Author Topic: Vertical range of a sea cave, and just when does an alcove become a cave anyway?  (Read 3503 times)

Offline tarquinwj

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Intro; I maintain a list of the longest and deepest caves in the British Isles. I am struggling with one potential "cave".

When it comes to vertical range of a regular cave, it's relatively easy. Change in altitude between the highest point and the lowest point, sump or dry. If the highest point is the roof of a chamber, then so be it.  :thumbsup:

When a regular cave entrance is huge, breaking out of a cliff face, it's possible that the highest point is the top of the entrance arch (imagine the Grotte de Bournillon's entrance). The highest point that belongs to the cave is used. If the cliff overhangs a long way above a cave entrance, the cave's vertical range does not extend all the way up to that overhang. We're interested in the cave's vertical range here, not the cliff.

So now to the problem; sea caves. There are submerged caves (eg. Mermaid's Hole), there are tidal caves (eg. Otter Hole), and there are wave action sea caves (eg. Sandside Head Cave No. 2). The last type is the difficult one. Sometimes they form blowholes, and the vertical range of those is as easy as a regular pothole. In fact, this gives us the deepest known sea cave in the British Isles; 79 metres, Devil's Limekiln,  Lundy Island :thumbsup: Sometimes they are taller inside than at the entrance, due to an arched ceiling, and that's easy again.  :thumbsup: Sometimes the entrance arch is the tallest part, but it's obvious where it starts (eg. Halvikshulen in Norway, at about 80 metres).  :thumbsup:

But then there's the case where the entrance just keeps curving upwards until it merges into the cliff. Since the cave and the cliff are formed by the same process, there's no obvious point to say where the cave ends, and where the cliff begins.  So what is the vertical range? :-\

This comes from a real example, which has the potential to knock Devil's Limekiln off the top spot; the immense alcove in Stookeen Cliff at the Cliffs of Moher, Co. Clare, Ireland. (The one used in Harry Potter and the Half Blood Prince, if that helps.)

By my calculations, the point where it gets a slightly undercutting flat ceiling for the first time is about 95 metres up. But is that really the point where cliff becomes "cave"? Note that the walls extend beyond the upper cliff face, so they can't be used to define a start position.
So is this a cave with 95 metres of vertical range?

And that prompts the next question; does it even deserve to be a "cave" at all? It's an alcove about 40 metres deep. That's less than the height of the opening. Can it really be a cave when it does not even extend into the cliff as far as its own height? Sure, we call it a sea cave, but does it really deserve to compete with Devil's Limekiln, or the likes of Eldon Hole, Sunset Hole and Bull Pot? :unsure:

Sorry for the academics, but I want the opinion of others here. It's not fair for me to redefine things without the feedback of others.

Offline mrodoc

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If somebody has called it a cave its a cave :smartass:

Offline graham

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In the absence of agreed definitions of what constitutes a 'cave' one can only have opinions. Mine is that the alcove described ain't really a cave in my book. Been to Moher many times, never heard that name before, thanks.  :thumbsup:

A similar example can be found in France - except that I cannot remember what it's called.  :-\ The second (or third) largest cave entrance in France is really just a very shallow scoop in the cliff, with a quite low (~ 2 m ) cave going off from the back at the base. When we there, the general consensus was that the statistic was, really, taking the piss.

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Offline Rob

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I don't personally have a strong opinion about this, however i know this is a challenge that you are not facing alone.

The UIS has recently setup a commission to try to get some "rules and regulations" for numerically defining caves. This is no small feat, especially when you take into account all the different types of caves around the world...

I think it's all going to end up as a long set of rules backed up by a lot of maths and equations!!!
The end is where we start....

Offline bograt

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Most dictionaries define a cave along the lines of ; "A hollow or natural passage under or into the earth".
 This instance is barely a hollow and is certainly not a passage so I would describe it as an alcove or rock shelter, not a cave. I would suggest that a cave should go in further than the height of its entrance.
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Offline Fulk

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Is a passage a cave if it's not big enough for an (average-sized) person to get into? (Errrr . . . does it matter?)

Offline TheBitterEnd

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I can't remember where I read it but I think it was one of the standard text books (Palmer? may be others) that defined a cave as anything large enough to be entered by a person.
'Never argue with a fool, onlookers may not be able to tell the difference.' — Mark Twain

Online topcat

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I would suggest that a cave should go in further than the height of its entrance.

I agree, and it would be simple to decide based on this.

Offline Rob

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I would suggest that a cave should go in further than the height of its entrance.
I agree, and it would be simple to decide based on this.
...apart from this topic started with trying to determine the height of an entrance!
The end is where we start....

Offline Bottlebank

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I would suggest that a cave should go in further than the height of its entrance.

I agree, and it would be simple to decide based on this.

Just to cement my new found reputation for awkwardness, where would this leave Jingling Hole in Kingsdale, for example  :-\

I prefer the anything big enough to swallow a person idea.
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Offline TheBitterEnd

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...  where would this leave Jingling Hole in Kingsdale, for example  :-\

Ahh! but that's a pothole, not a cave  ...   [runs for cover]
'Never argue with a fool, onlookers may not be able to tell the difference.' — Mark Twain

Offline tarquinwj

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Thanks all for the replies, you've been most helpful. :) It seems at least that there is some agreement that the cave needs to be more than just an alcove (ie. longer than its entrance height) in order to qualify.

where would this leave Jingling Hole in Kingsdale, for example  :-\

That formed entirely as a cave formation process, so it's fairly easy to work out what is "cave" and "not cave"; as cavers, we have managed to interpret that fairly well for ourselves in most cases. In the case of a sea cave, it becomes much more difficult, since the same process forms both the cliff and the cave. There has to be some point at which it stops just undercutting a cliff, and starts punching out what we will come to call a "cave".

There are some other examples around the Mayo coast that I have been told about, such as on the west side of Benwee Geevraun Point (near Belderg/Belderrig), 54°19'10.18"N 9°34'58.47"W. Here, the cliffs are 150 metres high, vertical for about the bottom 100 metres, and overhanging for the bottom 50-60 metres, by about 10 metres or so. At the bottom are some cave entrances, but the overhang could potentially also be considered to be part of the cave. Photos below.

It is my personal opinion that the cave is what sits at the bottom of the alcove, not including the alcove. As graham said; including the overhanging cliff as well, would basically be stretching the definition too far. That is; unless the alcove's depth is a significant fraction of its height (eg. 50%), it doesn't deserve to be included, even if there is a long cave starting inside the alcove.


Roughly; a 60 metre high alcove extending 15 metres into the cliff, with a 10 metre high, 300 metre long cave starting at the back of the alcove. I would say the cave has a vertical range of 10 metres and a length of 300 metres. I would not say the cave has a vertical range of 60 metres, and a length of 315 metres. It does not deserve to have the alcove included in the cave's measurement, imo.

[Edit] This image shows the alcoves at least (the two on the left)

this shows the relatively tiny cave entrance at the bottom of the righthand one
« Last Edit: October 23, 2013, 04:35:01 pm by tarquinwj »

Offline Fulk

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Quote
That formed entirely as a cave formation process, so it's fairly easy to work out what is "cave" and "not cave"; as cavers, we have managed to interpret that fairly well for ourselves in most cases. In the case of a sea cave, it becomes much more difficult, since the same process forms both the cliff and the cave.

Just to put in for this week's pedant's award, I'd point out that in the case of Karst scenery, the same processes (corrasion and corrosion of limestone) result in both cliffs and caves.  :smartass:

Offline bograt

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Surely a cave doesn't start until its got four sides :-\,
So measurement should start when you've got walls as well as top and bottom?
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Offline graham

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Surely a cave doesn't start until its got four sides :-\

Five.
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Offline bograt

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Surely a cave doesn't start until its got four sides :-\

Five.

 :lol: :lol: Depends on if its a "goer" :)
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Offline tarquinwj

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Surely a cave doesn't start until its got four sides :-\
Is Sótano de las Golondrinas measured from its upper or lower lip?  :shrug:

A pothole situated in a wide shakehole has four walls for some distance above its entrance (eg. Lamb Pot, in the Marbe Steps swallow hole), but the depth is most usually measured from the entrance to the cave, not the rim of the shakehole - this varies of course, depending on how much the shakehole feels like part of the cave, and depending on what mood the surveyor is in. Again, I'd point to Lamb Pot. The width of a shakehole is not considered to be part of the cave length either, even in the cases where the surveyor randomly decides to add the depth of a shakehole onto the depth of a cave.

Tell you what, I'll take it to an extreme. Imagine a cave situated in a blind dry valley, very wide indeed compared with the cave opening. Would the cave depth be the depth measured from the opening inside that valley, or the rim of the valley itself? Extreme case, a cave situated on the shore of the Dead Sea, entrance at -423 metres, depth of 200 metres. The lip of the Jordan Rift Valley is at 230 metres (Arabah valley near Paran, just so you know). We would say the cave is 200 metres deep, not 200+423+230 = 853 metres, even though for those 653 metres above the entrance, it actually has got 4 "walls", so to speak.

Think that may be the best way to picture this; those alcoves containing caves are just like the valley that contains a pothole. They exist, but they are not part of the cave formation. At least until they become indented into the cave more significantly than a shakehole is indented into a pothole.

Offline Rob

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Yup, it's a tricky job!

From where would the depth of Houping Tiankeng be measured?


The lowest part of it's top rim? But there's trees and "flat" floor below there!
The end is where we start....

Offline glyders

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My feeling would be that it is a cave if the distance that can be progressed by a person into it is greater than the dimensions of the entrance. I am trying to be as general as possible to cover horizontal caves and vertical pots.
I also feel there ought to be something to do with there being places daylight never reaches but I can't define it to my satisfaction.

Offline bograt

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I thought the original query was about caves, potholes is different :shrug: :shrug:
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Offline tarquinwj

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I thought the original query was about caves, potholes is different :shrug: :shrug:
Essentially, it is about both. Sea caves come in both the basic "cave" variety, and the pothole (blowhole) variety. Both need to be accounted for, since any list of "deepest caves" has to take into account both mainly-horizontal caves and mainly-vertical caves, since either can have very significant vertical range (the deepest cave in the UK is, after all, a cave, not a pothole). A general rule which applies to both is nice to have (rules don't really exist, since it's up to the surveyors what place they personally choose to be "the cave", but I try to imagine a perfect world). It allows me to discount silly cases where exaggerated claims are made in an attempt to boost a cave beyond its deserved rankings. Bear in mind that very few sea caves are properly surveyed, so I do have to work with a lot of hearsay and very poor estimates ("it was about 200 paddle strokes, so that's 200 metres long").

The difficulty comes mostly from the horizontal variety of sea caves, and working out where the highest points within that cave are. Is it the top of the entrance passage's arch, the highest point of the inner passage, the top of the overhanging cliff above the cave or alcove containing it, etc.
The consensus here seems to be that a large alcove or cliff overhang around the entrance is not to be counted, since it does not extend inwards at that size far enough to be counted as actual cave passage.

As graham stated, "one can only have opinions", so I am most grateful for the feedback here from all of you :)

Offline NigelF

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There is a similar problem when it comes to natural arches v seacaves.
There are a number of seacaves with a hole near the entrance such that one could call it an arch followed by a cave, or say it is one cave with a smaller or a larger hole.
There is an arch system - Folga Skerry (1) on the W side of Papa Stour - which has a length of 250 m given to it - so I think it is probably right to have it in both categories.
And, of course, many natural arches were seacaves in the more easily recognised sense at some time in the past.
The 1st Ed OS shows a two tunnel system under Brei Holm (E side of Papa Stour). But now their is a large pot or gloup roughly where the join probably was, and what was the shorter tunnel is "obviously" an arch.