Previous SiteNext Site

ArmoyAntrim
No picture
Summary Full report
Site Type: Inland exposure
Site Status:
District:
Grid Reference: X295429, X29782317, X30674328, X31084391
Rocks
Rock Age: Quaternary
Interest
Other interest: No data, Glacial feature, Glaciotectonic, drumlin, moraine ridge

Summary of site:

Events in glacial periods are notoriously difficult to read because continental ice sheets generally obliterate almost everything that preceded them either by grinding it down or sweeping it away. All that is left when they finally melt is ice-moulded bedrock and the enormous spreads of material carried under, within and on top of the ice and even that can be reshaped by meltwater or later erosion. The skill is in recognising the surviving landforms and reading the information they contain. The deposits extending 16km south west of Armoy and 9km to the north east present exactly these kinds of problems.

The chief features in the area are strongly defined ridges, the most westerly being the Secon Ridge, with a high point of 83m, that extends from the north-west outskirts of Ballymoney for 5km further to the north west. The second, the Ballymoney/Stranocum Ridge, is more sinuous and extends from the north-east outskirts of Ballymoney to Stranocum where it terminates on the west bank of the River Bush. Its maximum height is 73m. The third is the Dervock/Armoy Ridge. It starts just south east of Dervock, passing briefly east then east north east to Armoy before swinging for 9km along the eastern side of Glentaisie. It ends at Broombeg a couple of kilometres east of Carneatly. All the ridges average 3km in width with a maximum of 5km. The three were almost certainly a single ridge complex originally but meltwater channels, and later the River Bush, breached them to isolate the three features we see now. The ridges are part of a single long moraine formed along the front of a massive continental ice sheet flowing south and south east across parts of modern Scotland. The moraine accumulated at a time when the ice margin appeared to be stationary but actually was advancing and melting at the same rate. All the debris scoured from the bedrock was released in the thaw and accumulated, banked against the edge of the ice sheet, as this vast ridge. Granite boulders in the moraine cannot be matched in Northern Ireland and resemble Scottish granites, strongly suggesting their Scottish origin. While this was happening, the ice from the sheet centred on the Lough Neagh basin was flowing north and slightly east towards this margin. In the space between the two ice fronts, in a long depression, a large glacial lake was being fed with sediments discharging in strong streams pouring from beneath the ice along both margins. Later a further climatic deterioration reactivated the northern ice sheet, causing it to flow over the moraine, planing and faceting its high points in the process. This was the final push of the Scottish ice before it quickly melted and retreated north. The Lough Neagh basin ice continued to flow north during this retreat. It too was decaying and by this time was too thin to plough up the sediments and the moraine. It flowed over them, streamlining the unconsolidated surface as it passed, creating drumlins (egg-shaped hills moulded by flowing ice) on the higher ground and to the west. This ice, too, finally receded to its ice centre leaving a landscape of sands, gravels and boulders easily and massively eroded by the torrential meltwaters. It was in the hollows of these bleak expanses that lakes accumulated, creating the conditions for the formation of bogs as the climate warmed and plants began to green the land. This area preserves evidence of a unique set of conditions at the end of the final glaciation around 12,000 years ago. The distorting effects of ice overriding glacial deposits are stamped on the land. The near closing of the two major ice fronts is also imprinted on this landscape. There is little sand and gravel extraction in the area, largely because the sediments are too mixed; threats other than sand and gravel workings are minimal.


Previous SiteNext Site

|Home|