towards the north.

When the listing that is now named the 500m Twmpau was first compiled the qualifying hill was listed as Sychnentydd with a 508m summit height based on the spot height that appears on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and which is positioned at SN 909 724. As the adjoining summit of Cerrig Llwydion only had an uppermost 500m ring contour and did not possess a spot height it was regarded as lower in height compared to the adjacent hill of Sychnentydd.

Extract from the Ordnance Survey 1:25,000 Explorer map

It was David Purchase who first brought to attention that Cerrig Llwydion may be higher than Sychnentydd, a rudimentary survey using a basic levelling staff was then conducted by Myrddyn Phillups on the 9^th November 2005 resulting in Cerrig Llwydion being approximately 2m higher than Sychnenydd and with 13m of drop from the connecting bwlch between the two summits to the higher hill. This was followed by an on-site visit from John Kirk who took readings during a basic survey and concluded that Cerrig Llwydion is the higher hill by approximately 1.5m – 2m.

The details for this hill were also re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online. This mapping had many spot heights not on other publicly available Ordnance Survey maps and showed a 509m summit spot height for Cerrig Llwydion. This spot height is also shown on Ordnance Survey data that appears on the Magic Maps website.

Extract from the Magic Maps website

The qualifying summit was subsequently relocated to Cerrig Llwydion based on the rudimentary surveys and the 509m spot height as detailed above.

The LIDAR result for each summit is given below:

Sychnentydd: 508.0m summit at SN 91001 72465

Cerrig Llwydion: 509.4m summit at SN 90965 73141

LIDAR image of Cerrig Llwydion and Sychnentydd

The result produced by LIDAR analysis comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour compared to its previous listed position, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.

Therefore, the summit height produced by LIDAR analysis for Cerrig Llwydion is 509.4m and is positioned at SN 90965 73141, and as this summit has been confirmed as being 1.4m higher than the 508.0m summit of Sychnentydd positioned at SN 91001 72465 the relocation of the qualifying summit is confirmed.

The full details for the hill are:

Group: Elenydd

Name: Cerrig Llwydion

OS 1:50,000 map: 136 147

Summit Height: 509.4m (LIDAR)

Summit Grid Reference (new position): SN 90965 73141 (LIDAR)

Bwlch Height: 462.0m (LIDAR)

Bwlch Grid Reference: SN 92807 72279 (LIDAR)

Drop: 47.4m (LIDAR)

Myrddyn Phillips (February 2020)

Mapping Mountains - Summit Relocations - 500m Twmpau

Cistfaen (SN 867 775) - 4th summit relocation

Survey post for Cistfaen

There has been confirmation of a Summit Relocation to a hill that is listed in the 500m Twmpau and the Yr Uchafion, with the summit height, bwlch height and their locations, drop and status of the hill being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips on the 28^th March 2019, and the height and position of the previously listed summit confirmed by LIDAR analysis conducted by Aled Williams.

Cistfaen (SN 867 775)

The criteria for the two listings that this summit relocation applies to are:

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m in height that have 20m or more and below 30m of drop. With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips.

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4^th November 2015.

The name of the hill is Cistfaen, and it is adjoined to the Elenydd group of hills, which are situated in the central part of Mid and West Wales (Region B, Sub-Region B2), and is positioned with minor roads to its north and south and has the A44 road further to its north and the A470 road to its east, and has the small community of Llangurig and the town of Llanidloes towards the north-east.

When the listing that would later be referred to as Yr Uchafion was first compiled this hill was listed with a summit position placed at SN 86474 77145 based on the 535m spot height that appears on the Ordnance Survey 1:25,000 Explorer map. This position is in a conifer plantation with the Ordnance Survey 1:50,000 Landranger map also giving a 535m spot height to an ancient cairn that is positioned just outside of the conifer plantation.

Extract from the Ordnance Survey 1:25,000 Explorer map

Extract from the Ordnance Survey 1:50,000 Landranger map

This hill’s summit was subsequently relocated to SN 86788 77502 based on the 536m spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

LIDAR only covers the area around the ancient cairn and the 535m map heighted top, and its analysis resulted in the following:

Ancient cairn: 535.0m at SN 86367 77036

535m spot height: 534.9m at SN 86465 77153

The survey with the Trimble GeoXH 6000 at the 536m map heighted summit resulted in the following:

536m spot height: 535.1m at SN 86787 77515

All three results are close in height but as the result produced by the Trimble GeoXH 6000 survey is the highest it is considered the best available evidence for this hill’s summit position and height, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

The Trimble GeoXH 6000 gathering data at the summit of Cistfaen

The summit height produced by the Trimble GeoXH 6000 survey is 535.1m and is positioned at SN 86787 77515. This position is given a 536m spot height on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map and is approximately 450 metres north-eastward from where the previously listed summit position is situated, and approximately 600 metres north-eastward from the ancient cairn that LIDAR analysis gives as 0.1m higher than the original listed summit position.

The full details for the hill are:

Group: Elenydd

Name: Cistfaen

OS 1:50,000 map: 135, 136 147

Summit Height: 535.1m (converted to OSGM15)

Summit Grid Reference (new position): SN 86787 77515

Bwlch Height: 512.9m (converted to OSGM15)

Bwlch Grid Reference: SN 86609 77748

Drop: 22.3m (converted to OSGM15)

For details on the survey of this hill

Myrddyn Phillips (August 2019)

Mapping Mountains - Summit Relocations - 500m Twmpau

Mynydd Ystradffernol (SN 937 009) - 3rd summit relocation

Survey post for Mynydd Ystradffernol

There has been a Summit Relocation to a hill that is listed in the Yr Uchafion and the 500m Twmpau, with the summit height, drop and status of the hill being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips on the 25^th August 2018.

Mynydd Ystradffernol (SN 937 009)

The criteria for the two listings that this summit relocation applies to are:

The name of the hill is Mynydd Ystradffernol, and it is adjoined to the Cymoedd Gwent range of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and is positioned with the A 4061 road to the west and has the village of Treherbert towards the south.

As the summit of the hill is a part of designated open access land it can in theory be approached from any direction. However, the hill is covered in an extensive conifer plantation which over recent years now incorporates many wind turbines. The building of the wind farm has created access tracks and these can be used to ease passage toward the summit.

Prior to the survey with the Trimble GeoXH 6000 the summit of this hill was listed near to where the 518m summit spot height appears on the Ordnance Survey 1:25,000 Explorer map, this position is at SN 93682 00905.

Two surveys were taken with the Trimble GeoXH 6000 with the following results:

1^st survey: 517.808m at SN 93790 00902

2^nd survey: 517.612m at SN 93676 00907

Gathering data at the summit of Mynydd Ystradffernol

The second data set taken for the summit position of Mynydd Ystradffernol

The second survey was taken to the highest ground close to where the 518m spot height appears on the Ordnance Survey 1:25,000 Explorer map. However, the result produced by the Trimble for the first survey is higher and its position comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

Extract from the Ordnance Survey 1:25,000 Explorer map showing the new summit position in relation to the old listed summit position at the 518m spot height

The summit height produced by the Trimble GeoXH 6000 survey is 517.8m and is positioned at SN 93790 00902. This position is not given a spot height on Ordnance Survey maps and is approximately 100 metres east from where the previously listed summit position is situated.

The full details for the hill are:

Group: Cymoedd Gwent

Name: Mynydd Ystradffernol

OS 1:50,000 map: 170

Summit Height: 517.8m (converted to OSGM15)

Summit Grid Reference (new position): SN 93790 00902

Bwlch Height: 484.9m (converted to OSGM15)

Bwlch Grid Reference: SN 92961 02194

Drop: 32.9m (converted to OSGM15)

For details on the survey that confirmed the summit relocation of this hill

Myrddyn Phillips (January 2019)

Mapping Mountains - Summit Relocations - 500m Twmpau

Mynydd Ton (SS 949 940) - 2nd summit relocation

2nd survey post for Mynydd Ton

1st survey post for Mynydd Ton

Significant Height Revisions post for Mynydd Ton

There has been a Summit Relocation initiated by a survey with the Trimble GeoXH 6000 to the listings of Yr Uchafion and the 500m Twmpau, with the survey that resulted in this summit relocation being conducted on the 23^rd July 2016 in good, clear and sheltered conditions.

The two lists that this summit relocation affects are:

Yr Uchafion, this is the working title for a list that takes in all hills in Wales at and above 500m in height that have a minimum 15m of drop. This list is co-authored by Myrddyn Phillips and Aled Williams.

500m Twmpau (thirty welsh metre prominences and upward), with the criteria being all Welsh hills at or above 500m and below 600m in height that have a minimum 30m of drop. This list is authored by Myrddyn Phillips.

The survey was conducted in the range of hills known as the Y Cymoedd, these are the hills associated with the south Wales valleys. The hill is situated between Cwm Ogwr Fawr to its west and the Rhondda Fawr valley to its east and is positioned above the towns of Treorci (Treorchy) and Treherbert to its north and Nant-y-moel, Price Town and Ogmore Vale to its south-west.

Access to the hill is relatively easy as a track leaves the A 4061 near to its high point and continues south-eastward to the north-western edge of a large conifer plantation, a path continues south-eastward adjacent to the forest boundary gaining the access point to a wide forest break which is relatively near the summit of this hill.

The name of the hill is Mynydd Ton and prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 539m at SS 94796 93958 which is beside an ancient cairn. This height was based on a 1,769.3ft surface height given on the Ordnance Survey Six-Inch map published in 1885. The 539m figure was a relatively new addition to this hill’s listed height as its summit position was originally listed as ground beside its map heighted 535m triangulation pillar situated at SS 94931 94058.

The highest ground at the base of and beside the ancient cairn was surveyed with the Trimble GeoXH 6000 as being 534.2m (converted to OSGM15) high. The processed data gave Estimated Accuracies of 5-15cm: 99.41%, with the Standard Deviation being 0.0m, and the margin of uncertainty given for the height placement of the Trimble was 0.1m. All of the above signify that the data set was good and accurate to within the parameters of the equipment.

I had previously visited this hill in February 2003 and judged ground approximately one minute walk away from the trig pillar to be slightly higher than ground at the base of the trig pillar, and as the flush bracket adjoined to the trig pillar is given a height of 535.335m in the OS Trig Database it means that ground at its base is approximately 535m high. This figure is dependent upon the accuracy of the flush bracket height which is given as 3^rd order. Therefore the ground at the base of or near to the triangulation pillar is likely to be higher than that beside the ancient cairn.

Therefore the position of the relocated summit is at SS 94931 94058 and consists of ground at the base of, or near to the triangulation pillar. This re-located summit position is at the hill’s originally listed summit and is given a 535m height on current Ordnance Survey maps and it is approximately 175 metres north-eastward from the previously listed summit position.

The full details for the hill are:

Cardinal Hill: Werfa

Summit Height: 534.4m (converted to OSGM15)

Name: Mynydd Ton

OS 1:50,000 map: 170

Summit Grid Reference (New Position): SS 94931 94059

Drop: 91.3m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data beside the ancient cairn on Mynydd Ton, with the relocated position of the summit approximately 175 metres to the north-east and to the right of the forest break in the centre background of this photograph

For details on the survey that relocated the summit of this hill

For details on the 2nd survey of this hill

Myrddyn Phillips (August 2016)

Mapping Mountains - Summit Relocations - 500m Twmpau

Bryn Llwyd (SN 835 920) - 1st summit relocation

First survey post for Bryn Llwyd

Second survey post for Bryn Llwyd

Significant Name Changes post for Bryn Llwyd

There has been a Summit Relocation initiated by a survey with the Trimble GeoXH 6000 to the listings of Y Pellennig, Yr Uchafion and 500m Twmpau, with the survey that resulted in this summit relocation being conducted on the 5^th and 13^th May 2016.

The three lists that this summit relocation affects are:

Y Pellennig - The Remotest Hills of Wales, with the criteria being all hills in Wales whose summit is 2.5km or more from the nearest paved public road that have a minimum 15m of drop. This list is co-authored by Myrddyn Phillips and Aled Williams.

Yr Uchafion, this is the working title for a list that takes in all hills in Wales at and above 500m in height that have a minimum 15m of drop. This list is co-authored by Myrddyn Phillips and Aled Williams.

500m Twmpau (thirty welsh metre prominences and upward), with the criteria being all Welsh hills at or above 500m and below 600m in height that have a minimum 30m of drop. This list is authored by Myrddyn Phillips.

As the hill only entered the ranks of Pellennig hills due to this survey this listing of hills is being included within this Summit Relocations heading.

The survey was conducted in the Pumlumon range of hills over two beautiful sunny days, with the hill situated mid-way between the towns of Machynlleth to its north-west and Llanidloes to its south-east.

The name of the hill where the summit has been re-located to is Bryn Llwyd (SN 835 920) and the name of the hill where the summit has been re-located from is Bryn yr Ŵyn (SN 839 925). Both summits and respective bylchau were surveyed with the Trimble with their summits being connected by a bwlch that is only 9.9m below the summit height of Bryn yr Ŵyn and 11.4m below the summit height of Bryn Llwyd.

The summits of both hills possess a small uppermost 500m ring contour on Ordnance Survey maps with no adjoined spot height, with the uppermost ring contour for Bryn Llwyd being the larger.

The critical bwlch for the higher of these hills in positioned to the south-west and to my knowledge their drop has only been surveyed on three occasions, once using a basic levelling survey (BLS) method, and the other two using the Trimble GeoXH 6000. The results from each survey appear below:

Bryn Llwyd: summit to critical bwlch, 102.5ft (31.2m) drop (BLS), 30.3m drop (Trimble).

Bryn yr Ŵyn: summit to connecting bwlch with Bryn Llwyd, 42.5ft (13.0m) drop (BLS), 9.9m drop (Trimble).

I conducted the basic levelling survey in July 2000 and sent the details to Michael Dewey. Michael assessed the information and decided to include Bryn yr Ŵyn in his list to The 500-Metre Tops of England and Wales. The margin of uncertainly associated with the BLS method is within the error tolerance of the result, and I have wanted to re-visit and survey both hills and produce accurate absolute heights for each, ever since. Their heights as surveyed by the Trimble GeoXH 6000 appear below:

Bryn Llwyd 501.4m (converted to OSGM15) summit at SN 83574 92022 (average of four surveys conducted over two days)

Bryn yr Ŵyn 499.9m (converted to OSGM15) summit at SN 83919 92571 (average of five surveys conducted over two days)

Therefore the position of the relocated summit is at SN 83574 92022 and it consists of grass atop an ancient mound. The summit area and the hill itself has relatively easy underfoot conditions and consists of moor grass with a path leading from the critical bwlch to the south-west toward the connecting bwlch with Bryn yr Ŵyn.

This re-located summit position is not given a spot height on current Ordnance Survey maps and it is approximately 660 metres south south-westward from the previously listed summit position.

The full details for the hill are:

Cardinal Hill: Pumlumon Fawr

Summit Height: 501.4m (converted to OSGM15, and average of four summit surveys)

Name: Bryn Llwyd

OS 1:50,000 map: 135, 136

Summit Grid Reference (New Position): SN 83574 92022

Drop: 30.3m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Bryn Llwyd, with the summit of Bryn yr Ŵyn on the right and in the background of this photograph

For details on the 1^st Trimble survey and the 2nd Trimble survey that relocated the summit of this hill.

Myrddyn Phillips (May 2016)

Monday, 21 August 2017

Mapping Mountains – Summit Relocations – 500m Twmpau

No comments: