Mapping Mountains – Hill Reclassifications – The 500-Metre Tops of England and Wales – Deweys

Thack Moor (NY 611 462) – Dewey deletion

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Deweys and where I have had direct association with the status change.  These posts will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the Mountain tables book.

Thack Moor (NY 611 462)

The 500-Metre Tops of England and Wales are affectionately known after their hill list compiler; Michael Dewey.  This list mixes metric and imperial height in its criteria to bookend up to the 2000ft height band and takes in all hills in England, Isle of Man and Wales that are 500m and above and below 2000ft (609.6m) in height that have 30m minimum drop.

This list formed one of a number of lists that appeared in the Mountain tables book published by Constable in 1995 and at the time of publication comprised 373 hills with 164 in England, 5 in the Isle of Man and 204 in Wales.  The Deweys have undergone extensive revision since first publication with the initial stages forming the basis of this revision given below:

1995    Mountain tables published by Constable with 373 hills listed as Deweys.

April 2000    Strider (LDWA quarterly booklet) publishes contact details for David Purchase and Myrddyn Phillips who have found and list 24 and 14 possible new 500m tops respectively.

It was expanded versions of the above two lists that formed the basis of the next publication:

25^th May 2000    List of Possible 500 Metre Tops by Michael Dewey listing 44 hills.

David Purchase expands his Additional Dewey 500m Hills and Myrddyn Phillips produces lists of English 500m hills to measure and Welsh 500m hills to measure.

These lists formed the basis of the next publication:

29^th June 2000    Possible/Probable 500’s by Michael Dewey listing 77 hills.  Michael adopts following protocol; if one person proposes that a top should qualify as a 500 by personal survey, and is then confirmed by a second person, it should then be promoted to the main list.

April 2002    The 500+ Tops of England and Wales – The ‘New Deweys’ published in the Strider booklet and listing 66 new qualifying hills.

25^th May 2006    Rob Woodall republishes Michael’s main and possible/probable lists on the RHB Yahoo group file database. 

 

Mountain tables by Michael Dewey

The details for this deletion appear below:

The name the hill was listed by in the Deweys is Thack Moor, and it is adjoined to the Black Fell group of hills which are situated in the northern Pennines of England, and it is positioned with the A686 road to its south-east and the A689 road to its north-east, and has the small town of Alston towards the east and the small community of Renwick towards the south south-west.

This hill was included in the original 1995 Constable publication and listed with a 609m summit height which is adjoined to a triangulation pillar given the flush bracket height of 609.600m in the OS Trig Database, and which appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

As its 609m summit spot height was near the benchmark height of 2000ft (609.6m) it was prioritised for a GNSS survey and this took place on the 22^nd August 2012.  The summit of this hill was surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530 with two hours of data gathered, resulting in a summit height at the time of 609.645m.

The first Leica 530 survey of Thack Moor

As this result was so close to the benchmark height of 2000ft (609.6m) it was decided to re-visit and gather a further four hours of data.  The second survey was conducted on the 3^rd March 2013 by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica GS15, with Bob Smith editor of the Grough website joining us to write a feature on the survey, and by Aled Williams who also joined us on the summit.  The survey result at that time came to 609.625m which when converted using OSGM15 resulted in a summit height of 609.65m, which is higher than the maximum 2000ft (609.6m) height for Dewey status.

The second Leica GS15 survey of Thack Moor

These details were forwarded to the list author; Michael Dewey and the hill was deleted from his list in April 2013.

The full details for the hill are:

Name:  Thack Moor

OS 1:50,000 map:  86

OS 1:25,000 map:  31

Summit Height:  609.65m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SN 61166 46278 (Leica GS15)

Col Height:  c 549m (interpolation)

Col Grid Reference:  NY 63681 45681 (interpolation)

Drop:  c 61m (Leica GS15 summit and interpolated col)

Myrddyn Phillips (October 2020)

Mapping Mountains – Hill Reclassifications – Hewitts

Thack Moor (NY 611 462) – SubHewitt reclassified to Hewitt

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the English Hewitts (an acronym for Hill in England, Wales or Ireland over Two Thousand feet high).  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since first publication.

The listing of English Hewitts was published in booklet format by TACit Tables in June 1997 and entitled The Hewitts and Marilyns of England.  This list evolved out of The Absolute Summits of England and Wales which were known as the Sweats (an acronym for Summits in Wales and England Above Two-thousand FEET) and which was published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Hewitts and the preceding Sweats is Alan Dawson.

When the English Hewitts list was published in booklet format there were 178 qualifying hills listed with their criteria being any English hill at or above 2000ft (609.6m) in height with 30m minimum drop, accompanying the main list are two sub category’s entitled SubHewitts, with the two sets of criteria being any English hill at or above 600m and below 2000ft (609.6m) in height that have a minimum drop of 30m and any English hill at or above 2000ft (609.6m) in height with 20m or more and below 30m of drop.

The Hewtts and Marilyns of England by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Thack Moor (having previously been listed as Renwick Fell), and it is situated in the extended Cross Fell group of hills in the northern Pennines, and is positioned with the A686 road to its south-east and the A689 road to its north-east, and has the small town of Alston towards the east and the small community of Renwick towards the south south-west.

Thack Moor (NY 611 462)

Prior to this hill’s reclassification to Hewitt status it was listed as a SubHewitt with an estimated c 57m of drop based on the 609m summit spot height that appeared on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day and an estimated col height of c 552m.  

As its 609m summit spot height was near the benchmark height of 2000ft (609.6m) it was prioritised for a GNSS survey and this took place on the 22^nd August 2012.  The hill was surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530 and two hours of data were gathered, resulting in a summit height at that time of 609.645m.

Gathering data with the Leica 530 during the first summit survey of Thack Moor

As this result was so close to the benchmark height of 2000ft (609.6m) it was decided to re-visit and gather a further four hours of data.  The second survey was conducted on the 3^rd March 2013 by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica GS15, with Bob Smith editor of Grough joining us to write a feature on the survey, and by Aled Williams who also joined us on the summit.  The survey result at that time came to 609.625m which when converted using OSGM15 resulted in a summit height of 609.65m, which is higher than the minimum 2000ft (609.6m) height required for Hewitt status.

Gathering data with the Leica GS15 during the second summit survey of Thack Moor

The reclassification of this hill from Sub-Hewitt to Hewitt status was accepted by the list author and its new classification augmented in to the listing of the Hewitts in April 2013.

The full details for the hill are:

Name:  Thack Moor

OS 1:50,000 map:  86

OS 1:25,000 map:  31

Summit Height:  609.65m (converted to OSGM15)

Summit Grid Reference:  NY 61166 46278

Col Height:  552m

Col Grid Reference:  NY 636 456

Drop:  58m

Myrddyn Phillips (June 2019)

Prospective Ordnance Survey Datum Change and the effect on Mountain Heights

The Sunday Times have published a piece on the prospective reclassification to some of the hills in Britain if Ordnance Survey changed the height of their datum point based on current or future mean sea level. 

The Sunday Times article this morning

Mean sea level is regarded to have increased in height since the second geodetic levelling was completed by Ordnance Survey in 1921 and the third in 1956, both of which were based from measurements taken at Newlyn.

It is now accepted that sea levels are rising by around 1½ inches (4cm) per decade, and it is almost 100 years since the second geodetic levelling at Newlyn was completed, based on these simplified figures mean sea level would be approximately 40cm higher nowadays compared to the height of the current mean sea level datum point. 

If Ordnance Survey updated their datum point in a decade's time the height difference between the current point at Newlyn and an updated datum point would be approximately 40-45cm.  The hills that have been accurately surveyed by GPS/GNSS equipment that will be affected if Ordnance Survey alter their datum point, and therefore all known heights throughout Britain are reduced by 40-45cm appear below.

The Munros (Scotland, 3,000ft minimum height and above):

Beinn Teallach    914.6m summit height at NN 36139 85964.

 

The Leica set-up position on Beinn Teallach, sometimes it can get a wee bit windy on these Munros!

Corbetts (Scotland, 2,500ft and above and below 3,000ft in height with 500ft minimum drop):

Beinn na h-Uamha    762.4m summit height at NM 91719 66415.

Simms (Britain, 600m minimum height with 30m minimum drop):

Y Gribin    600.4m summit height at SH 84356 17712.

Foel Lwyd    600.1m summit height at SH 72040 72326.

Alan Dawson beside the Leica RX1250 at the summit of Y Gribin

Hewitts (England and Wales, 2,000ft minimum height with 30m minimum drop):

Nuttalls (Englland and Wales, 2,000ft Minimum height with 15m minimum drop):

Bloodybush Edge    609.8m summit height at NT 90223 14342.

Thack Moor    609.65m summit height at NY 61166 46278.

Calf Top    609.61m summit height at SD 66450 85624.

Tal y Fan    610.0m summit height at SH 72936 72648.

Mynydd Graig Goch    609.75m summit height at SH 49732 48518.

Thack Moor

Calf Top

Tal y Fan

Deweys (England, Wales and Isle of Man, 500m and above and below 609.6m (2,oooft) in height with 30m minimum drop):

Ffridd yr Allt Llwyd    500.4m summit height at SH 79724 29615.

Jo Barnard beside the Leica equipment on the summit of Ffridd yr Allt Llwyd

Y Pedwarau (Wales, 400m and above and below 500m in height with 30m minimum drop):

Craig y Dduallt    400.3m (converted to OSGM15) summit height at SJ 23280 40062.

Moel Tywysog    400.2m (converted to OSGM15)  summit height at SH 98480 65714.

Mynydd Deulyn    400.1m (converted to OSGM15) summit height at SH 75936 61265.

The summit of Moel Tywysog

 

The summit cairn atop Mynydd Deulyn

The above only take in a small percentage of the listings that have been compiled, and there are other listings that use a minimum height in their criteria, such as the Grahams and The Fours, but there are no hills that have been accurately surveyed with GPS/GNSS receiver within these listings that would be affected.  However, there are also a multitude of hills in all sorts of listings that are near to threshold minimum heights that have not yet been accurately surveyed by Differential GPS.  Therefore the overall changes within hill listings caused by a change and updating by Ordnance Survey of their datum point would be dramatic.

Myrddyn Phillips (October 2016)



The Times website

A related article published on The Guardian website

A related article published on The Telegraph website

A related article published on The Express website

A related article published on the WalesOnline website

A related article published on The Courier Mail website 

A related article published on The Daily Post website

A related article published on The Mail Online website