Vertical range of a sea cave, and just when does an alcove become a cave anyway?

[tarquinwj]

I thought the original query was about caves, potholes is different

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

 

[NigelF]

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.