Changing Sea-levels

Drowned Channel of Portmagee

The changing sea-levels shows the detrimental effects clearly on the Portmagee Channel in Kerry.

Copyright Arnold Horner 2006.

Drowned Channel of Portmagee
Copyright Arnold Horner 2006.

Drowned Channel of Portmagee

The changing sea-levels shows the detrimental effects clearly on the Portmagee Channel in Kerry.

Copyright Arnold Horner 2006.

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Another of the effects of glaciation

Antarctic Ocean

The evidence of changing sea-levels on the Antarctic Ocean.

Image courtesy of the Irish Independent.

and deglaciation has been to produce sea-level change. The weight of huge thicknesses of ice depressed land areas which took some time to readjust when deglaciation occurred.

Malin Head, Co. Donegal

Photo of Malin Head, Co. Donegal.

Courtesy of Corinna Schleiffer

Malin Head, Co. Donegal
Courtesy of Corinna Schleiffer

Malin Head, Co. Donegal

Photo of Malin Head, Co. Donegal.

Courtesy of Corinna Schleiffer

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As a result some land areas were flooded

Flood at High Tide

This flood stemmed from the Pacific Ocean and is the result of fluctuating sea levels.

Copyright World View of Global Warning 2006.

by the sea but later rose high above sea level, producing 'raised beaches'. Near Malin, in Inishowen, Co. Donegal, raised beaches occur at 25 metres above present sea level.

Around Ireland generally however, there is also evidence that the sea-level has at times been significantly lower than present. Along the south-west and south coasts, for example at the mysterious near-enclosed Lough Hyne and at such places as Kinsale and Cork harbours, the sea appears to have partly drowned valleys that formed in relation to a lower sea level. Along some other parts of the coast there are submerged channels associated with the main rivers, indicating that these rivers once extended much further and to much lower levels. A buried channel of the River Liffey has been identified in Dublin Bay.

Other buried channels have been identified beyond the present mouths of the Rivers Suir and (Munster) Blackwater.

Raised beaches at Ballyhillin, near Malin Head.

At various times in the past, sea-level has been different to what it is to-day. Two types of former shoreline, or ‘raised beach’, are etched into the landscape at Ballyhillin, near Malin Head in County Donegal. The crescentic curve of the village in the middle of the photograph marks a shoreline that existed near the end of the Ice Age. At that time land along parts of the north coast was still recovering from the huge mass of ice that had rested on it. The land was depressed and had yet to readjust, with the result that the sea covered areas that later rose to become dry land. This shoreline is about 20 metres above present sea level. A second shoreline lies between the village and the sea, and is denoted by a line of low cliffs. This old shoreline lies about four metres above the present sea level and marks a period of world-wide high seas during a warm phase about five thousand years ago. [From work cited by Professor Frank Mitchell].

Image courtesy of Cambridge University air photo collection by J.K. St. Joseph.

Raised beaches at Ballyhillin, near Malin Head.
Image courtesy of Cambridge University air photo collection by J.K. St. Joseph.

Raised beaches at Ballyhillin, near Malin Head.

At various times in the past, sea-level has been different to what it is to-day. Two types of former shoreline, or ‘raised beach’, are etched into the landscape at Ballyhillin, near Malin Head in County Donegal. The crescentic curve of the village in the middle of the photograph marks a shoreline that existed near the end of the Ice Age. At that time land along parts of the north coast was still recovering from the huge mass of ice that had rested on it. The land was depressed and had yet to readjust, with the result that the sea covered areas that later rose to become dry land. This shoreline is about 20 metres above present sea level. A second shoreline lies between the village and the sea, and is denoted by a line of low cliffs. This old shoreline lies about four metres above the present sea level and marks a period of world-wide high seas during a warm phase about five thousand years ago. [From work cited by Professor Frank Mitchell].

Image courtesy of Cambridge University air photo collection by J.K. St. Joseph.

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Apart from the sea level changes associated with glacial events, sea levels may have changed as a result of earth movements. The drowned river valleys, just like the curiously-patterned onshore drainage systems of Munster and the extraordinary gorge on the River Barrow at St. Mullins, Co.Carlow, may yet prove to be best interpreted in relation to some sort of tilting of southern Ireland. The geological history of our coastline remains imperfectly understood.