How long is that cave-Really?!

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How long is that cave-Really?!

Postby trogman » Aug 8, 2009 12:05 pm

I looked in vain through this Forum for anything on this topic, so I will introduce it myself. I have been finding and turning in new caves for several years, all of them have been in either AL or GA, and I have asked this question of several surveyors/cartographers. I keep getting different answers, so I thought I would throw it out here and see what the folks on Cavechat thought about it. My question is regarding the "length" of a cave that is stated on a map and/or in the state survey listing. I have the "On Station" book, and in it George Dasher states that the "length" of a cave is the total passage, whether it be horizontal, vertical, or something in between, that a person would pass through to go through the entire cave. This makes sense to me. But many folks I know take the length of horizontal passage (anything that is not a vertical pit), and put that down as the "length" of the cave. So a cave that has a 50' pit with 90' of passage at the bottom is stated as being a 90' long cave with 1 pit 50' deep. Likewise, a blind bottom pit 50' deep would be reported as a cave with 0' of passage and a 50' pit. Then of course there is the "map length," which if I understand correctly, is the plan view length of passage. If these “lengths” are not clearly specified or understood, it can get pretty confusing.

I guess what I am looking for here more than anything is some sort of "official" standard method that most cavers and state surveys can agree to. That way, we could compare apples to apples. I know that's asking for a lot-maybe I'll bring this up at the next ACS meeting. What do you all think?
Thanks.
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Re: How long is that cave-Really?!

Postby ian mckenzie » Aug 9, 2009 10:46 pm

trogman wrote:the "length" of a cave is the total passage, whether it be horizontal, vertical, or something in between, that a person would pass through to go through the entire cave.
Yup.

trogman wrote: But many folks I know take the length of horizontal passage (anything that is not a vertical pit), and put that down as the "length" of the cave. So a cave that has a 50' pit with 90' of passage at the bottom is stated as being a 90' long cave with 1 pit 50' deep. Likewise, a blind bottom pit 50' deep would be reported as a cave with 0' of passage and a 50' pit.
Nope.

trogman wrote:Then of course there is the "map length," which if I understand correctly, is the plan view length of passage.
Nope.

Real problem is when survey shots that do not measure passage length are included e.g. measurement of passage width, room circumferences etc. There is no real concensus on those sort of things, some think they are valid to include while others do not.
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Re: How long is that cave-Really?!

Postby Bob Thrun » Aug 19, 2009 5:37 pm

If two survey stations in a cave are 100 feet apart, then that section of cave passage is 100 feet long, whether it is horizontal, sloping, or vertical. I have a hard time arguing with the numbers on a tape.

I had an article on the subject in Compass & Tape, Vol. 9, No.1,2, which came out in February 1992. I looked thru Speleo Digests to see how cave length was reported, In 1969 C.D. Ritter used the term "True Horizontal Cave" on two maps and "THC" on two others. All were for Indiana caves. Also in 1969, Ron Zawislak used "True Horizontal Cave" for a Tennessee cave. These were the first uses of these terms that I found. To this day these terms continue to be used on maps of Indiana caves. I object to them because of the word "True", which implies that other measures of length are false.

The most commonly used term was "Length", followed by "Surveyed Length".

Many maps did not have any length stated on them. In the 1964 Speleo Digest, only one map had the length on it. In 1965 there were none. The maps in Caverns if West Virginia and Caves of Tennessee do not have any length on them. If you want to get the length of a cave when there is no length stated on the map, there is little alternative to measuring the plan length on a map. Of course you should realize that most of the maps in Caverns of West Virginia are pace and compass.
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Re: How long is that cave-Really?!

Postby wyandottecaver » Aug 19, 2009 6:19 pm

Interesting. 99% of my cave map experiance is in Indiana. Thus I assumed the THC (horizontal) and TVE (vertical) was a semi standard rather than a regional quirk. Though I had heard it used as total horizontal control and total vertical extent. I have also seen Survey Length used a lot.

I have not noticed a scheme for listing vertical lengths seperate i.e. 4 different 50' pits giving 200' of vertical cave. Rather the depth from highest to lowest point in the cave listed as its total depth regardless of how many vertical feet of pits/domes there may be.
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Re: How long is that cave-Really?!

Postby trogman » Aug 20, 2009 9:33 am

wyandottecaver wrote:I have not noticed a scheme for listing vertical lengths seperate i.e. 4 different 50' pits giving 200' of vertical cave. Rather the depth from highest to lowest point in the cave listed as its total depth regardless of how many vertical feet of pits/domes there may be.


That wasn't exactly what I meant-no, I haven't seen that either. I will usually list the Vertical Extent separately, and calculate it just as you stated above.
What I have seen is many caves turned in as having "0" feet of length, or maybe 5 or 10 feet or so, and then the pit depth listed separately. With this system, a cave is turned in as, say, 10' long with a 20' pit. In the state of GA, that will qualify as a cave, but in AL it won't.(because it adds up to 30'; AL requires 50') I guess my main question was having to do with the "length of cave," which I will usually put in the title box of my map. What I am getting from the some of the above replies is that many do not even state the length on their maps, or if they do, it is the length of the map or plan view, and not the actual surveyed length. I almost always list the Vertical Extent and # of pits on a map, along with the depth of these pits. I will usually list the Vertical Extent separately, and calculate it just as you stated above.

Does that make sense?

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Re: How long is that cave-Really?!

Postby tncaver » Aug 20, 2009 11:30 am

It would seem that a pit has some amount of horizontal length to it whether it is a blind pit or not and should be included in the
total horizontal extent of a cave.
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Re: How long is that cave-Really?!

Postby Chris Chenier » Aug 20, 2009 12:36 pm

Horizontal length can easily be measured (or verified) on a plan view of a cave, but other than that, I don't see a use for it other than perhaps for some geomorphological study where horizontality would be more important. I think that accounting horizontal length only comes from either surveys that were done without clinos (mostly in the old days, but I hear some are still doing this) and/or caves that are mostly horizontal, where it wouldn't make much difference which one you used, and/or surveys being reduced without a computer (old, again).

If Alabama requires 50' for a cave to appear in the state cave survey, and we were to use the horizontal length, that would mean that a 500' free drop with nothing at the bottom would not be considered a cave... hardly logical.

Total length traveled makes a lot of sense to cavers (and scientists) as this is a good representation of how much passages there are. This is what is being used in all projects I've been involved in. That being said, I know there are a lot of surveys stating total horizontal distance, but I'm still waiting to hear a logical explanation for using this. Is there any argument other than historical for using this method?

I don't include splay shots (side shots) and if I survey around a room, then only half of the legs get counted. This is done because it is rather arbitrary how many splays to use and how big a room needs to be before you start surveying all around it. Length at junctions can also be confusing: should the width of the "main" passage be included in the length of the "side" passage? Also, do you include all those 2 meter long side passages? Only if you actually measure them or even if you just sketch them? With all these variables, it's not surprising that cave lengths quickly becomes quite a subjective measure. I've experimented some years ago on the survey of a rather irregular-shaped cave (lots of junctions, very irregular wall with nooks and crannies everywhere, etc...) and found that it was very easy, at least in that case, to add or substract as much as 20% to the cave length depending on where you take shots and what constitutes a "significant" side-passage. There was an article a year or two ago by Pat Kambesis (I think it was in Compass & Tape) on how to "measure" flank margin caves. This is a good example of the problem found with "irregular" caves.

Length is of course just one metric that can be used to size a cave; depth is also very common. Others would be floor area and volume.
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Re: How long is that cave-Really?!

Postby trogman » Aug 22, 2009 9:02 am

Chris Chenier wrote:If Alabama requires 50' for a cave to appear in the state cave survey, and we were to use the horizontal length, that would mean that a 500' free drop with nothing at the bottom would not be considered a cave... hardly logical.

Perhaps I was not totally clear about how the ACS handles this. As far as I understand it, they take the combined length of surveyed horizontal cave, and add it the depth of the drops to determine if it meets the 50' length requirement. By "horizontal cave," I don't mean THC, but rather any passage measured which is not a vertical pit. By "depth of drops," I am referring to the depth of each pit, and not the vertical extent. So the hypothetical 500' deep pit with no passage at the bottom would still qualify 10 times over. (it is hypothetical, isn't it? :tonguecheek: )

I surveyed a cave recently which had 2 entrances, the first being a climbdown into a small entrance room, and the 2nd being a hole/skylight that dropped directly into the entrance room. It measured out at 13’ deep. While I did include the 2nd entrance in my report, I did not add the 13' to the total length of the cave. I'm not entirely sure if I should have or not, but since it wasn't actually a separate passage, I decided not to.

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Re: How long is that cave-Really?!

Postby George Dasher » Aug 28, 2009 10:18 am

You all are making this way too difficult.

Bob Thrun is correct; you can't argue with the survey tape.

If the tape says the cave is 100 feet long, then the cave is 100 feet long, no matter what the slope of the tape.

Thus a vertical 100-foot-deep, dead-bottomed pit is a cave 100 feet long.

Another example would be holding up a yard stick at many different angles. The yard stick is still one yard long, no matter what angle it is held out.

Thinking horizontal distance for a cave length only confuses the issue. It is best just to mentally delete horizontal length from the entire process. It doesn't count for anything.

And there is an offical document for this. It was described in the January 1981 NSS Bulletin.

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Re: How long is that cave-Really?!

Postby tncaver » Aug 28, 2009 10:43 am

George Dasher wrote:You all are making this way too difficult.

Bob Thrun is correct; you can't argue with the survey tape.

If the tape says the cave is 100 feet long, then the cave is 100 feet long, no matter what the slope of the tape.

Thus a vertical 100-foot-deep, dead-bottomed pit is a cave 100 feet long.


Tennessee Cave Survey is different. A 100 foot pit with 20 feet of passage (or 20 feet in diameter for example) would
be listed as being a 100 foot deep pit with 20 feet of horizontal extent. I am thinking that the horizontal length for a
sloping passage is figured using the angle to determine the actual horizontal extent as opposed to the measured distance.
For mapping purposes, this is more accurate.

Why do this? For example: If someone wanted to dig a new entrance to a cave, and that cave has numerous sloping passages
and pits, it would be necessary to know the actual horizontal distance from point A to point B. Otherwise, the dig could miss the intended cave passage completely. The exact horizontal distance from point A to point B in the cave can only be determined by surveying and calculating the degrees of all slopes to acquire actual distance. The same thing would have to be done on the surface for an entrance dig to hit the cave in the right spot. Of course, using a cave radio locator can provide the same result without surveying at all. Any TCS members want to chime in?
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Re: How long is that cave-Really?!

Postby Jeff Bartlett » Aug 28, 2009 10:47 am

George Dasher wrote:You all are making this way too difficult.

George is right. If some cave surveys choose to include an additional figure with a different meaning, like "horizontal extent," that's fine. But the cave's length is the cave's length.
"Although it pains me to say it, in this case Jeff is right. Plan accordingly." --Andy Armstrong
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Re: How long is that cave-Really?!

Postby George Dasher » Aug 28, 2009 11:19 am

For mapping purposes, this is more accurate.


No, it is not. "Horizontal length" is much less accurate, and it only complicates things.

Once again: You can't argue with the survey tape.
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Re: How long is that cave-Really?!

Postby tncaver » Aug 28, 2009 12:46 pm

George Dasher is an expert cave mapper. I am not. There is no way I am going to dispute his statement. I am including a simple image to illustrate my point. I think I must have done a poor job explaining what I meant, so I hope this illustration will
demonstrate what I was trying to say.

Image
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Re: How long is that cave-Really?!

Postby George Dasher » Aug 28, 2009 2:18 pm

Well, I am confused--because I no longer understand what we are "arguing about."

Certainly, when doing a dig (and making three sides of a mathematical triangle to "hit the cave passage"), you're going to have to take slope and horizontal distance into account.

But I thought we were discussing cave length, and--in which case--I'm sticking to my guns. The length of the cave is the sum of its slope lengths. It is not the sum of the horizontal lengths, as these are a projection of the slope lengths.

Maybe I got side tracked in my previous post, but I was talking about cave length.
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Re: How long is that cave-Really?!

Postby tncaver » Aug 28, 2009 2:24 pm

Sorry, I think I created the confusion because of my misuse of terminology.
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