Showing posts with label Mynydd Nodol. Show all posts
Showing posts with label Mynydd Nodol. Show all posts

Sunday, 16 August 2026

Mapping Mountains – Significant Height Revisions – The 500-Metre Tops of England and Wales – Deweys


Mynydd Nodol (SH 865 393) 

There has been a Significant Height Revision to a hill that is listed in the The 500-Metre Tops of England and Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 summit survey conducted by Myrddyn Phillips and LIDAR bwlch analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

Mynydd Nodol (SH 865 393)

The criteria for the list that this height revision applies to are:

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. 

Mountain tables by Michael Dewey

Michael Dewey died on the 5th November 2022.  His wife; Gillian wished for this list to be carried on and made provision for it to be co-authored by Myrddyn Phillips.  Michael will always be the compiler and originator, it’s just that he’s now got a co-author to safeguard and carry this list on.

The name the hill is listed by is Mynydd Nodol and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales, and it is positioned with Llyn Celyn and the A4212 road to its north and a minor road to its south, and has the town of Y Bala towards the south-east.

When the original list of Deweys appeared in the Mountain tables book published by Constable in 1995, this hill was listed with a non-interpolated summit height of 530+m, based on the uppermost 530m ring contour that appeared on the contemporary 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 Trimble GeoXH 6000 and 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. 

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Nodol (SH 865 393)

The survey with the Trimble GeoXH 6000 gives the summit of this hill as 540.0m positioned at SH 86514 39339, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or other GNSS equipment or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 540.0m and this was derived from a Trimble GeoXH 6000 survey, this is 10.0m higher than the originally listed summit height of 530+m, which was based on the non-interpolated uppermost 530m ring contour that appeared on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and 1m height than the 539m summit spot height that now appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and importantly this height signifies that an uppermost 540m ring contour is missing from these maps. 

 

The full details for the hill are:

Group:  Arenig Fawr

Name:  Mynydd Nodol

OS 1:50,000 map:  124, 125

Summit Height (New Height):  540.0m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 86514 39339 (Trimble GeoXH 6000)  

Bwlch Height:  370.8m (LIDAR)

Bwlch Grid Reference:  SH 85660 39014 (LIDAR)

Drop:  169.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (August 2026)

  

Saturday, 4 July 2026

Mapping Mountains – Significant Height Revisions – 500m Twmpau and The Welsh Highlands – Uchafion Cymru

 

Mynydd Nodol (SH 865 393) 

There has been a Significant Height Revision that is retrospective 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 a Trimble GeoXH 6000 summit survey conducted by Myrddyn Phillips and LIDAR bwlch analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

Mynydd Nodol (SH 865 393)

The criteria for the two listings that this height revision 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

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.

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

The name the hill is listed by is Mynydd Nodol and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with Llyn Celyn and the A4212 road to its north and a minor road to its south, and has the town of Y Bala towards the south-east.

When the listings of the 500m Twmpau and The Welsh Highlands – Uchafion Cymru were first compiled, this hill was listed with a summit height of 539m, based on the spot height 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 Trimble GeoXH 6000 and 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. 

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Nodol

The survey with the Trimble GeoXH 6000 gives the summit of this hill as 540.0m positioned at SH 86514 39339, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or other GNSS equipment or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 540.0m and this was derived from a Trimble GeoXH 6000 survey, this is 1.0m higher than the originally listed summit height of 539m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and importantly this height signifies that an uppermost 540m ring contour is missing from this map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Arenig Fawr

Name:  Mynydd Nodol

OS 1:50,000 map:  124, 125

Summit Height (New Height):  540.0m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 86514 39339 (Trimble GeoXH 6000)  

Bwlch Height:  370.8m (LIDAR)

Bwlch Grid Reference:  SH 85660 39014 (LIDAR)

Drop:  169.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips and Aled Williams (July 2026)

Monday, 11 April 2022

Mapping Mountains – Trimble Surveys – Arenig Fawr

 

25.02.22  Mynydd Nodol (SH 865 393) 

Mynydd Nodol (SH 865 393)

Having visited and surveyed Moel Heulog (SH 987 353) I wanted a relatively easy hill to visit before continuing my way toward Nantlle for the weekend with my brother, and Mynydd Nodol ticked all boxes, especially as it is over 500m and qualifies for Dewey status and I had only visited its heathery domain once before, in April 2000 when I remained on its summit for 10-15 minutes admiring the extensive view. 

Time between ascents, and especially ones encompassing 22 years have a tendency to create paths on hills where few previously existed.  These intervening years have also created online logs giving detail of various routes to the summit of this particular hill.  My previous route followed a fence line and I found going on its north easier than beside it on its south, picking up a narrow animal track that took me toward the upper section of the hill.  However, I remember the going was rough in places.  One online log mentioned a path to the south of this fence and as a convenient parking spot close to the start of a track gave access to this fence, this was my chosen route of ascent for the day. 

Leaving my car I joined the track heading directly northward across the western flank of Mynydd Nodol.  The sun cast colour across the land with shadowed patches accentuating the darkened heather, of which there was plenty. 

Mynydd Nodol from the track leading to the disused tip

The track led past a disused tip and proceeded to lose a little height before connecting with the fence line that then strode confidently upward toward the summit.  I left the track at its high point having spotted what I thought a sheep track through the heather, this meandered uphill as a path, always on the south of the fence which was about 20-30 metres away.  The path gave relatively easy progress uphill and only petered out toward the top. 

Arenig Fach and Llyn Celyn

As I headed up I could see an aerial positioned on the summit and suspected it had been set up by a SOTA enthusiast, as I neared the point where the fence joins the summit ridge the person who had set it up was heading my way, we stopped and chatted for ten minutes or so.  He had already been to the top of Arenig Fach earlier in the day and wanted to visit the summit of Carnedd y Filiast before nightfall, my humble two little hill surveying day felt inadequate by comparison! 

Arenig Fawr

I watched him start to descend toward the path I had used on my ascent before I headed across to the ridge path and the large cairn that marks the summit of this hill.  It felt good to be back, but with a gap of 22 years since my only visit I suspect it will be the last time I venture to this particular hill.  Over the intervening years I had passed Mynydd Nodol an inordinate amount of times travelling west and heading back east on the A4212 road beside Llyn Celyn.  When visibility permitted I would always have a quick glance toward the top of Mynydd Nodol and wonder when my next visit would be.  One hill after another always, until today, got in the way, as they are prone to do. 

The 22 year wait for my second visit did not disappoint as the view from the summit was as I remembered; extensive, and although on my previous visit I had spent a number of minutes looking out toward the many hills that are on view, my priority today was to establish the high point of the hill and survey it.  LIDAR gives two options for the summit, both close to one another, with a further point nearer the fence only just lower.  With reports of Abney level surveys on the Hill Bagging website giving a rock beside the large summit cairn as 20cm higher than the point beside the fence.  I assessed the lay of land from a number of directions and came to the same conclusion that the rock beside the cairn was the highest point of the hill. 

LIDAR image of Mynydd Nodol (SH 865 393)

As a brisk breeze blew across the upper part of the hill I secured my rucksack in place with two substantial rocks, one on either side, before placing the Trimble on top aligned with the high point of the rock below, before noting the measurement offset between its internal antenna and the rock at its base.  It only took a couple of minutes for the equipment to attain the 0.1m accuracy level before data should be logged and it was soon then activated to gather data. 

During data collection I stood behind the large cairn out of view of the equipment and let it gather its customary five minutes of data.  Once data were gathered and stored I closed the equipment down, took a few photographs and packed it away. 

Gathering data at the summit of Mynydd Nodol

Leaving the summit I looked back to it as I re-joined the ridge path, after all this would probably be my last visit to this hill.  This feeling of finality has only just entered my conscience; it is due to age and the realisation of time between ascents, it is also the realisation of however many hills there are in Wales, there are always new ones to prioritise and visit. 

I met and chatted with a couple on my way down, the man originated from Aberystwyth and the woman from Cardiff.  They had lived in Y Bala for eight years, so Mynydd Nodol is one of their local hills.  They were on the initial part of the path as it leaves the track.  I waved my goodbyes after ten minutes or so and made my way down to the track, as I did so I peered up and the blue sky from earlier in the day had now been replaced with high cloud giving a late afternoon feel to proceedings. 

 

Survey Result: 

 

Mynydd Nodol

Summit Height:  540.0m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision) (Deweys significant height revision)

Summit Grid Reference:  SH 86514 39339 (Trimble GeoXH 6000)

Bwlch Height:  370.8m (LIDAR)

Bwlch Grid Reference:  SH 85660 39014 (LIDAR)

Drop:  169.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  31.34% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For further details please consult the Trimble Survey Spreadsheet