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Croaghaun, with its summit hidden in the mist, Achill Island. Photo by Richard Creagh

Ireland’s Highest Cliff?

Scrolling through my Facebook feed a while ago I noticed a post on a Wild Atlantic Way group discussing Ireland’s highest cliff. The poster was making the case for Sliabh Liag in County Donegal over Croaghaun on Achill Island in County Mayo. The post attracted over 200 comments and plenty of argument back and forth. One commenter raised the issue of ‘precipitous-ness’. Intrigued by this, I decided to dig into this question a little.

Firstly, I should say that I’m not a geographer or a geologist or an expert of any sort in any related field. But, as the author of a rock climbing guide to Ireland and a book on the Wild Atlantic Way I have a particular interest in this subject.

In essence I think there are two questions that I’m going to attempt to answer – What is the definition of a cliff and which of the two main contenders should be declared the highest?

What is a cliff?

According to Wikipedia a cliff is “an area of rock which has a general angle defined by the vertical, or nearly vertical.” Ok, that’s reasonably clear, however, they then say:

“Given that a cliff does not need to be exactly vertical, there can be ambiguity about whether a given slope is a cliff or not and also about how much of a certain slope to count as a cliff.  Listings of cliffs are thus inherently uncertain.

Wikipedia entry on ‘cliffs’

Yikes, so not all that helpful then. The bottom line here is that there isn’t a definite angle that a slope must be to qualify as a cliff.

A Climber’s Perspective

If you asked a climber to define the term cliff, they might say – a slope steep enough to require climbing ie. use of the hands as well as the feet. So what angle is this? Well, obviously it depends on the friction of the rock and the abundance and shape of the holds, but broadly speaking I’d say around 45°.

A Rough Angle

So let’s take 45° as the approximate angle at which a slope could be considered a cliff. This measurement should be the average angle from the bottom to the top calculated by simple trigonometry using the vertical and horizontal height difference.

Obviously, you need to decide where the cliff starts and finishes to calculate these numbers and that is what makes the process very subjective.

The Main Contenders

There are two cliffs on the west coast of Ireland that are claimed to be the highest on the island – Sliabh Liag in Donegal and Croaghaun on Achill Island in Mayo.

One of the issues that comes up often is that, as neither are particularly steep, advocates of one tend to claim that the other isn’t a cliff or isn’t for its full height.

Sliabh Liag

HEIGHT 595m
DISTANCE 840m
AVERAGE ANGLE 35°

In southwest Donegal the Glencolmcille peninsula, which juts out into the Atlantic, has no shortage of very rugged and impressive coastline on both its northern and southern sides. However, the tallest and most famous section lies on the south coast at Sliabh Liag (sometime spelt Slieve League). 

The cliffs are a popular tourist sight and a destination signature point on the Wild Atlantic Way. At the eastern end of the cliffs at Bunglass, a headland sticks out, accessible by road and with a large car park, it’s a very convenient viewing point.

Wikipedia claims that the cliffs rise to 601m above the Atlantic, but according to Ordnance Survey Ireland the highest point, the summit of Slieve League, lies 595m above sea level, so Wikipedia is a little off.

The issue with Sliabh Liag is whether the entire slope that runs from the sea to the summit can be considered a cliff. As is clear in the photo at the top of the page, there are some vertical sections of rock, but there are also many lower-angled vegetated slopes.

The numbers I have quoted above refer to a straight line connecting the highest point on the ridge to the sea. The average angle is 35°, which I feel is on the low side for a cliff. Slightly further east there are steeper sections, which, although they aren’t as tall, reaching 540m, have an average angle of 48°.

One fact that’s worth mentioning is that there are undoubtedly cliffs at Sliabh Liag that would rival the Cliffs of Moher for both height and steepness. This point can be lost, visually and conceptually, due to the scale of the surrounding terrain.

Achill Island

HEIGHT 688m
DISTANCE 735m
AVERAGE ANGLE 42°

The northwestern coast of Achill Island in Mayo consists of a line of cliffs that run for over 6km between the jutting headlands of Saddle Head and Achill Head. The highest point is the summit of Croaghaun, which stands 688m above the Atlantic. The slopes, which consist of a mix of rock and vegetation, have an average angle of 42°, so I think that they qualify as cliffs.

There is another summit to the southwest, known as Croaghaun SW Top, it’s slightly lower at 664m, but its northern slopes are even steeper with an average angle of 48°.

The view from Croaghaun.

The Winner?

It’s very clear, give the numbers above, that Croaghan is both higher and steeper than Sliabh Liag.

What About Inland Cliffs?

So far we have been only discussing sea cliffs. But are there any inland cliffs that rival the two big sea cliffs? To do so they would have to be nearly 700m tall and have an angle of over 45°. According to Wikipedia there are 102 mountains with an altitude greater than 688m. However, very few of them either have steep slopes or the necessary height gain.

There is one exception that immediately springs to mind – the north face of Carrauntoohil.  The north face of Ireland’s highest mountain is steep, rocky and characterised by a number of jagged ridges. But is it high and steep enough?

Here’s where things get a little tricky.

The north face is divided by into upper and lower sections by a diagonal ledge that runs across the face called the Heavenly Gates.  The upper face is home to number of rock climbs including the classic scramble/easy climb Howling Ridge.

The lower section starts a short distance above the shore of Lough Gouragh. If you measure the cliff starting from the lake shore then the vertical distance to the summit is 695m which would make it the tallest cliff in Ireland. The average angle would be a respectable 42°.

However, I think this is stretching the definition of a cliff too far. It’s clear from the photo above, and the map contours, that the cliff doesn’t start right at the lake. There is a stretch of reasonably steep grass for the first 40m or so vertical meters before the cliff proper starts.

This means the true vertical height of the north face is more like 650m, giving an average angle of 46°.

The Cliffs of Moher. Photo by Thomas K

Other Notable Cliffs

There are a number of other immense cliffs along the west coast, and while they aren’t in the same league height-wise as the big two, they are all very impressive and well worth seeking out.

The Cliffs of Moher

HEIGHT 200m
DISTANCE 50m
AVERAGE ANGLE 75°

According to Wikipedia at their highest point, the world-famous Cliffs of Moher in County Clare are 214m tall. This is incorrect, at least according to Ordnance Survey Ireland, on their map the top of the cliffs just about reach the 200m contour. This incorrect figure of 214m is quoted all over the internet and seems to have originated with Discover Ireland.

In terms of steepness you can’t fault the Cliffs of Moher. For example the cliff in the image above, the stretch just north of Knockardakin, is 190m high and close to plumb vertical for the entire height. Certainly a contender for the tallest steep cliff in Ireland.

Benwee Head. Photo by Richard Creagh

Benwee Head

HEIGHT 100m
DISTANCE 30m
AVERAGE ANGLE 73°

While ‘only’ 100m tall the cliffs at Benwee Head in North Mayo are steep, spectacular and little known. And there are plenty of other cliffs along this stretch of coast that aren’t quite as sheer but are more than twice as high.

Fair Head

Fair Head

HEIGHT 100m
DISTANCE 5m
AVERAGE ANGLE 87°

Fair Head lies on the Antrim shore facing north towards Rathlin Island. Running for also 5km the dolerite cliffs rise vertically for 100m from a steep scree slope and ending abruptly at a grassy plateau. A short distance from the Giant’s Causeway, the cliffs share a similar structure of vertical columns. The cliff is home to over over 400 rock climbs and is considered one of the best crags in Britain or Ireland.

If you enjoyed this post then you might consider ordering a copy of one of my books. Exploring Ireland and Exploring Ireland’s Wild Atlantic Way may well be of interest.

In Conclusion

So after all this what conclusion can we draw?

Croaghaun is the highest cliff in Ireland, it is also the highest sea cliff

The second highest cliff is the north face of Carrauntoohil, it is also the highest inland cliff

Irrespective of all this, the main thing is to appreciate that we are blessed with many beautiful cliffs along our coasts and in our mountains and that is all that really matters.

Three Rock Books