UKC

So why do some coasts form sea cliffs while others do not? Why is the UK so well endowed with sea cliffs while the US is impoverished? Why does the west coast of Lewis have lots, but Harris and Lewis hardly any? It doesn't seem to be anything to do with rock type, so what factors determine whether a coast forms cliffs or not?

In reply to Robert Durran:

My answer would be that the land has to be high enough (fairly obvious) and the rate of erosion by the sea has to be (or have been) faster than the rate of weathering of the land above sea level. This is more likely to be case if the rock is hard enough to be able to resist those weathering processes and if the site is exposed to significant wave action.

In reply to Robert Durran:

Also is the coast a place where material is being deposited - either from further up the coast or from inland (e.g Bangladesh doesn't have any cliffs (probably)) - or a place where any eroded material is carried away (most west facing coasts in UK).

Disclaimer: not a geologist and just speculating.

In reply to Rog Wilko:

Lewis: low lying, loads of sea cliffs.
Harris: mountainous, almost no sea cliffs.
Uist: low lying, almost no sea cliffs.

All the same rock type and identical exposure to the north Atlantic.

 

In reply to Robert Durran:

Tidal currents, wind direction, river mouths etc.. impact the deposits of sand and shingle, which at as the barrier preventing erosion. Also the depth of the water near the shore effects wave height. 

In reply to Robert Durran:

While googling this topic I discovered that the Solar System's highest cliffs circle Uranus.

 

Snigger.

In reply to Robert Durran:

Could it have something to do with the angle of the rock strata? I'd guess that if they shelve upwards towards the sea, the softer layers can be easily eroded causing rockfalls in the higher levels and eventually forming cliffs. If they shelve downwards towards the sea, there will eventually only be erosion taking place on the surface of a single hard layer.

Just guessing, I know nothing about the subject.

In reply to Robert Durran:

I guess you probably do need to consider rock type, but then there are currents and prevailing winds, sea level changes, tidal reach, wave height and energy, weather/climate, isostatic movement, biological factors (reefs) and more. And after that, how they interact. 

In reply to Bob Kemp:

I guess it's all pretty complicated then.........

In reply to Robert Durran:

Briefly, it is surely to do with immense time as well as rock type and structure. 

Imagine one of your paces as 1million years. If you walked 4600 paces you would reach the earth's beginning. Only 600 paces away the Outer Hebrides were joined to the Appalachians. Within the last two paces there have been about 20 ice ages and interglacials. All our human history has been in the width of your finger nail. 

Look back to four and half thousand paces away. During that immense time, rocks have formed and reformed. Faults have come and gone, mountains lifted and weathered away. 

So, there are sea cliffs in some places and not in others because of a whole series of complicated factors involving erosion, weathering, faulting and different geologies acting over immense time. 

In reply to Robert Durran:im not an expert, but a combination of sea level and ice age paleogeography and topography will have a big impact in Scotland

no sea cliffs in US Robert? Perhaps not in Cali, Flor, but....

 

In reply to Heartinthe highlands:

One of the factors in the Outer Hebrides has been the glaciations. The advancing ice would not have been a sheet of uniform thickness and, after the glacial retreat, the bed rock (Precambrian gneisses) would not have been a perfectly peneplained surface.  Since then there has been a flexural rebound as the lithosphere has unloaded as the icecaps shrank.

In reply to Robert Durran:

It's well known by Douglas Adams fans that Slartibartfast made the Norwegian fjords, maybe he practiced on the UK first?

PS: I AM a geologist

In reply to wbo:

I remember noticing some reasonably large Californian sea cliffs while watching Play Misty for Me. Apparently they are loose and rubbish for climbing.

In reply to Robert Durran:

Interesting question but I think it's the wrong way to ask it, because geology is an ongoing process. More like, why have some coasts formed sea-cliffs now, while others have not? And even then, the answer must be impossibly complex. In a million years, the nature and shape of many coasts will have changed beyond recognition.

In reply to AndyC:

Isn't Slartibartfast a route at the Dubh Loch? And didn't Douglas Adams write that awful Hitchhiker bollocks? Sounds like more bollocks to me.

 

In reply to John2:

I am assured by someone who lives and climbs there that the US is relatively bereft of sea cliffs per km coast compared to the UK. Obviously there are some though!

In reply to Robert Durran: Geology and Geography have nothing to do with it. The sea cliffs were created by God's divine hand, and he put extra effort into creating Gogarth.

 

In reply to Robert Durran:

The British Isles are geologically complex; loads of different rock types within a relatively small area. Perhaps this combined with a long coastline compared to the country's square milage means we have an abundance of sea cliffs.

If you think about mechanisms of erosion in crude terms, the action of the sea is more likely to create cliffs while rain run off from the the land is more likely to wear down the coast. Continents have big landmass/lots of run off. Islands have small landmass/greater coastal erosion due to the sea.

In reply to Martin Haworth:

If he put that much effort in, he made a complete hash of the rock aesthetics and quality then. Mind you, he seems to have a bit of a track record of f*cking things up.

In reply to Robert Durran:

I don't know what you mean. He used some "artistic licence" in the design, the fact you think he made a hash of it just means you're a heathen.

In reply to Martin Haworth:

Maybe better described as having a bit of a piss take as light relief after working on his masterpieces in Pembroke and the Hebrides.

 

In reply to Stichtplate:

Not sure about that. I'd bet the UK has a lot more run off per km of coast than the Pacific coast of the USA. Unless the climate has changed since the cliffs formed.

 

In reply to Robert Durran:

Isn't the pacific North West really rainy?

Edit: my theory is only a guess, if you want a more definitive answer perhaps a geology forum would be a better bet?

 

In reply to Robert Durran:

It's because America is so big and heavy that it's sunk right down into the sea.

Which actually reminds me, there are apparently raised beaches, several metres above sea level, in Scotland because the Scottish land mass is rising since the loss of the ice sheet from the last ice age.  That most likely needs confirming.

In reply to Lusk:

Sounds plausible, but now I'm not sure if anyone is being serious!

I know that Scotland is rising for that reason, but I think England is sinking (?) and the south of England has loads of sea cliffs too.

 

In reply to Robert Durran:

I don't know. You may have found UKC's Achilles heel, doesn't know much about geology!

Scotland is going up due to re balancing after the ice sheet melted and south of England is going down. As people say there are cliffs in california, but they are made of choss. As others have eluded to its due to loads of factors as to why places have sea cliffs. It essentially depends on what happened millions of years ago, which affects what the rocks are made of (world class granite or california sea cliff choss). It also depends on what's happening today. Processes like - is loads of sediment being deposited (e.g. Missisippi delta or Bangladesh) or is there erosion of cliffs (Cornwall, gogarth). There are many other processes that contribute to a greater or lesser extent. Interesting question but hard to answer as there is so much coastline, each bit with its own story to tell. 

 

In reply to Robert Durran:

It's all about what happens to what the sea erodes. If it is washed away you get cliffs. If it is deposited you get beaches. What governs sediment transport/deposition? Wind, waves, tide, currents. Why do the wind, waves, tides and currents deposit sediments in the Uists, but remove them from Lewis? That I don't know. But I'm glad they do.

In reply to Andy Moles:

Ok, so, since lots of people are saying there are loads of factors, maybe narrow it down to my Lewis/Harris/Uist example where most factors are the same, including era!

I'm not convinced rock type can be a major factor since there are loads of chossy, soft cliffs (probably more than good, solid ones, even in the outer Hebrides!). But maybe chossy ones form more readily as well as disintegrating more readily!

 

In reply to Wicamoi:

That seems to make a lot of sense. Still hard to believe it could make such a dramatic difference between Lewis and Uist though!

In reply to Robert Durran:

I agree - particularly as the predominant current in the area is northward. Here's my suggestion. Perhaps shell-sand is washed north in the current from erosion further to the south, and is deposited on the Uists at a rate faster than it is removed by the northward current (strong westerly winds drive it onshore), but of what is removed northwards from the Uists by the current much washes round the top of North Uist in westerly gales and is swept through the Sound of Harris (and ultimately beaches on the NW mainland - Achmelvich, Sandwood etc). What remains of the northward bound sand deposits on Harris, but there is not then enough left to deposit on Lewis at a rate fast enough to outstrip the erosion. 

I am not an expert in sediment transport!

In reply to Wicamoi:

But in that case why hasn't all this sand been swept eastwards into The Minch further south?

In reply to Robert Durran:

Just a bit of speculation. West coast is subject to prevailing wind presumably in contrast to East Coast of North America. I think I'm right in saying that western Scotland at any rate was connected to North America circa 60 million years ago ( you'd have to check the dates but its around that order of magnitude) but would have split up as the atlantic opened ( caused I think by passing)over the mantle plume now under Iceland. What this means is that the west coast of Scotland will have old continental rock which has been subject to folding, ( Appalachians /Scottish Highlands are deeply eroded fold mountains ) then rifting and vulcanism. I'm wondering if it is the folding which is important so that the dip of the rock now exposed to the prevailing wind could be  high angle to the erosive forces which would provoke instability and rock slope failure. The are will also have been subject to glaciation to sea level in the relatively recent past which would also give opportunity for RSF in the recent past such that there will have been little time to erode smooth the coast. 

 West coast usa is at the edge of a large continent and is a subduction zone rather than a rifting zone ( thus uplifting the continental edge) . Vulcanism on the west coast USA is I think because of the subduction zone rather than a mantle plume which drives Iceland and drove Hebridean vulcanism. Also west USA having been at the edge of a large continental mass for a very long time will have built up a large mass of sedimentary rock which will naturally have a much shallower dip than the Apppalachian Grampian fold mountains and so not give the rock slope failure.

I fully expect someone properly knowledgeable to slay my beautiful hypotheses with ugly facts.

Good question . 

 

In reply to Robert Durran:

Well yes but on a smaller scale, around Mangersta and Aird Uig for example the land rises several hundred feet before ending in cliffs. Same as Foula, Hoy or Handa.

In South Uist the lands slopes gently into the sea with the bedrock some way below the surface.

In reply to Robert Durran:

I'm clutching at straws! Where does the shell-sand come from? I've no idea. Off Ireland? Off ocean beds? Off local rock? In any case, the balance between erosion and deposition could be very delicate, but nevertheless result in a beach in one place and cliffs in another - just small factors favouring deposition/erosion are all that is required to make a massive difference in the landscape.

In reply to Removed User:

I don't think this is the right way of looking at it - the features you describe are only so as a result of pre-existing erosion/deposition processes. (I could be wrong!).

In reply to AndyC:

I'm a Geologist...So is my Wife!!!!

In reply to Robert Durran:

I wonder if you're forgetting about the issue of geological time here. Chossy cliffs may have been more extensive and further out to sea. The rate of erosion will have been faster because of the rock type but we don't see that in our brief snapshot of time. Does that make sense?

 

In reply to Bob Kemp:

Not really, in that I don't think it answers my question!

In reply to Robert Durran:

This is a really interesting question, which I'm struggling to think of a good overall answer to!

I don't have time to do this justice, but I'll throw down some disorganised thoughts:

As others have said, in terms of specifics, it's mostly to do with whether the coast is being protected from rapid erosion, and how elevated it is at the present time.

Deposition, forming sandy beaches, dominates the west coast of Uist and parts of Harris and Lewis. There are two main sources for this sand - offshore carbonate reefs in relatively shallow sections of the sea, and sand brought down by rivers, eroded from hills further inland. Where one of these sources is present, we're seeing beaches form and protect the coast from erosion (with the carbonate sand also blowing inland over low lying peatlands to form machair).

A lot of this is going to come down to the shape of the glaciated landscape formed during and before the last glacial period; this extends below the current sea level. Where it provides a shallow shelf at present, we're more likely to get carbonate reefs and so get sandy beaches. Where it's deeper offshore, it's less likely that the coast will be protected from rapid erosion, so where it has enough elevation we'll get cliffs eating into it.

On Uist, we basically have hills in the east, with a low lying plateau west of them and a fault basin to the east (the Minch Fault) giving deeper water. This low ground continues under the sea and I suppose provides an area where a lot of carbonate reefs can build up; the east coast is steeper and rockier but maybe doesn't form cliffs as readily as it would if it was exposed to Atlantic storms, as the west coast is.

TL/DR - I think a lot of the answer will come down to where the ice sheet was grinding things away, and what shape the land has been left in after (controlling which bits are elevated enough to form cliffs, and equally importantly which areas can form carbonate reefs, plus where larger rivers flow out) - so ultimately determined by the overall flow of ice, by barriers to it (hills), and by weaker, more easily eroded areas (around fault lines, shatter zones, and areas of softer rock). While most of the rock in the Outer Hebrides is Lewisian Gneiss, it's a very varied group of rocks with quite different properties in different areas and a lot of large scale structures cutting through it.

In reply to skog:

Thanks! That all make sense. So basically we should be expecting more cliffs where there is deep water offshore, but fewer cliffs where the sea is shallow? Just need to find some maps of the Hebrides with sea depths shown.........

In reply to Robert Durran:

I think it quite telling that no one has been able to give a simple answer. My copy is in storage so can't check but my usual first place to check for this sort of question is a book I had as an undergraduate - 'Geology And Scenery in Scotland' by John B. Whittow, no doubt long out of print & I can't remember if it had much about the coast. Last time I was "back home" I bought a copy of 'Land of Mountain and Flood' by Alan McKirdy & others but I've yet to read it & I suspect its also  more about the mountains than the coast. But maybe worth a look at

In reply to Robert Durran:

I wasn't really trying to answer your question - it was more a response to the particular point you made about the co-existence of chossy and more solid cliffs, and how rock type didn't have much to do with it if that could happen. I had a look to see if I could get some more insight into this, and found a paper on soft cliff erosion that gave a few rather startling cases, like this:

"On the north shore of Long Island, New York, a hurricane on September 14, 1944 cut back a bluff composed of glacial deposits by a horizontal distance of over 12 m in a single day.9)" 

So soft stuff erodes quickly, and my point was essentially that if there's any left it's because there was a lot to erode in the first place. 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4754505/

This has loads of information on how cliff erosion works - very interesting. 

In reply to Robert Durran:

I -think so-, but it would be interesting to see how this marries up with reality!

In reply to Doug: I imagine as there isn't a single easy answer.  Important factors would be geology, rock hardness, orientation and bedding, but I tihnk more importantly the topography above and below water.  How much of what we see now is wave caused, how much is a result of it being a drowned glacial landscape  (Sealevel has effectively gone up and down), and that in turn affects submarine topography and thus wave effects.

It's not simple!  Comare Harris, Uist to East anglia, the wash and the cliffs on the NE of England. 

 

In reply to Robert Durran:

Link here: http://thebritishgeographer.weebly.com/coasts-of-erosion-and-coasts-of-depo...

In reply to Lusk:

The Channel Islands have raised beaches at 8, 18 and possibly a higher level.  They were formed when se levels were higher. I'd have though the Scottish ones were formed in the same way. They manifest themselves as escarpments inland and layers of beach pebbles wedged high up in gullies and chimneys on the sea cliffs.

Short paper on them here:-

https://www.persee.fr/doc/quate_0004-5500_1982_num_19_1_1413

 

In reply to Robert Durran:

Skog has an explanation for Lewis compared to Uist but also, in general being raised after the formation of the rock in the sea cliffs would presumably normally be necessary? So the flat plain behind the limestone cliffs of Pembroke for example must have been raised - by rebounding after ice melting or plate tectonics movement or local conditions in the mantle? (Speculating wildly)Maybe these were/are also different for Lewis and Uist.

I'm here in Lofoten which is like Harris in that it is dramatically mountainous and near the sea and I haven't seen any sea cliffs.(raises the issue of when is a cliff a seacliff but I think Presten isn't one for example even though it is above the sea). So are there any mountainous regions which also have good seacliffs?  I'm going to stick with the silly explanation that they are too heavy to lift because I like it ( And I'm obviously not a geologist)

In reply to brink:

 

I was thinking just that myself earlier.

I'm struggling to think of any.

Interesting idea.

In reply to Robert Durran:as ever, re. Lofoten, look at what's under the water.  You're seeing the tops of hills carved by glaciers with the valley floor being flooded

 

Edit - define mountainous - there are some excellent seaclffs around Norway , but they are the results of chance flooding, not marine erosion, e.g. Scorpo, an island off the coast at Uskedalen

 

In reply to wbo:

So if Harris is similar, why have cliffs not formed as they have just up the coast on Lewis? If there has not been time since the ice retreated, I would have tought the same would be true of Lewis.

In reply to wbo:

Presumably in Scotland the raised beaches are due to the sea level rising faster than the land rebounding after the ice ages? Lofoten had more ice(?) so presumably is rebounding further - but no sea cliffs. I still think  it's like heavy, man.

In reply to brink:

No, the opposite. Raised beaches are past beaches which are now a fair way above the level of the sea.

 

In reply to brink:

North Wales? Greenland?

 

In reply to Michael Gordon:

Sorry. I didn't explain what I meant well. I meant the sea level must have risen when all the ice melted. So beaches formed. Then the land rebounded and raised the beaches.

In reply to Michael Gordon:

The mountains in North Wales are inland from Hogarth and the Lleyn.

I just checked & the book 'Land of mountain & flood' which I mentioned earlier does have a few pages on coastlines & seacliffs. But although it describes some examples the overall message is that the coast at any given point is a result of the interplay of geology, glacial history & hydrodynamics

 

In reply to Michael Gordon:

I think, like Norway, flooded glacial valleys rather than sea eroded cliffs.

 

 

In reply to brink:

The beaches pre-date this non-glaciated period we're currently in. When the ice left and the land rose (iso-static uplift) they gradually became raised beaches. 

In reply to Michael Gordon:

Thanks, I stand corrected.

In reply to Robert Durran:

It's an interesting question. I guess it depends how near the mountains have to be to the sea for it to count as a 'mountainous area', and how mountainous something has to be to be called a mountain! I'm trying, and failing, to think of mountains which pretty much rise up straight from the sea, which of course would entail a huge altitude differential within a short space, and for that reason alone perhaps makes it an unlikely occurence.   

In reply to Robert Durran:

Try the pdf linked from here...

https://www.nature.scot/landscape-fashioned-geology-outer-hebrides

 

In reply to Michael Gordon:

Maybe there is somewhere a recent volcano rose in the sea and then got seacliffs round it? Iceland seems a possible but I guess that would be a different mechanism to the one we're trying to explain

In reply to Michael Gordon:

The Rivals,  Llyn peninsula?

In reply to Michael Gordon:

Maybe St Kilda ? (not been there so based on photos). I've also memories (but from long ago) of a large cliff in Lofoten which although not quite a sea cliff, started from the beach.

In reply to baron:

Faroe Islands? Hawaii?

In reply to Michael Gordon:

Hawaii, or closer to home;  Croaghaun and Sliabh Liag.

In reply to Michael Gordon:

Easy. Much of the west coasts of Scotland and Norway. There just don't seem to be places where the bottom of these mountains have eroded into sea cliffs.

 

In reply to Robert Durran:

Yes, I guess I meant steep mountains rather than hills, with cliffs on them which start from, or below, sea level.

In reply to Doug:

I'm not sure I'd say St Kilda has mountains on it (An Dun has a great-looking knife-edge ridge though).

I thought Lofoten likely, and was surprised given it's maritime nature that others report it as lacking sea cliffs (I've never been).

In reply to Robert Durran:

A bit late to this thread, but here's a bit more detail on the Outer Isles...

In very general terms you need two things for sea cliff formation: bedrock that is tough enough to support near-vertical slopes, and a sufficiently high-energy wave environment (relative to the strength of the bedrock) to erode/undercut the coastline and lead to scarp formation. In reality it’s much more complex than this, so it’s easy to think of places where the landscapes are varied, despite seemingly uniform geology and erosion. The Outer Hebrides are an excellent example and skog’s post has identified several of the main factors. I’ll try to expand on them here.

The vast majority of the Outer Isles are made up of Lewisian Gneiss. As well as being one of the finest rock types you’ll ever climb on, these gneisses are pretty remarkable – not least because they range in age between about 3.2 and 1.5 billion years old. This makes them the oldest rocks in Britain and among the oldest visible anywhere at the surface of the Earth. Picking out geological details this far back in time is difficult, so rock classifications like “Lewisian” are pretty coarse: it's a term that covers more than 1.5 billion years of geological activity, after all, and since they formed they’ve been through another 1.5 billion years of folding, faulting and erosion. This means that, although you’re correct to say the Outer Isles are, “all the same rock type”, there’s nevertheless a huge amount of compositional and structural variation.

From the point of view of composition, the Lewisian of South Harris consists of metamorphosed gabbros, sediments and assorted bits of old continental margin. On North Harris and Lewis, the “parent” rocks were more granitic, but in the south (North Harris and the southern half of Lewis), some them actually melted during metamorphism to form pink granites and pegmatites (now the Uig hills). The northern half of Lewis experienced less of this melting, so the rocks there are a bit less differentiated.

In terms of geological structures, the last main phase of the Lewisian metamorphism created several huge, linear shear zones, which correlate very clearly with major features of the present-day coastline. These shear zones help to define the straight and craggy northwest coast of Lewis, and the cliffs around the Butt of Lewis itself. There are also many more recent faults running roughly SE-NW, especially across Harris and the southern half of Lewis. In combination with the bedrock contrasts described above, these faults have been exploited by subsequent river and glacial erosion to determine the locations of major inlets and bays (e.g. Loch Roag, Uig).

Finally, the Outer Isles are located on a large, sloping platform that is highest in the east (along the Minch Fault, as stated by skog), and tilts gently westwards to the edge of the continental shelf just beyond St. Kilda. This shelf is a bit broader and shallower offshore from the Uists than it is off Lewis, which may mean Lewis is more exposed to high energy waves than the islands to the south. This platform is also the source of the carbonate-rich sediments forming the Outer Isles’ distinctive white beaches, which is why the machair is more extensive on the Uists than further to the north.

In summary, as Doug said, sea cliff formation is a complicated combination of bedrock geology and erosion/geomorphology. It's also important to bear in mind that even within a single geological unit you can still find structural and compositional contrasts to account for significant landscape variation.

In reply to Lusk:

Confirmed

 

In reply to Sammo:

Thanks! A great supplement to the geological section in the new guidebook.

In reply to Robert Durran:

It would take a decent A level Geographer about 4 sides of A4  to do justice to your question but to summarise 

Wave action: Some waves are said to be constructive and have a strong upward motion called its Swash these will bring material onto the beach and not cause much erosion but deposit material on the shore. Other areas will have destructive waves with a strong Backwash down the beach, these will create steep undercut cliffs. The angle of slope of the beach down to the sea will influence the type of wave amongst other things. The material removed from the Channel Tunnel was dumped on the beach under parts the of the White Cliffs, changing the beach profile, much less undercutting, less rock falls from above, now cliffs have vegetation  and are more green than white at this location. 

Isostatic Re-adjustment: As several posters have said the North West of Scotland is rising at a measurable rate while the South East of England is sinking.The weight of ice removed from the Scottish Highlands has allowed the land to rise. There is, as a result, a raised beach  round much of The Isle of Arran, the coast road uses it for many miles. If you know the village of Pirnmill in the north of the Island then it's located on one of a series of raised beaches. If you look into the back gardens you can see an ancient cliff line complete with caves and in one garden even a natural arch some 15-20 metres above present sea level.

On top of this you would need to consider "length of fetch" and wind direction and geology to name but a few. It would probably be best to consider each shore line and try to decide what's happening there. 

Now watch the blackboard while I go through it again.

In reply to Robert Durran:

That's a good account from Sammo, agree with much of what was said. The original question is actually quite hard to answer (speaking as a professional geologist, but with amateur interests outside my discipline) due to all the many influences at work on scenery.

 

I believe it is best to work backwards in time looking for reasons, e.g. current wave/tidal action, then post-glacial rebound and glacial effects, then Tertiary North Atlantic inversion and volcanism, then the orogenic phases (Caledonian) preceding that, then the original age of the rocks themselves and the metamorphism and remobilisation Sammo has described.

 

The Minches and outer isles have been heavily affected by relatively recent large scale faulting and reactivation and the dips Sammo describe have an impact. The Great Glen fault has endured repeated reactivation that has affected the Moray coast.

 

A few comments: Sea cliffs form where net erosion is greater than net deposition and where resistant rocks remain from earlier uplift, or are uplifted by late inversion or isostatic uplift, e.g. glacial rebound or Alpine inversion.

 

For example, Morecambe Bay was uplifted 7-10,000 feet during the Tertiary, hence plenty of sea cliffs at St Bees, Anglesey etc. Scotland, Scandinavia etc are rising due to post-glacial rebound.

 

Non-resistant rocks get eroded and destroyed by the sea, so much of the Lancashire coast, East Yorkshire coast are without cliffs and sites of either severe erosion or net sediment deposition with extensive beaches or sand flats, sometimes enhanced by tidal estuaries like the Humber, Mersey or the Solway.

 

Looking at the geological map of UK and the Geological time scale, it seems all ages of rocks can form cliffs, so we have Pre-Cambrian, Cambrian, Ordovician, Silurian cliffs e.g. Isle of Man, Western Scotland, Durness, Aberdeen shire, Southern Scotland etc.

 

We have Devonian and Carboniferous cliffs at Duncansby north east Scotland, Orkney, Devon/Cornwall, South Wales, Orme, some around Morecambe Bay.

 

Permian and Triassic cliffs in Durham, St Bees, Fife. Jurassic cliffs in Dorset, North Yorkshire, Raasay and Brora. Cretaceous Chalk cliffs are extensive in Sussex, Kent and East Yorkshire - relatively soft rock but much harder than the adjacent rocks and subject to late inversion around the Weald, Dorset, Market Weighton axis in Yorkshire etc.

 

Tertiary and later (glacial) cliffs are universally soft and under erosion in Hampshire and East Yorkshire, except when they are volcanic as in Northern Island or Western Scotland.

 

Intrusive granites etc and other volcanics usually form cliffs as they are harder than the country rock - Cornwall, West Scotland etc.

 

It is still a hard question to answer nevertheless. There has been a huge amount of up and down, especially recently due to the Alpine Orogeny and the North Atlantic volcanic and spreading related uplift, e.g. Carthage, Santorini under water, plus the complex ice age effects.

 

DC

 

 

In reply to Robert Durran:

Have you spoken to the geography department Robert?  

In reply to DaveHK:

I could do, but I'm pretty sure I wouldn't get a better reply than some of the excellent ones on here!