Summary of site:
From Ballymartin Hill, 4 km north east of Kilkeel, to Dunmore Hill, 4 km north of Annalong the gently sloping coastal plain has a stepped profile that runs roughly parallel with the coast. The highest step is 30 m above sea level (asl) with another at 20 m asl between Mullartown and Annalong that continues south west to within a kilometre of Ballymartin Hill. These steps, often described as notches, are a consequence of severe coastal erosion at a time when sea level was much higher than at present.
When thick ice sheets accumulate on land as they did during the last major glaciation in Ireland (the Midlandian), the load of ice depresses the rocks into more plastic levels below the Earth’s brittle crust. When the ice melts, the load is lost but the land does not rebound immediately but adjusts spasmodically over a period of thousands of years. This means that in the early stages the land remains depressed and sea level is higher, further enhanced by meltwater added during the deglaciation. Coastal erosion cut a cliff in the glacial deposits that smothered the north east Mourne coastal plain, first at the 30 m level then, after a period of vertical adjustment, at the 20 m level.
Between Glasdrumman and Annalong there is a third notch, in this case cut into late glacial beach deposits, at the 10 m asl with an equivalent terminating a moraine ridge in Newcastle. An exposure south east of Dunmore Cottages shows the nature of the beach deposits.