Mapping Mountains – Hill Reclassifications – The 500-Metre Tops of England and Wales – Deweys

Iwerddon (SH 688 482) – Dewey deletion

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Deweys and where I have had direct association with the status change.  These posts will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the Mountain tables book.

Iwerddon (SH 688 482)

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.

This list formed one of a number of lists that appeared in the Mountain tables book published by Constable in 1995 and at the time of publication comprised 373 hills with 164 in England, 5 in the Isle of Man and 204 in Wales.  The Deweys have undergone extensive revision since first publication with the initial stages forming the basis of this revision given below:

1995    Mountain tables published by Constable with 373 hills listed as Deweys.

April 2000    Strider (LDWA quarterly booklet) publishes contact details for David Purchase and Myrddyn Phillips who have found and list 24 and 14 possible new 500m tops respectively.

It was expanded versions of the above two lists that formed the basis of the next publication:

25^th May 2000    List of Possible 500 Metre Tops by Michael Dewey listing 44 hills.

David Purchase expands his Additional Dewey 500m Hills and Myrddyn Phillips produces lists of English 500m hills to measure and Welsh 500m hills to measure.

These lists formed the basis of the next publication:

29^th June 2000    Possible/Probable 500’s by Michael Dewey listing 77 hills.  Michael adopts following protocol; if one person proposes that a top should qualify as a 500 by personal survey, and is then confirmed by a second person, it should then be promoted to the main list.

April 2002    The 500+ Tops of England and Wales – The ‘New Deweys’ published in the Strider booklet and listing 66 new qualifying hills.

25^th May 2006    Rob Woodall republishes Michael’s main and possible/probable lists on the RHB Yahoo group file database. 

The details for this deletion appear below:

The name the hill was listed by in the Deweys is Iwerddon, and it is adjoined to the Moelwynion group of hills which are situated in the north-western part of north Wales, and it is positioned with the A498 road to its north-west and the A470 road to its east, and has the town of Blaenau Ffestiniog towards the south south-east.

This hill was not included in the original 1995 Constable publication, but with a 583m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and bwlch contouring between 550m – 560m on the 1:50,000 Landranger and 1:25,000 Explorer map, the interpolated drop value was estimated sufficient for this hill to be a potential new Dewey. 

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

The above detail was noted by David Purchase and Myrddyn Phillips who worked independently but also exchanged all data.  These details were forwarded to the list author; Michael Dewey and the hill was added to the list on the 3^rd May 2000.  Subsequently Myrddyn Phillips conducted a basic levelling survey of this hill on the 5^th May 2000 without prior knowledge of its recent inclusion, resulting in the hill considered to have just over 30m of drop.

Doing the sums after the level and staff line survey

As the result from the basic levelling survey was near the minimum 30m qualifying drop value, this hill was prioritised for a line survey which was conducted by John Barnard and Myrddyn Phillips on the 11^th March 2010, resulting in 25.2m of drop and this hill’s deletion from Dewey status.

The full details for the hill are:

Name:  Iwerddon

OS 1:50,000 map:  115

OS 1:25,000 map:  17

Summit Height:  583m (spot height)

Summit Grid Reference:  SH 68822 48217 (hand-held GPS during line survey)

Bwlch Height:  558m (relative to spot heighted summit and line surveyed drop)

Bwlch Grid Reference:  SH 68409 47880 (hand-held GPS during line survey)

Drop:  25.2m (level and staff line survey)

Myrddyn Phillips (September 2020)