Mapping Mountains – Hill Reclassifications – Humps

Cefn yr Ogof (SH 916 773) – Subhump reclassified to Hump

This is the tenth in a series of Hill Reclassification posts that detail hills whose status has been altered in the listing of the Humps (HUndred Metre Prominences) through map study and / or surveys that I have instigated.

Cefn yr Ogof (SH 916 773)

This and forthcoming posts are retrospective as many of these hill reclassifications were initiated from studying the Ordnance Survey enlarged mapping that is hosted on the Geograph website, and for the reclassifications that affected the Humps the email I posted on the RHB Yahoo Group forum in relation to this hill was dated 23.05.12.

The listing of Humps was published in book format by Lulu in 2009 and entitled More Relative Hills of Britain, its author; Mark Jackson gives credit to a number of people who contributed toward the formation of this list, these include; Eric Yeaman, Alan Dawson, Clem Clements, Rob Woodall, Bernie Hughes, Pete Ridges and others.  When the list was published in book format there were 2987 Humps listed with their criteria being any British hill that has 100m or more of drop, accompanying the main list is a sub category entitled Subhumps, with the criteria being any British hill that has 90m or more and below 100m of drop.

More Relative Hills of Britain by Mark Jackson

The details for the reclassification appear below:

There has been a reclassification to the listing of the Humps (HUndred Metre Prominences) due to consulting the Ordnance Survey enlarged mapping that is hosted on the Geograph website, with these details being posted on the RHB Yahoo Group forum on 23.05.12.

Prior to this notification Mark Jackson had listed this hill as a Subhump with c 97m of drop based on the 204m summit spot height given to a triangulation pillar on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 107m based on bwlch contouring at 10m intervals.  Subsequently bwlch contour interpolation was helped by the use of 5m contour intervals on the Ordnance Survey enlarged mapping hosted on the Geograph website and therefore the estimated bwlch height could be better refined to c 103m – c 104m, and when coupled with this hill’s 204m summit spot height these values give this hill c 100m – c 101m of drop, which is sufficient for it to be reclassified to Hump status.

Extract from the Ordnance Survey enlarged mapping hosted on the Geograph website showing the 5m contour intervals at the bwlch of this hill

The hill is adjoined to the Rhos group of hills and is situated overlooking the A 547 and A 55 roads and the coast which are to its north and the Afon Dulas which is to its west, with the village of Llanddulas to the north-west of the hill.

The addition of this hill to Hump status was accepted by Mark Jackson and its new classification augmented in to the listing of the Humps on the 19.07.12.

Cefn yr Ogof was subsequently surveyed by John Barnard, Graham Jackson and Myrddyn Phillips on the 23.01.14 using a Leica GS15 and a Trimble GeoXH 6000, resulting in this hill having a 204.5m (converted to OSGM15) summit height and a 102.9m (converted to OSGM15) bwlch height, with these values giving this hill 101.6m of drop.

Gathering data with the Leica GS15 at the summit of Cefn yr Ogof

The full details for the hill are:

Name:  Cefn yr Ogof

Summit Height:  204.5m (converted to OSGM15)

OS 1:50,000 map:  116

OS 1:25,000 map:  264

Summit Grid Reference:  SH 91684 77301

Drop:  101.6m (converted to OSGM15)

Myrddyn Phillips (September 2017)

Mapping Mountains – Trimble Surveys – Mynydd Hiraethog

23.01.14  Cefn yr Ogof  (SH 916 773)

The upper slopes of Cefn yr Ogof (SH 916 773)

For a number of years Cefn yr Ogof languished as a Sub-HuMP with a listed drop of 97m, but with 5m contour intervals on the Ordnance Survey enlarged mapping on the Geograph website with bwlch contouring between c 100m – c 105m and with a map height of 204m the hill was a likely candidate for promotion to full HuMP status.  This was proposed to the hill bagging community in May 2012 and accepted as a fully-fledged HuMP in July 2012.  Cefn yr Ogof is currently listed as a HuMP with 101m of drop.

The hill is positioned in the north-west of the Mynydd Hiraethog range and overlooks the busy A55 and the north Wales coast.  It is part of limestone country with many outcrops on the hill’s upper slopes as well as on adjacent hills.

Today’s outing was the first with G&J Surveys that included the Trimble.  We met at John’s house in Mold and headed west toward the area of the bwlch which is near Abergele.

The bwlch is in a field, we sought access permission at a number of houses, this failed disastrously as the residents were either hiding from us or out, as no one answered.  However, we did speak with a farmer, who we flagged down as he steamed his way up the narrow country lane in his tractor.  It wasn’t his field but he didn’t express any objection to us wandering around with a multitude of flags and putting surveying equipment up.

An hour or so later and we had pinpointed the position of the critical bwlch.  This was done by setting out a grid of flags and taking readings to each one with a level and staff.  Once completed the readings give the relative height of the land as it ascends on the valley to valley traverse and descends on the hill to hill traverse.  It is an easy and effective way to pinpoint the position of a critical bwlch. 

The Leica GS15 set up position at the bwlch of Cefn yr Ogof

The Leica GS15 had been set up before doing this, once it had gathered over an hour’s worth of data we packed it away and took a reading from its set up position to the actual position of the critical bwlch.  The Trimble was then positioned on the latter and gathered 16 minutes of data.

Boys and their toys.  The critical bwlch of Cefn yr Ogof

We then drove to Rhyd- y-foel and headed up the hill.  As John and Graham are both quicker than me I normally try and get a head start and they normally catch me up and overtake me.  I opted for a barbed wired fence, brambly scrub land approach and they opted for a route through a hedge.  Once the obstacles were overcome we converged from different directions about two minutes below the summit.

The summit is a good vantage point and brought back memories of my previous visit when Des Taylor had celebrated his completion of the Welsh and English HuMps. 

By the time the three of us arrived at the summit the wind was blowing and it was bitingly cold.  We set about taking readings to the flush bracket on the trig pillar, to the trig’s base and its top.  The GS 15 was then set up over the highest embedded rock we could find amongst the summit cairn for an hour’s worth of data, whilst the Trimble was set up on the top of the trig for 30 minutes to compare its data set against the relative height we had just attained with the level and staff to the top of the trig and the highest rock.

The Leica GS15 set up over the high point of Cefn yr Ogof

By now the flashes of sunlight had disappeared and greyness had crept from the near sea and descended upon the land.   Away to the north-west the higher peaks of Eryri were swamped in deep cloud.  We all thought it was going to rain and took shelter in the near forest, more out of the wind than the impending shower.  The latter never materialised but the wind was unabating.

After the Leica GS15 was packed away the Trimble was aligned with the high point of the highest embedded rock, secured in place with small rocks and gathered ten minutes of data.  We then headed down out of the wind.  Another excellent day out on the hill and great to be out with G&J again.

The Trimble GeoXH 6000 wedged in place on the high point of Cefn yr Ogof

Survey Result:

Cefn yr Ogof

Summit Height:  204.5m (Trimble GeoXH 6000, converted to OSGM15)  204.5m (Leica GS15, converted to OSGM15)

Summit Grid Reference:  SH 91684 77301

Bwlch Height:  102.9m (Trimble GeoXH 6000, converted to OSGM15)  102.9m (Leica GS15, converted to OSGM15)

Bwlch Grid Reference:  SH 93547 75706

Drop:  101.6m (Trimble GeoXH 6000)  101.6m (Leica GS15)  (Hump status confirmed)

Dominance:  49.69%

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