Mapping Mountains – Significant Height Revisions – Y Pellennig

Ynys Arw (SH 266 945) 

There has been a Significant Height Revision to a hill that is listed in the Y Pellennig - The Remotest Hills of Wales which was initiated by a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on the 13^th September 2015.

The criteria for this list appear below:

Y Pellennig –The Remotest Hills of Wales comprise all Welsh hills whose summit is 2.5km or more from the nearest paved public road and which have a minimum 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams.

The name of the hill is Ynys Arw and it forms one of the islands that make up the archipelago of Ynysoedd y Moelrhoniaid (The Skerries), these islands are positioned to the north-west of Ynys Môn (Anglesey). 

Ynys Arw is the most south-westerly island of this archipelago and has two high points, with the more southerly of these being the highest.  As Ynys Arw is a tidal island it is connected to its higher neighbour at high tide, the higher island is where The Skerries Lighthouse is situated and is the highest point of the archipelago and is also listed as a Pellennig hill.

The survey of this hill was suggested by Rob Woodall and it was conducted late in the afternoon.  Twelve of us visited Ynysoedd y Moelrhoniaid in a Rib using a company named RibRide who are based at the Holyhead Marina during the summer months, and the trip cost £35.00 per person.

The summit of Ynys Arw is easily accessed at low tide from the Lighthouse, although hands on rock are required to get down to the wet land between it and the higher island.  This connecting land is cut off from the higher island at high tide.  The ascent from the connecting land is initially over wet rock and then grass which has a multitude of burrowed Tern nests excavated into it.

The island of Ynys Arw was not classified in any list prior to the survey with the Trimble GeoXH 6000 as it is given an uppermost contour of only 10m on Ordnance Survey 1:25,000 Explorer maps.  It was surveyed with the Trimble GeoXH 6000 at being 15.2m (converted to OSGM15) high.

The 15.2m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is not a dramatic height revision when compared to an estimated c 12m height for this island’s summit based on contour interpolation taken from its uppermost 10m map ring contour, but as the contours on the Ordnance Survey 1:25,000 Explorer map are at 5m intervals it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the surveyed height produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

Therefore this hill’s new summit height is 15.2m (converted to OSGM15) which is 3.2m higher than the previously estimated height and 5.2m higher than its uppermost ring contour on Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Island:  Ynysoedd y Moelrhoniaid

Summit Height (New Height):  15.2m (converted to OSGM15, Trimble GeoXH 6000)

Name:  Ynys Arw

OS 1:50,000 map:  114

Summit Grid Reference:  SH 26647 94598 (Trimble GeoXH 6000)

Drop:  15.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Gathering data from the summit of Ynys Arw which resulted in this island's significant height revision

For details on the survey that significantly revised the summit height of this hill

© Crown: CHERISH PROJECT 2019. Produced with EU funds through the Ireland Wales Co-operation Programme 2014-2020. All material made freely available through the Open Government Licence.

Myrddyn Phillips and Aled Williams (October 2015)

Mapping Mountains – Hill Reclassifications – Y Pellennig – The Remotest Hills of Wales

Ynys Arw (SH 266 945) - Pellennig addition 

There has been a new hill that has entered the list of Y Pellennig – The Remotest Hills of Wales, due to a recent Trimble survey.  The hill is situated on Ynysoedd y Moelrhoniaid, this small group of islands are positioned to the north-west, off the north-west coast of Ynys Môn; its name is Ynys Arw.

Ynys Arw (SH 266 945) is the most south-westerly island of this archipelago and has two high points, with the more southerly of these being the highest.  Ynys Arw is tidal and is connected by land to its higher neighbour at low tide, the higher island is where The Skerries Lighthouse is situated and is the highest point of the archipelago and is also listed as a Pellennig hill.

The summit of Ynys Arw is easily accessed at low tide from the Lighthouse, although hands on rock are required to get down to the connecting land that is submerged at high tide.  The ascent from this wet sea weeded land is on rock and then grass that has a multitude of burrowed Tern nests excavated into it.

The high point of Ynys Arw has a 10m ring contour on it and no spot height on current Ordnance Survey maps, it was surveyed with the Trimble GeoXH 6000 at being 15.2m (converted to OSGM15) high, and as the criteria for qualification to the Pellennig list is a hill whose summit is a minimum of 2.5 km from the nearest paved public road and which has a minimum drop of 15m, this hill easily qualifies on the distance criterion and now meets the necessary minimum drop criterion to become the latest entry to the Pellennig list.

This now brings the overall total for Y Pellennig to 168 hills for the Complete list (All Wales), with the total for the Mainland Wales list remaining the same at 124 hills.  The Master List will be duly updated on the Mapping Mountains site.

The full details for the hill are:

Cardinal Island:  Ynysoedd y Moelrhoniaid

Summit Height:  15.2m (converted to OSGM15, Trimble GeoXH 6000)

Name:  Ynys Arw

OS 1:50,000 map:  114

Summit Grid Reference:  SH 26647 94598 (Trimble GeoXH 6000)

Drop:  15.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

The list of additions in the Y Pellennig list since the 1^st edition of Y Pellennig – The Remotest ills of wales of Wales was published by Europeaklist is as follows:

ADDITIONS

Pen Diban (SH 112 205)

Ynys Arw (SH 266 945)

Ynys Arw (SH 266 945) - the new Pellennig hill

For details on the survey that promoted this hill to Pellennig status please click {here}

© Crown: CHERISH PROJECT 2019. Produced with EU funds through the Ireland Wales Co-operation Programme 2014-2020. All material made freely available through the Open Government Licence.

Myrddyn Phillips and Aled Williams (September 2015)

Mapping Mountains – Trimble Surveys – Mynydd Twr

13.09.15  Ynysoedd y Moelrhoniaid (SH 267 947) and Ynys Arw (SH 266 945)   

Ynysoedd y Moelrhoniaid (SH 267 947)

The islets of Ynysoedd y Moelrhoniaid lie like a rough pearled necklace, wave battered 3 kilometres (1.9 miles) off the north-west coast of Ynys Môn.  They form a compact archipelago oriented north-east to south-west and stare back on their much larger island neighbour.  Perched on their highest point is The Skerries Lighthouse, with the word Skerry deriving from the Old Norse ‘sker,’ which means a small rocky reef or island, with the Welsh name for the islands translating as ‘the islands of Bald-headed Grey Seals’.

Our visit to these islands was organised by Adrian Rayner via Rib Ride, who are based in Holyhead and run a variety of trips around the north-west coast of Ynys Môn.  We met at Holyhead Marina and congregated in the café and waited for Adrian’s arrival.  There were 12 booked for this trip; George Morl, Alan Holmes, Alex Cameron, Douglas Law, Bob Kerr, Sarah Kerr, Tony Jenkins, Rob Woodall, Sheila Glew, John Glew, Adrian Rayner and me, also with us was Gordon Adshead who had come to see us off.

(L-R) Alex, Gordon, Adrian, John, Sheila, George, Tony, Alan, Sarah, Bob, Doug, Charles (skipper) and Rob

Charles; our skipper for the day

Once the formalities had been conducted beside the RIB we climbed aboard for a rather luxuriant passage out to sea.  The RIB used for this trip was once owned by Bear Grylls and his name and image is still used in Rib Ride’s promotional material.  The RIB was rather plush with a central cabin which had fold out canopied sides to use when the weather was rough, and an option for seated or standing position behind the controls and which was protected by a Perspex screen.  Behind this was a seat long enough for five people and in front was seating for five or six people.

At the front of the RIB

And at the back of the RIB.  Photo: RibRide

The forecast for the afternoon was good, and we had been lucky as no more than two days prior to today it was predicted that rain was going to envelop this part of the country for the whole afternoon.  As we pulled out from Holyhead the sky cast out colour and the sea was becalmed.  Beyond the harbour breakwater there was a light swell as we proceeded across the straight between Ynys Môn and Ynysoedd y Moelrhoniaid, but conditions proved relatively calm.

It’s a wonderful experience nearing an island, watching as it forever gets larger on the horizon, and today it was the islands Lighthouse that dominated the view as it stood firmly in place attached on the highest part of the archipelago with its white coloured exterior set against the backdrop of a sun drenched grey sky. 

The Skerries Lighthouse

The RIB slowly rounded the western side of the islands and was manoeuvred into the small bay below the Lighthouse.  This entrance was magical as we were suddenly transported in to a different world full of lazy seals whooping their guttural calls and an assortment of small, delightful islets, all ready for us to explore.

Seals relaxing in the afternoon sun

Once the RIB had been secured onto the iron barred ladder leading vertically up the sides of rock we clambered up and started our exploration of the islands.  It seems that there is a need to head toward the high point of any hill or island and today was no exception.  The path leading up to the Lighthouse led through a beautiful array of white daisies, all looking up with their colour mixed in their green rooted grass, set against the white of the Lighthouse they resembled a mountain meadow in spring.

Bob, followed by Alan, climbing up the ladder onto the island

Bob and Sarah with The Skerries Lighthouse in the background

The carpet of flowers

As I walked around the Lighthhouse the ground dropped steeply away to the east and the coastline of Ynys Môn gleamed back in its hazy afternoon light.  There were two potential summit points, one on the southern side of the Lighthouse and the other on the western side.  There was consensus between myself, Alan and one or two others that the highest point was on the southern side, this high point consisted of a rock that was positioned just under the base of the walkway which encircled much of the eastern and southern side of the Lighthouse, however the highest rock was pinned in with buildings either side of it, this had potential to disrupt satellite coverage, and as I set the Trimble up with its internal antenna aligned to the high point of what remains of the natural rock I thought it would take a long time for the 0.1m accuracy level to be attained before logging should start.  Remarkably this accuracy level was attained within a couple of minutes and I quickly pressed ‘Log’ and hid behind a rock, we’ll have to see what the processed data is like and whether the data set is good or has been compromised by the position of the Trimble.

Gathering data at the summit of Ynysoedd y Moelrhoniaid

Charles and Alan look on with the Trimble positioned on the highest natural rock that still exists on Ynysoedd y Moelrhoniaid

Once summit data were collected I headed to the western side of the Lighthouse wanting to gather another five minute data set from the other potential summit position, this was straight under the side of the Lighthouse and after waiting ten minutes the accuracy level was only down to 0.19m, and whilst waiting I looked out on everyone exploring the other islets, so I decided to switch the Trimble off and start doing likewise.

The Trimble positioned on the high point on the western side of the Lighthouse

The highest islet where the Lighthouse is situated has another islet to its south-west named Ynys Arw; this has two main high points, with the southerly of these being the highest.  There were already a number of people scampering all over these high points and I headed over to join them.  This south-westerly islet is cut off from the others at high tide but the pebbles and seaweed of relatively dry land had been exposed as low tide enabled us to visit farther afield from the main islet.

Sarah, Alex and Rob (on left of photo) on the adjacent high point to the Lighthouse with the summit of Ynys Arw on the right of photo

Alex and Rob heading over to Ynys Arw

Sarah below the Lighthouse, with its lower rocks on the right of this photo

John helped me find the scramble down a rock shelf onto the connecting land between the islets and I soon joined Adrian, Rob and Alex on the high point.  Adrian and Alex soon headed off and I remained with Rob for a few minutes talking about the Welsh Remotest list and Alan’s Sibs list, with the furthest northerly island which is named Ynys Berchen, being listed within each as a Pellennig and a Sub-Sib, Rob asked the criteria for the Pellennig list and wondered whether the small islet we were on would meet the minimum drop of 15m.  As he headed off toward the northerly Pellennig / Sub-Sib I set the Trimble up and gathered another five minutes of data from the high point of the southerly islet.

Alex scrambling back up the rock on his way past the Lighthouse toward Ynys Berchen

The Skerries Lighthouse from the summit of Ynys Arw

Ynysoedd y Moelrhoniaid bathed in sunshine

The northerly island of Ynys Berchen which is listed as a Pellennig and Sub-Sib

As the Trimble did its stuff I happily stared out on this stunningly beautiful place, content to be on my own soaking up its ambience.  By this time a few people were gathering, waiting to descend toward the RIB, and once the five minutes of allotted data were collected, I took a few photos with the Lighthouse shining white as a slight breeze blew in from the sea.

Gathering data from the summit of Ynys Arw

As I slowly made my way down the wet rock back onto the connecting pebbled and sea weeded land I wondered if I could make it to Ynys Berchen, but after scrambling back up the small rock shelf toward the Lighthouse I peered out and saw four small figures just turning their backs on the summit of the northerly island and heading back towards the Lighthouse.  My chance had gone as it would be unfair to keep everyone waiting another half an hour or so as I went over, gathered data and came back.  On occasions such as this I often reflect and store the memory of want, by doing so it encourages further visits, and these islands deserve that.  All too soon it was time to depart, we headed down to the metalled ladder and got back on the RIB and pulled out of the small, sheltered bay. 

Rob on his way down the ladder to the RIB

Getting ready to leave Ynysoedd y Moelrhoniaid.  Photo: RibRide

On our way back to Ynys Môn the islets of Ynysoedd y Moelrhoniaid were being enveloped by late afternoon high grey cloud as showers pushed in from the Irish Sea.  The RIB swept around their northern extremity before plunging back toward the Marina.  I looked back and the elongated profile of these wonderful rock strewn islets were now dark and silhouetted against the late afternoon sky, their illuminated colour now gone, replaced with a heartening profile of mystery and beckoning. 

The last view of Ynysoedd y Moelrhoniaid, now no more than a silhouette

Survey Result:

Ynysoedd y Moelrhoniaid 

Summit Height:  21.7m (converted to OSGM15) (Double Sub Twmpau addition)

Summit Grid Reference:  SH 26777 94759

Bwlch Height:  not applicable

Bwlch Grid Reference:  not applicable

Drop:  21.7m

Dominance:  100.00%

Ynys Arw 

Summit Height:  15.2m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision)

Summit Grid Reference:  SH 26647 94598 (Trimble GeoXH 6000)

Bwlch Height:  0.0m (LIDAR)

Bwlch Grid Reference:  SH 26690 94671 (LIDAR)

Drop:  15.2m (Trimble GeoXH 6000 summit and LIDAR bwlch) (Pellennig addition confirmed) 

Dominance:  100.00% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For further details please consult the Trimble survey spreadsheet click {here}

© Crown: CHERISH PROJECT 2019. Produced with EU funds through the Ireland Wales Co-operation Programme 2014-2020. All material made freely available through the Open Government Licence.