Mynydd Merthyr is a broad ridge of high ground between Taff Vale ( Welsh Cwm Taf) and the Cwm Cynon in the Valleys region of South

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

. It forms the boundary between the unitary authorities of

Rhondda Cynon Taff Rhondda Cynon Taf (; RCT; also spelt as Rhondda Cynon Taff) is a county borough in the south-east of Wales. It consists of five valleys: the Rhondda Fawr, Rhondda Fach, Cynon, Taff () and Ely valleys, plus several towns and villages away from ...

to the west and

Merthyr Tydfil Merthyr Tydfil () is the main town in Merthyr Tydfil County Borough, Wales, administered by Merthyr Tydfil County Borough Council. It is about north of Cardiff. Often called just Merthyr, it is said to be named after Tydfil, daughter of K ...

to the east. The high point of 493m is at Mynydd Gethin (OS grid reference SO 044025) (though the summit

trig point A triangulation station, also known as a trigonometrical point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity. The station is usually set up by a map ...

is at the lower height of 491m) is the culmination of a long ridge which extends northwestwards from the confluence of the Afon Cynon and the

River Taff The River Taff () is a river in Wales. It rises in the Brecon Beacons as two rivers, the Taf Fechan ("little Taff") and the Taf Fawr ("great Taff") before becoming one just north of Merthyr Tydfil. At Cardiff, it empties into the Bristol Chan ...

Abercynon Abercynon () is a village and community (Wales), community (and electoral ward) in the Cynon Valley within the unitary authority of Rhondda Cynon Taf, Wales. The community comprises the village and the districts of Carnetown and Grovers Field to ...

. The ridge includes the subsidiary summits of Twyn Brynbychan and Twyn Sych. To the northwest lies Mynydd Aberdâr. Much of the hill has been planted with

coniferous forest Conifers () are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All e ...

. Its flanks are heavily scarred by mining. The village of

Aberfan Aberfan () is a former coal mining village in the Taff Valley south of the town of Merthyr Tydfil, Wales. On 21 October 1966, in the Aberfan disaster, a colliery spoil tip collapsed into homes and a school, killing 116 children and 28 adults. ...

sits at the foot of its eastern slopes, the scene of the

Aberfan disaster The Aberfan disaster () was the catastrophic collapse of a colliery spoil tip on 21 October 1966. The tip had been created on a mountain slope above the Welsh village of Aberfan, near Merthyr Tydfil, and overlaid a natural spring. Heavy rai ...

on 21 October 1966 when a coal tip above the village slipped and engulfed the village school killing 144 people of whom 116 were children.

Geology

The entire hill is composed of sandstones and mudstones dating from the

Carboniferous Period The Carboniferous ( ) is a geologic period and system of the Paleozoic era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the Permian Period, Ma. It is the fifth and penultimate perio ...

. There are also numerous

coal seam Coal mining is the process of extracting coal from the ground or from a mine. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extrac ...

s within the sequence, most of which have been worked. The upper part of the hill including the summit plateau is formed from the

Pennant Sandstone The Pennant Measures is the traditional name for a sequence of sedimentary rocks of the South Wales Coalfield. They were also referred to as the Upper Coal Measures and assigned to the Westphalian 'C' and Westphalian 'D' stages of the Carbonifer ...

, a rock assigned to the Carboniferous Upper Coal Measures. The flanks of the hill owe their steepness in part to the action of glacial ice during the succession of

ice ages An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and Gre ...

Access

Virtually all of the afforested areas and some adjoining areas of moorland are classed as

open country "Open Country" is a designation used for some access land in England and Wales. It was first defined under the National Parks and Access to the Countryside Act 1949 (and extended by the Countryside Act 1968), and was land over which an appropr ...

under the CRoW Act giving a right of access to walkers. In addition there is a limited network of

public footpath A footpath (also pedestrian way, walking trail, nature trail) is a type of thoroughfare that is intended for use only by pedestrians and not other forms of traffic such as motorized vehicles, bicycles and horses. They can be found in a wide va ...

s and other public rights of way which give access to parts of the hill.Ordnance Survey 1:25,000 scale Explorer map series, sheet 166 ''Rhondda & Merthyr Tydfil/Merthyr Tudful''

References

{{coord, 51, 42, 18, N, 3, 22, 23, W, dim:5000_region:GB, display=title Mountains and hills of Merthyr Tydfil County Borough Mountains and hills of Rhondda Cynon Taf