Showing posts with label Craig Stwlan. Show all posts
Showing posts with label Craig Stwlan. Show all posts

Tuesday, 28 March 2023

Mapping Mountains – Hill Reclassifications – 500m Twmpau


Craig Stwlan (SH 667 446) – 500m Sub-Twmpau addition

There has been an addition to the listing of the 500m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Aled Williams. 

The Trimble GeoXH 6000 gathering data at the summit of Craig Stwlan (SH 667 446) (Photo: Aled Williams)

The criteria for the list that this addition applies to are:

500m Twmpau - Welsh hills at or above 500m and below 600m in height with 30m minimum drop, with an accompanying sub list entitled the 500m Sub-Twmpau with the criteria for 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, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips and is available to download in Google Doc format from Mapping Mountains. 

The 500m Twmpau by Myrddyn Phillips

The name the hill is listed by is Craig Stwlan and it is adjoined to the Moelwyn Mawr 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 B4410 road to its south-west, the A487 road to its south and the A496 road to its east, and has the town of Blaenau Ffestiniog towards the east north-east.

When the list that became known as the 500m Twmpau was first compiled, this hill was listed with an estimated c 20m of drop, based on the 568m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 548m bwlch height, based on interpolation of 10m contouring between 540m – 550m. 

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

The hill was subsequently deleted from 500m Sub-Twmpau status due to initial LIDAR analysis, resulting in a 568.2m summit height and a 548.5m bwlch height, with these values giving this hill 19.7m of drop.  However, the hill has now been surveyed with the Trimble GeoXH 6000 and it is this result that is being prioritised.

Therefore, the addition of this hill to 500m Sub-Twmpau status is due to a Trimble GeoXH 6000 survey, resulting in a 568.4m summit height and a 548.3m bwlch height, with these values giving this hill 20.1m of drop, which is sufficient for it to be classified as a 500m Sub-Twmpau.

 

The full details for the hill are:

Group:  Moelwyn Mawr

Name:  Craig Stwlan

OS 1:50,000 map:  124

Summit Height:  568.4m (converted to OSGM15)

Summit Grid Reference:  SH 66736 44654

Bwlch Height:  548.3m (converted to OSGM15)

Bwlch Grid Reference:  SH 66693 44717

Drop:  20.1m

 

Myrddyn Phillips (March 2023)

 

 

 

 

 

  

Friday, 24 February 2023

Mapping Mountains – Trimble Surveys – Moelwyn Mawr


21.01.23  Craig Stwlan (SH 667 446), Craig Ysgafn (SH 659 443) and Pt. 524.3m (SH 661 457) 

I drove up the narrow road to Tanygrisiau with trepidation, but thankfully the gritters had kept it in good condition.  In front of me were snow-covered peaks, cliffs and boulders; while behind me were the distant profiles of other snow-clad mountains commanded by the bulk of Arenig Fawr in full winter splendour.  Having parked the car, the rigid frames of winter boots were reluctantly fitted to cold feet, with crampons and a walking axe strapped to my bag in preparation for any icy ground. 

Arenig Fawr (Photo: Aled Williams)

The plan was to visit the series of rocky tops to the east of Llyn Stwlan, before contouring around the lake to Bwlch Stwlan, whereupon a traverse of Craig Ysgafn would take me to the summit of Moelwyn Mawr.  Three surveys were fitted into the walk and the absence of a companion indicated that I would have my hands full when conducting these. 

View ahead from Clogwyn yr Oen (Photo: Aled Williams)

Having scrambled up to the summit of Clogwyn yr Oen, the view ahead looked beautiful but daunting.  The powder snow was deep in places and made progress difficult as I broke trail towards Ceseiliau Moelwyn.  The Welsh Highlands Sub-Top of Clogwyn y Bustach was visited, but not surveyed given that its status within the list is secure.  Ahead stood Craig Stwlan, which I had noted as a marginal P20, as such, I knew Myrddyn Phillips would appreciate having the hill surveyed, given that it was a candidate for his 500m Sub-Twmpau list.

Clogwyn y Bustach (Photo: Aled Williams)

The summit of Craig Stwlan was first to be surveyed.  This went quickly and efficiently, no doubt benefitting from the experience of recent surveys.  The views were stunning and I could discern the path that I would take to reach Bwlch Stwlan.  The bwlch of Craig Stwlan took a bit longer to locate.  This is often dictated by the flat topography of low points, but the winter conditions doubled the challenge of the task.  Once data had been collected, I ploughed onwards through the snow, thankfully joining a set of tracks that greatly eased progress. 

Trimble atop Craig Stwlan (Photo: Aled Williams)

I then joined the path known locally as Llwybr Gaseg.  This was spectacular in the conditions, perched above the freezing waters of Llyn Stwlan and the snow plastered slopes and gullies of Moelwyn Mawr and Craig Ysgafn above.  Care was needed in places, but no ice was met.  Upon reaching Bwlch Stwlan, a splendid view of Traeth Mawr and Porthmadog opened out. 

Along Llwybr Gaseg (Photo: Aled Williams)

Bwlch Stwlan (Photo: Aled Williams)

Craig Ysgafn looked imposing from Bwlch Stwlan, but the scarcity of ice made it an easier endeavour.  The south top was visited, another Sub-Top in the Welsh Highlands list, followed by the highest summit of the ridge.  However, the focus was the northern top, which classified a marginal P10 stood a chance of being promoted to the sub-list of The Welsh Highlands list that I co-author with Myrddyn Phillips. 

Craig Ysgafn (Photo: Aled Williams)

Summit of Craig Ysgafn looking toward Moelwyn Mawr (Photo: Aled Williams)

The bwlch of the north top was found to be a snug notch in the ridge, with an airy view down a gully that led straight down to the depths of Llyn Stwlan.  The survey was completed quickly and a short climb led to the summit of the north top.  A number of rocky protuberances competed for the highest point and so the Abney level was used to identify the correct outcrop.  Three men bypassed the summit as data collected, looking a little perplexed at the beeping noises emanating from the Trimble! 

Bwlch of the north top of Craig Ysgafn (Photo: Aled Williams)

Surveying the bwlch of the north top of Craig Ysgafn (Photo: Aled Williams)

Having collected data I made my way to the base of the upper slope of Moelwyn Mawr.  A determined plod progressively took me up to the steep slope, where a surprising amount of deep snow had settled. 

Climbing Moelwyn Mawr (Photo: Aled Williams)

Summit ridge of Moelwyn Mawr (Photo: Aled Williams)

The summit ridge of Moelwyn Mawr looked airy and alpine-like, with Yr Wyddfa and its neighbouring Eryri peaks looking majestic to the north.  Below was Llyn Croesor and Bwlch Rhosydd, between which was a hillock that I had recently identified as a potential Sub-Top for the Welsh Highlands list and as such, was the third surveying objective of the day. 

Summit of Moelwyn Mawr (Photo: Aled Williams)

Yr Wyddfa (Photo: Aled Williams)

The steep descent from the summit of Moelwyn Mawr was undertaken slowly and carefully.  I had been warned from a Blaenau Ffestiniog local whom I had met on the way up Moelwyn Mawr that the snow above Rhosydd was deep.  This warning was confirmed by the appearance of a partially buried stile and fence!  However, I was yet again fortunate to follow in the footsteps of others and so quick progress was made to the shores of Llyn Croesor. 

Deep snow (Photo: Aled Williams)

The final surveying objective (Photo: Aled Williams)

On the other side of the lake stood the craggy hillock that was to be surveyed, a short but enjoyable climb led to the summit, whereupon the Trimble was placed on the highest point of outcropping rock.  The scenery was breath-taking and I felt fortunate to be out in such a wild place.  However, the serenity would soon be broken by hard surveying work! 

Surveying the summit (Photo: Aled Williams)

The bwlch of the hill was unexpectedly complex.  I quickly realised that the gap had been plugged by a dam that formerly held the north side of Llyn Croesor when operating at reservoir capacity.  Furthermore, an outflow leat consisting of earth and large slabs of rock had been built on the northern side of the dam. 

The bwlch (Photo: Aled Williams)

The dam wall (Photo: Aled Williams)

Ironically, the ice axe strapped to my bag was finally unclipped and brought into use, with the adze helping to displace snow so that a better assessment of the terraformed bwlch could be made.  Two sets of data were gathered with the Trimble; one at the bottom of the dam wall and one above the leat at the spot where remaining natural ground was identified.  However, post survey, further analysis work revealed that the natural bwlch may well be extant to the north of the wall within the leat. 

The leat (Photo: Aled Williams)

Looking back at the final hill (Photo: Aled Williams)

Once the surveying equipment was packed away, a set of snow tracks sign-posted the way to Bwlch Rhosydd and ultimately the way back to civilisation.  Before I set off, a quick glance behind my shoulder revealed beautiful cloud formations above Moelwyn Mawr, brought in from the east and heralding a change in the weather.  It had been a great day out and one no doubt to be remembered for years to come.

Clouds above Moelwyn Mawr (Photo: Aled Williams)

Walkers ascending Moelwyn Mawr (Photo: Aled Williams)

 
Moelwyn Mawr clouds (Photo: Aled Williams)

Aled Williams (January 2023)

 

Survey Result: 

 

Craig Stwlan

Summit Height:  568.4m (converted to OSGM15)

Summit Grid Reference:  SH 66736 44654

Bwlch Height:  548.3m (converted to OSGM15)

Bwlch Grid Reference:  SH 66693 44717

Drop:  20.1m (500m Sub-Twmpau addition)

Dominance:  3.53%



Craig Ysgafn

Summit Height:  688.3m (converted to OSGM15)

Summit Grid Reference:  SH 65973 44394

Bwlch Height:  678.0m (converted to OSGM15)

Bwlch Grid Reference:  SH 65960 44382

Drop:  10.3m (Welsh Highland Sub addition)

Dominance:  1.49%



Pt. 524.3m

Summit Height:  524.3m (converted to OSGM15)

Summit Grid Reference:  SH 66117 45783

Bwlch Height:  513.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 66131 45774

Drop:  10.7m (Welsh Highland Sub addition)

Dominance:  2.05%


 

For further details please consult the Trimble Survey Spreadsheet

 

 

  

Friday, 19 May 2017

Mapping Mountains – Hill Reclassifications – 500m Twmpau



THIS HILL HAS SUBSEQUENTLY BEEN REINSTATED TO 500m SUB-TWMPAU STATUS


Craig Stwlan (SH 667 446) – 500m Sub-Twmpau deletion

There has been a deletion to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The Twmpau is the title for the list of Welsh P30s and takes in all Welsh hills that have a minimum 30m of drop, with this deletion affecting the 500m height band of hills within the Twmpau.

Accompanying the main list of Twmpau hills is a sub category list of hills, with the criteria for this sub list in the 500m height band of hills being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop.  Details to this height band of the Twmpau were published on the Mapping Mountains site on 15th June 2015.

Prior to analysis of LIDAR data the hill had been listed with c 20m of drop based on the 568m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 548m based on interpolation of bwlch contouring between 540m – 550m.

The hill is situated in the Moelwynion group of hills with its Cardinal Hill being Moelwyn Mawr (SH 658 448) and is placed in the Region of North Wales (Region A, Sub-Region A1).  The hill is situated with the town of Blaenau Ffestiniog to the east north-east and the small village of Croesor to the west.

If wanting to visit the hill it can be easily accessed from the east north-east from the end of the paved public road which is situated above the small community of Tanygrisiau, beyond a locked gate the paved road continues up toward the reservoir of Llyn Stwlan, and Craig Stwlan is positioned just above the north-eastern part of this lake.

The name of the hill is Craig Stwlan and its deletion from 500m Sub-Twmpau status is due to the analysis of LIDAR data by Aled Williams.  LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

Aled’s analysis of LIDAR data gives the hill the following details:


Craig Stwlan

Summit Height:  568.2m

Summit Grid Reference:  SH 66735 44655

Bwlch Height:  548.5m

Bwlch Grid Reference:  SH 66693 44715

Drop:  19.7m


Therefore, the 568.2m LIDAR data produced for the summit position at SH 66735 44655 and the 548.5m LIDAR data produced for the bwlch position at SH 66693 44715 gives this hill 19.7m of drop which is insufficient for it to retain its status as a 500m Sub-Twmpau.


The full details for the hill are:

Cardinal Hill:  Moelwyn Mawr

Summit Height:  568.2m (LIDAR data)

Name:  Craig Stwlan

OS 1:50,000 map:  124

Summit Grid Reference:  SH 66735 44655

Drop:  19.7m (LIDAR data)


The overall total for the 500m Twmpau remains at 225 hills with the overall total for the 500m Sub-Twmpau decreasing by one to 96 hills.  The list of the 500m Twmpau was published on 15th June 2015 with all subsequent changes having been detailed on Mapping Mountains


My thanks to Aled Williams for sending the details of this hill to me.

Myrddyn Phillips (May 2017)