Easier ways to discover new cave passages!!!
- Thread starter axbridgecaver
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andymorgan
Guest
Surely it can't be that hard to do a resistivity survey over a known cave and compare the results of the actual survey, to see if the technique works or not :?:
graham
New member
Ouan said:
It does not show conclusively that the method works, it shows that if you know what the result should be, you can (knowingly or otherwise) manipulate the data to agree with that result. I am not aware, as yet, of anyone discovering a previously unknown void (aka a "cave") by this method and then entering it. That would be the only useful demonstration that the method works.
AndyF
New member
Ouan said:
The problem is that results need "interpretation" in the way that only the human mind can in order to draw conclusions. It can be very subtle. If the "correct" answer is known, it tends to lead the user to point out where there is correlation, and ignore things that don't fit. A bit like Millikans famous oil drop experiment: know the result, dismiss the bits that don't match...
The only true test is a predictive one, followed by proof by exploration (this applies too for dowsing too!) This is why I'm interested in the Lamb Leer measurements, it seems to off an opportunity for a valid test...
Rob
Well-known member
These days cave discovories are few and far between, and those that are found are probably on average getting deeper. The chances of somebody actually predicting where a cave "should" exist and then digging into a large void there is fair to pretty slim. The chances of someone beforehand doing a resistivity (or similar) reading on that area is even less. We could be waiting years, decades, before this is ever acheived.
The techniques being discussed, potentially, could be superb tools in aiding us find new cave. The only thing stopping people is that everybody is disagree about whether they work well or not. All that needs to be done is they need to be tested. To test if these techniques work is not to look in hope and vain, but to just do readings above known cave, and for it all to be done by people who don't know where the cave is, organised a little at the start by people who do. If they find it then it works!
Why has nobody done this yet, or if they have, where are the results? This is all that is need to end this discussion and to let us carry on digging!
The techniques being discussed, potentially, could be superb tools in aiding us find new cave. The only thing stopping people is that everybody is disagree about whether they work well or not. All that needs to be done is they need to be tested. To test if these techniques work is not to look in hope and vain, but to just do readings above known cave, and for it all to be done by people who don't know where the cave is, organised a little at the start by people who do. If they find it then it works!
Why has nobody done this yet, or if they have, where are the results? This is all that is need to end this discussion and to let us carry on digging!
Ed W
Member
I have been popping in to this board occasionally for a long time, but finally I have found a thread that has prompted me to post. I have been involved in using geophysics to "find" caves, but must point out that I am not a geophysicist (though I did work with some many years ago in the oil industry).
Unfortunately I cannot provide an example of a cave being entered after being "discovered" by geophysics, but I can give an example that comes pretty close. The work was carried out on the Laki Underground Expeditions (Iceland) in 2000 and 2001. Various geophysical techniques (magnetometry, resistivity and ground penetrating radar) were used over the up flow end of a lava tube cave called Stefanshellir. At the upflow limit is a short section of very large tube leading from a collapse entrance that suddenly ends at a complete lava seal.
The cave was very accurately surveyed (I seem to recall a station every 2m) and tied into a surface grid using differential GPS. the geophysical instruments were then used following this grid which had been accurately positioned with respect to the cave beneath (though the grid extended some distance beyond the known cave in all directions). The results are pretty unequivocal, the geophysical anomalies tie in excatly to the cave survey.
After the initial proving of the technique, the survey was extended up the lava flow, and appearsto show tha the lava seal is some 20m long and then a large cave passage continues for at leat 400m. The Icelandic Speleological Society were well enough convinced to start arranging for a drilling operation to enter the cave, but unfortunately a spate of politics has broken out which has put paid to this.
But, for some of the posters here I would suggest having a look at the expedition report (published by Bournemouth Uni, authored by Dr Chris Wood and available from Amazon or some caving club libraries) which contains plots of the raw data from the experiments. Even to a non-geophysicist the results are very clear indeed. There are a couple of poor quality pictures in the Shepton Mallet Caving Club Journal Series 10 No.10 as well which may be easier to get hold of.
I do need to point out however that conditions were almost perfect, flat surface topography with large passages only a few metres down. Also the magnetic technique which proved the most use is probably completely useless in Limestone caves.
Hope this is of interest in the debate,
Ed
Unfortunately I cannot provide an example of a cave being entered after being "discovered" by geophysics, but I can give an example that comes pretty close. The work was carried out on the Laki Underground Expeditions (Iceland) in 2000 and 2001. Various geophysical techniques (magnetometry, resistivity and ground penetrating radar) were used over the up flow end of a lava tube cave called Stefanshellir. At the upflow limit is a short section of very large tube leading from a collapse entrance that suddenly ends at a complete lava seal.
The cave was very accurately surveyed (I seem to recall a station every 2m) and tied into a surface grid using differential GPS. the geophysical instruments were then used following this grid which had been accurately positioned with respect to the cave beneath (though the grid extended some distance beyond the known cave in all directions). The results are pretty unequivocal, the geophysical anomalies tie in excatly to the cave survey.
After the initial proving of the technique, the survey was extended up the lava flow, and appearsto show tha the lava seal is some 20m long and then a large cave passage continues for at leat 400m. The Icelandic Speleological Society were well enough convinced to start arranging for a drilling operation to enter the cave, but unfortunately a spate of politics has broken out which has put paid to this.
But, for some of the posters here I would suggest having a look at the expedition report (published by Bournemouth Uni, authored by Dr Chris Wood and available from Amazon or some caving club libraries) which contains plots of the raw data from the experiments. Even to a non-geophysicist the results are very clear indeed. There are a couple of poor quality pictures in the Shepton Mallet Caving Club Journal Series 10 No.10 as well which may be easier to get hold of.
I do need to point out however that conditions were almost perfect, flat surface topography with large passages only a few metres down. Also the magnetic technique which proved the most use is probably completely useless in Limestone caves.
Hope this is of interest in the debate,
Ed
Ed W
Member
Andy,
I am no expert in this, but my impressionis that the lava has a magnetic field impressed due to the molten flowing rather than iron content. The magnetic technique apparently "sees" the boundary between the rock and the air (an M shaped response on the plots is typical for large passages as both sides of the passage are picked up).
The equipment in question was archaeological kit, and the operator thought that there may be a slim chance of picking up caves in limestone, on the grounds that the limestone would be different to the air of the cave passage, but that the demarkation would not be as clear as in lava. To my knowledge no-one has tried this out.
Cheers,
Ed
I am no expert in this, but my impressionis that the lava has a magnetic field impressed due to the molten flowing rather than iron content. The magnetic technique apparently "sees" the boundary between the rock and the air (an M shaped response on the plots is typical for large passages as both sides of the passage are picked up).
The equipment in question was archaeological kit, and the operator thought that there may be a slim chance of picking up caves in limestone, on the grounds that the limestone would be different to the air of the cave passage, but that the demarkation would not be as clear as in lava. To my knowledge no-one has tried this out.
Cheers,
Ed
langcliffe
Well-known member
Ed W said:
I think that you'll find that the lava has a magnetic field, as the ferric molecules were able to align themselves up with the eath's magnetic field when the rock was in a molten state. This is why one can date lava flows according to their magnetic orientation. If the technique described works, it may be because if there is a cavity, the magnetic field is detectably less strong.
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