Mapping Mountains – Hill Reclassifications – 100m Twmpau

Maes Glas Mawr (SH 768 724) – 100m Twmpau reclassified to 100m Sub-Twmpau

There has been a reclassification to a hill that is listed in the 100m Twmpau, with the summit height, its location, the drop and status of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000, both conducted by Myrddyn Phillips with the latter taking place on the 10^th October 2018.

Maes Glas Mawr (SH 768 724)

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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 name of the bounded land where the summit of this hill is situated is Maes Glas Mawr, and this was derived from local enquiry and it is the name that this hill is now listed by, and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is encircled by minor roads with the B5106 road and the Afon Conwy (River Conwy) to its east, and has the town of Conwy towards its north.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list as its summit was thought to be higher than its adjacent and southerly hill known as Clytiau Poethion which is positioned at SH 76337 71799, both hills have now been surveyed with Clytiau Poethion confirmed as the higher resulting in the reclassification of Maes Glas Mawr.

When this list was standardised and interpolated heights and drop values also included Maes Glas Mawr was listed with an estimated c 39m of drop based on the 107m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and an estimated bwlch height of c 68m based on interpolation of 10m bwlch contouring between 60m – 70m.

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

These values were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and entitled the Interactive Coverage Map became available online, and the listed drop value remained the same.

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. 

LIDAR image of Maes Glas Mawr

Importantly LIDAR analysis gave Clytiau Poethion (SH 76337 71799) as higher than Maes Glas Mawr and this has subsequently been confirmed by a Trimble GeoXH 6000 survey, therefore the bylchau for each hill is swapped as are their classifications, resulting in a Trimble GeoXH 6000 summit height for Maes Glas Mawr of 108.5m positioned at SH 76876 72414, and a bwlch height of 87.05m produced by LIDAR analysis and positioned at SH 76604 71933, with these values giving this hill 21.4m of drop, which is sufficient for this hill to be reclassified to 100m Sub-Twmpau status.

The full details for the hill are:

Group:  Carneddau

Name:  Maes Glas Mawr

OS 1:50,000 map:  115

Summit Height:  108.5m (converted to OSGM15)

Summit Grid Reference:  SH 76876 72414

Bwlch Height:  87.05m (LIDAR)

Bwlch Grid Reference:  SH 76604 71933 (LIDAR)

Drop:  21.4m (LIDAR)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)

Mapping Mountains – Significant Name Changes – 100m Twmpau

Maes Glas Mawr (SH 768 724)

There has been a Significant Name Change to a hill that is listed in the 100m Twmpau, with the summit height, its location, the drop and status of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 10^th October 2018.

Maes Glas Mawr (SH 768 724)

The criteria for the list that this name change applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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 hill is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is encircled by minor roads with the B5106 road and the Afon Conwy (River Conwy) to its east, and has the town of Conwy towards its north.

The hill originally appeared in the 100m P30 list on Geoff Crowder’s v-g.me website under the partly invented and transposed name of Bryn Glyn Uchaf with an accompanying note stating; Name from buildings to the South-West.

 

Bryn Glyn Uchaf

107m

SH769725

115

17

Height from 1989 1:50000 map. Name from buildings to the South-West

During my early hill listing I thought it appropriate to either invent a name for a hill, or use a name that appeared near to the summit of the hill on Ordnance Survey maps of the day.  My preference was to use farm names and put Pen, Bryn or Moel in front of them.  This is not a practice that I now advocate as with time and inclination place-name data can be improved either by asking local people or by examining historic documents, through this form of research an appropriate name for the hill can usually be found.

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

After visiting this hill I called at Glyn Uchaf farm and followed instructions pinned on the front door to call at the new house, which is situated just down the track from Glyn Uchaf.  Having knocked on the front door of the new house, Tomi Owen opened it and immediately invited me in and offered me a drink and a bite to eat.  I sat at the table with my rucksack on the kitchen floor whilst Tomi offered me a cup of tea and a refreshing cold drink of orange, during which I happily indulged in a plate full of shortbread.  Having explained where I’d been and my interest in upland place-names Tomi told me that he’d lived at Glyn Uchaf since 1947 and is now aged 76 and that the hill is on his land and although it has no individual name the upper field where the summit is situated is known as Maes Glas Mawr.

Tomi Owen of Glyn Uchaf farm

Therefore, the name this hill is now listed by in the 100m Twmpau is Maes Glas Mawr, and this was derived from local enquiry.

The full details for the hill are:

Group:  Carneddau

Name:  Maes Glas Mawr

Previously Listed Name:  Bryn Glyn Uchaf 

OS 1:50,000 map:  115

Summit Height:  108.5m (converted to OSGM15)

Summit Grid Reference:  SH 76876 72414

Bwlch Height:  87.05m (LIDAR)

Bwlch Grid Reference:  SH 76604 71933 (LIDAR) 

Drop:  21.4m (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)

Mapping Mountains – Trimble Surveys – Carnedd Llywelyn

10.10.18  Maes Glas Mawr (SH 768 724) and Clytiau Poethion (SH 763 717)  

Maes Glas Mawr (SH 768 724)

Having analysed these two hills with LIDAR I knew before visiting that in all likelihood the subsequent Trimble survey would confirm the summit relocation of Maes Glas Mawr to Clytiau Poethion, with the former becoming a Sub-Twmpau and the latter a new P30.  However, there were reports on the Hill Bagging website that both summits were plagued with gorse, and as I (and the Trimble) do not like gorse it was conjecture if summit data from either hill could be gathered.

LIDAR image of Maes Glas Mawr and Clytiau Poethion

As I parked on the outskirts of the small community of Tyn-y-groes the morning’s sunshine was now turning unseasonably warm with blue skies radiating down and hardly a patch of cloud in the sky.

A public footpath led north-west from the western fringes of Tyn-y-groes toward the summit of Maes Glas Mawr and once I’d done battle with a barb wired fence resulting in another battle scar, this time a bloodied finger, I plodded up toward its summit.

The summit of this hill consists of a steep north-westerly side with the upper part covered in high gorse.  Thankfully the highest point was on the edge of the gorse looking down over the steep flank of the hill, this at least gave a semblance of chance for gathering data.

Implanted in to the summit were the remains of a gnarled gorse bush and by wedging my rucksack in to its wooded lower part and placing the Trimble on top, it gave it elevation above its immediate surrounds, and a relatively secure position to balance atop for the allotted data collection.

The Trimble set-up position at the summit of Maes Glas Mawr

As it beeped away gathering its individual datum points I sat amongst the gorse on a small patch of grass and luxuriated in a restful few minutes bathed in morning sunshine.

Gathering data at the summit of Maes Glas Mawr

Once data were gathered and stored I walked the short distance down to Glyn Uchaf farm where I hoped to make place-name enquiries for the hill.  A note pinned to the door gave instructions to call at the ‘new house’ if there was no reply at the farm.  I proceeded down the track to the new house and knocked on the door, Tomi Owen answered and without a moment’s hesitation invited me in.  Within a few minutes Tomi was offering me a cup of tea, or cold drink and some shortbread.  I spent about 20 minutes with Tomi and he proved a delight to speak with, telling me that the upper field where the summit of this hill is situated is known as Maes Glas Mawr.

A nice way to spend a part of a hill walk

Tomi Owen

Having finished my drink and eaten my shortbread I thanked Tomi for his hospitality and headed down the continuation of the track to a minor road and a footpath through Craflwyn wood, this brought me down to another minor road and a walk up it to try and gain access to the field leading toward the gorse laden summit of Clytiau Poethion.

By now it was beginning to get quite warm and the thought of gorse bashing in shorts and a short sleeved top did not enthuse me, however it needed to be done and my first venture in to the prickly stuff unearthed a rather exotic looking plant.  This is the first time I’d seem such a plant on a Welsh hill, although I suspect there are many more dotted around the landscape.

An exotic looking plant on Clytiau Poethion

Deciding that the summit was not by this spot I backtracked out of the gorse and tried another spot, this again was not the summit, I backtracked and tried a different angled approach but within a few metres I again backtracked.  Fourth time lucky I thought, and this time I followed the grass at the periphery of the gorse to its high point and tried to find a relatively easy way in to the prickly stuff.

The easiest option seemed to be to head toward a prominent telegraph pole and work my way up the ridge toward its high point, I was at last making progress and using the Trimble as a hand-help device I zeroed in to the summit position.  When found it proved to be amongst a mass of very high gorse, I wondered what to do.  Not to be outdone I wondered if I could balance the Trimble on a gorse branch and gather data from this elevated position, and as said branch was positioned over what I judged to be the high point of the hill, it proved a relatively easy way to overcome the difficulty.

The Trimble set-up position at the summit of Clytiau Poethion

As the Trimble gathered ten minutes of data I sat below it, looking up toward it as it balanced precariously like a meerkat standing bolt upright on a slender elevated branch.  I wondered what the data set would be like once processed, but as I seldom carry the 2m pole this unusual surveying position would have to do.

Gathering data at the summit of Clytiau Poethion

The Trimble survived its adventure and once packed away I found an easy way out of the gorse leading me down on a public footpath toward the renovated farm house of Clytiau Poethion.  The land where the summit of this hill is situated is named on the Tithe map as a part of this farm’s land; and not surprisingly the Tithe names this land after that of the farm; Clytiau Poethion.

Looking back toward the summit of Clytiau Poethion

It was only a short walk from here following the minor road to where my car was parked.  My next objective was to visit and survey three hills and attempt to determine which is higher, this is something I’ve wanted to do ever since first listing them many a year ago; Bryn Eithin (SH 775 752), Bwlch Mawr (SH 777 755) and Cae Alen (SH 781 758).

Survey Result:

Maes Glas Mawr (significant name change)

Summit Height:  108.5m (converted to OSGM15) (confirmed as lower than Clytiau Poethion)

Summit Grid Reference:  SH 76876 72414

Bwlch Height:  87.05m (LIDAR)

Bwlch Grid Reference:  SH 76604 71933 (LIDAR)

Drop:  21.4m (Trimble summit and LIDAR bwlch) (100m Twmpau reclassified to 100m Sub-Twmpau)

Dominance:  19.76% (Trimble summit and LIDAR bwlch)

Clytiau Poethion (significant name change)

Summit Height:  109.1m (converted to OSGM15) (confirmed as higher than Maes Glas Mawr)

Summit Grid Reference:  SH 76337 71799 (summit relocation confirmed)

Bwlch Height:  68.7m (LIDAR)

Bwlch Grid Reference:  SH 77496 72493 (LIDAR)

Drop:  40.35m (Trimble summit and LIDAR bwlch) (100m Twmpau addition)

Dominance:  37.00% (Trimble summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet