The Irish Sea: intervisibility of landscapes.

Recently, prompted by a daughter going off to study ancient history, I re-read an interesting and important paper - 'Fluid Horizons' by Aaron Watson in The Neolithic of the Irish Sea: Materiality and traditions of practice, Oxbow Books, 2004, pp.55-63.

The piece is important not least because, for the overwhelming majority of people who don't live in the right places, there is no recognition that distant lands are in fact visible from any given location and that the degree of visibility changes, sometimes dramatically so.

The Isle of Man under superrefraction as seen at ~86km from the north coast of Anglesey at 100m amsl. Notice the effect is apparent over the distance to the IoM, but the ship at far fewer km out to sea is unaffected from this vantage point.

 

Reducing Watson's paper to the bare essentials, the idea is that the coastal regions of the Irish Sea, centred loosely on the Isle of Man, make up a realm that, from height, can be perceived visually.

Watson gives photographic examples of intervisibility, but these are for the most part from various heights in mountainous parts. He does mention the case of Barclodiad y Gawres' view of Ireland, which is achieved from only about 9m above sea level. But the examples I give here are from just under 100m amsl, showing that mountainous terrain per se is not required for intervisibility in the Irish Sea region.

Container ship off the coast of California, with a superrefracted, inverted image above. The enhanced vertical extent can render objects visible from extended distances.

Watson also briefly mentions "mythologies" of islands appearing on the horizon, though the reference he cites for this - The Enchanceted Lands: Myths and legends of Britain's landscapes, Janet and Colin Bord, Harper Collins, 1995 - draws on one book in a series by that husband-and-wife team that is decidedly of its period and very much plays up the 'New Age' magical, mysterious and mythical elements. That is a particular genre with a particular audience and which we might say does not qualify much as academically-authoritative, however well-intentioned.

Despite the potential shortcomings of that book series, the authors were certainly on to something concrete. After 13 years of living on a low hill (Mynydd Parys) on the north coast of Anglesey, I can testify that changing atmospheric conditions lead to interesting effects in respect of the visibility of Irish Sea locations.

Key in this regard is the phenomenon of Fata Morgana - more technically described as superrefraction. Though it may be more common in colder climates, it nevertheless is conclusively shown from my own and many others' examples to occur anywhere, notably over the sea, the conditions are right. It is by no means a rare phenomenon around the Irish Sea coasts, arising perhaps half a dozen times a year or so.

Most commonly, superrefraction appears when the sea is cold and the weather has suddenly snapped to a hot period, giving rise to a steep temperature gradient over the sea. This can sometimes lead to the spectacular vision of a ship at sea sailing along with a perfect inverted image of itself hovering immediately above. More commonly, it leads to ever-changing, imperfect images of distant lands, often taking the form of partial images with flattened, plate-like tops as light hits a strong refracting boundary.

'Castles in the air' - Mourne mountains, Northern Ireland, appear at 138km from Anglesey as vertically enhanced with tower-like projections - a result of inverted images of the hills. Slieve Donard at right.

 

Mourne mountains under very clear but non-superrefracting conditions. The apparent height is much reduced, relative to that under superrefraction.

Mourne mountains under superrefraction, showing strong horizontal distortion as well as vertical enhancement.

Inevitably, superrefraction will have been an important element in enhancing the view of far-off lands that would, then as now, seem magical and bizarre to people. They would have struggled to explain the phenomenon and no doubt found the images, sometimes displaying castle-like vertical enhancements, a strong draw to investigation.

Cumbria, at 140km, seen from the north coast of Anglesey, with modest backlighting rendering the scene much more visible than is ordinarily the case. Cumbria is indeed rarely visible from this location at all.

 

In future discussions of intervisibility across the Irish Sea and indeed elsewhere, it will be crucial to recognise and take into account the unique and mesmerising role of superrefraction. Other effects, such as the backlighting (silhouetting) evident in the image of Cumbria, snow cover (highlighting landscape features) and variable transparency also need to be taken into account. Even clouds, notably towering cumulus and related species should be considered, as these frequently form over the Isle of Man and Cumbria, revealing the position of those landscapes, if not necessarily their form on any given occasion.