On Jan 5, 10:08*am, Jim wrote:
mgg wrote:
"Frogwatch" wrote in message
...
On Jan 4, 10:27 pm, "mgg" wrote:
"Frogwatch" wrote in message

....
On Jan 4, 8:00 pm, Wayne.B wrote:

On Mon, 4 Jan 2010 14:39:09 -0800 (PST), Frogwatch
wrote:
I resolve to carry a compass even on
short trips into the woods from now on.
A pocket GPS is even better, and useful in the dinghy also.
In deep woods, GPS often has problems and does not work at all in
caves.

I have to wonder how well a compass would work in some caves as well.
Depending on the composition of the rock, it could drive a compass whacky.

Here's a thought... carry both! ;-)

--Mike

My compass has never failed me. *Most *caves are in limestone so
compositioin does not change the earths mag field.

Limestone.... I did not know that.

My only experience with caves is: *http://www.mercercaverns.com/which is
limestone as well. I didn't know it was the norm though. Very cool tour
there as well. I doubt it's your cup-o-tea since they built steps. ;-)

--Mike

We toured Lurray Caverns up in Hairball the paste eater's neighborhood,
this summer. Pretty Cool place. They even had a mechanical organ that
used ( limestone icicles ) stalactites, i think, instead of pipes. It's
worth a look if you are traveling in the vicinity.

You would think that in 2010, there would be Hi Tech ways to navigate
in caves but there are not. Neither GPS nor LORAN nor any radio
communications work in most caves due to the large amount of water in
the overlying rock. it is like communicating with a submerged
submarine but even worse because SONAR does not work well through
discontinuous rock either.
Consequently, mapping is still done the old hard way, with compass,
clinometer and tape measure. There are also no good ways to find
caves. Ground Penetrating Radar rarely works in such an environment
because of insufficient range and because the ground is always too
uneven. So, the best ways to find caves is to be very familiar with
terrain. One gets a subconcious sense of terrain noting odd ridges
and areas where water flows in but not out. Being obsessed with Topo
maps is also good. Still, one has to go look for them not knowing if
they exist which means walking for miles through "cavish" terrain. I
have noticed around here certain types of vegetation that grows near
caves such as "Oak Leaf Hydrangea". One friend of mine says he can
smell caves and his record of finding them is good.
Cave maps are normally difficult to use because they are two
dimensional whereas caves are three dimensional. Often maps give side
views but not often enough. The maps are also drawn mostly based on
simple sketches made by the mapper under really bad conditions so
interpretation is difficult. Maps can be used to tell where the cave
passage is under the surface but you have to realize the extent of the
errors due to the difficult conditions. Try reading a compass while
your face is buried in the mud and the compass itself is covered with
mud and you have to let the air out of your lungs to squeeze through
and you might see why there are errors.
Communication underground is basically impossible. Radio does not
work and neither do cell phones. A device called "Cave Radio" does
exist using extremely low frequency but it cannot be used for much
because it's data rate is very low and it requires a very large
underground antenna. Its spatial resolution is also very poor.
Consequently, once underground, you are on your own with no way to
communicate with the outside world. You might be only 100' below
ground but you might as well be on the back side of the moon.
Even if you do have GPS coords of a cave entrance, finding it can
still be very difficult. First, you have to get there which is often
bizarro difficult. Many entrances are REALLY SMALL and non-obvious.
The GPS might say you are within 60' of it and you cannot find it.
Once you find it, you have to consider what is living in the
entrance. Around here it will be snakes or buzzards. Buzzards
protect their nests by barfing on you, I know, experience, truly
disgusting.
In spite of all of this, it is probably the most adventure you can
have for the least amount of money.