Depression in the United Kingdom saw the loss of almost half of the coal pits in the South Wales Coalfield, and their number declined further in the years following World War II. This number is now very low, following the UK miners' strike (1984–85), and the last 'traditional' deep-shaft mine, Tower Colliery, closed in January 2008. Despite the intense industrialisation of the coal mining valleys, many parts of the landscape of South Wales such as the upper Neath valley, the Vale of Glamorgan and the valleys of the River Usk and River Wye remain distinctly beautiful and unspoilt and have been designated Sites of Special Scientific Interest. In addition, many once heavily industrialised sites have reverted to wilderness, some provided with a series of cycle tracks and other outdoor amenities. Large areas of forestry and open moorland also contribute to the amenity of the landscape. Industrialised areas in the 19th and 20th centuries Merthyr Tydfil () grew around the Dowlais Ironworks which was founded to exploit the locally abundant seams of iron ore, and in time it became the largest iron-producing town in the world. New coal mines were sunk nearby to feed the furnaces and in time produced coal for export. By the 1831 census, the population of Merthyr was 60,000—more at that time than Cardiff, Swansea and Newport combined—and its industries included coal mines, iron works, cable factory, engine sheds and sidings and many others. The town was also the birthplace of Joseph Parry, composer of the song Myfanwy. The Heads of the Valleys towns, including Rhymney, Tredegar and Ebbw Vale, rose out of the industrial revolution, producing coal, metal ores and later steel. Aberfan: The Merthyr Vale colliery began to produce coal in 1875. Spoil from the mine workings was piled on the hills close to the village which grew nearby. Tipping went on until the 1960s. Although nationalised, the National Coal Board failed to appreciate the danger they had created. In October 1966, heavy rain made the giant coal tip unstable, resulting in the Aberfan disaster. The recent dumping of small particles of coal and ash known as 'tailings' seems to have been partly responsible. A black wave tore downhill across the Glamorganshire Canal and swept away houses on its path towards the village school. 114 children and 28 adults were killed. The Rhondda Valleys (Rhondda Fach and Rhondda Fawr) housed around 3,000 people in 1860,