The Giant's Causeway is an area of about 40,000 interlocking basalt columns, the result of an ancient volcanic eruption approximately 50 to 60 million years ago. It is also known as Clochán an Aifir or Clochán na bhFomhórach in Irish. It is located in County Antrim on the northeast coast of Northern Ireland, about three miles (4.8 km) northeast of the town of Bushmills. It was declared a World Heritage Site by UNESCO in 1986, and a national nature reserve in 1987 by the Department of the Environment for Northern Ireland. In a 2005 poll of Radio Times readers, the Giant's Causeway was named as the fourth greatest natural wonder in the United Kingdom.