Measuring Deep Pits

[Ralph E. Powers]

Just a note - much better than cotton thread it is the linen thread because it is not so elastic. I bought several boxes of old surgery linen threads many years ago and I used them. I use Disto now, but for deep pits topofil was the best tool. One was able to measure depth of unexplored pit too. And if the thread was connected to small balloon with helium it was possible to measure the height of chimneys too.

Martin

Interesting... how did you manage to not pop the balloon enroute to the chimneys? Or did you use a mylar type which are tougher? Also thinking that the higher a balloon goes on a tether the heavier the weight of the line attached to the balloon gets thus a balloon could conceivably stop climbing because of the weight. I imagine fishing line would be a good tether as it's relatively light-weight.
I know of a few high domes that could use the same type of measuring. Be interesting to see just how high up they are. Unfortunately they're all in Utah and I'm here in TAG. Ah well... a reason for a road trip.

[Martin Sluka]

how did you manage to not pop the balloon enroute to the chimneys?

It is long time ago. No mylar balloons that time. Standard latex children type. Only problem was the helium diffuses through latex quite fast, so we had to measure quickly. But the very small cylinder (0.25 l) with helium was enough for a surveying trip. 1 l of helium is able to take more than one gram.

[George Dasher]

Wrong book--not On Rope, but On Station.

From page 59...

"The depth of Greece's Abyss of Provatina was measured by hanging a short rope into the pit, then having someone descend the short rope and measure the main rope in sections as it was pulled out of the cave and still under tension."

The original article was by Fred Wefer, "The Abyss of Provatina, A Schematic Perspective," Compass and Tape, Winter 1988-1989.

I don't know how deep "the Abyss" is, but it is more than 1000 feet.

[Stelios Zacharias]

"The depth of Greece's Abyss of Provatina was measured...

I don't know how deep "the Abyss" is, but it is more than 1000 feet.

Provatina is currently considered to be -405m deep. It was first bottomed in 1968 and consists essentially of just the one big entrance shaft. There have been technical climbs to windows in the shaft (by SELAS Caving club) in the late 1990s which have yielded small chambers but no more depth. Once one of the deepest caves in Greece, at the moment Provatina is now in position 12.

[Cheryl Jones]

We had good success using thin bare copper wire, as is used for winding small eclectic motors, for measuring deep pits. The important advantage of the wire over nylon fishing line or cotton thread is that it has negligible stretch. Additionally, it is strong and flexible. Sorry I can't remember the gauge. But imagine something a little thicker than normal thread but a thinner than heavier-duty button thread. An electronics buff out there might have the answer.

We'd wind the wire on a fishing line spool (with an angled rod bolted through the center to help it roll to wind it back on) and hook a fishing weight to the end of the line. Seems like the weight was 4-6 oz. Just enough to weight the wire and keep it straight. We'd spool out the wire down the pit, and letting it run over a finger so it was easy to feel when the weight hit bottom (or a ledge.) Sometimes if the drop was not clear or free, it was helpful to have someone at the bottom to ensure that the weight made it to the floor. (But don't run the wire down next to a rope, or it will wrap around it for sure! Most likely when it is being wound up, for the weight can get to swinging.)

To fix a measurement, we would lightly tie a small figure 8 loop in the wire right at the lip of the drop, with the weight just on the bottom. Then roll up the wire back onto the spool. Several pits could be measured on one trip, simply by tying more knots. (and marking the loops with string, or whatever, to match the knot to the pit later if needed.)

On the surface, we'd roll out the wire along a parking lot or sidewalk, then with it and a tape pulled taut, we'd measure the wire. Usually the pit was deeper than our tape so several careful measurements along the wire had to be made. Tedious, but far more accurate than using a line with inherent stretch.

Untie the knot/s, and the wire is ready for the next pit.

I haven't used the system in several years, so would need to see if it is in my trunk of all things caving and check the weight and perhaps discover the gauge of the wire....if anyone's interested.

Cheryl

[ian mckenzie]

You can also stick a light on the bottom of the line, when it stops swinging about you've touched bottom.

[ian mckenzie]

Only problem was the helium diffuses through latex quite fast, so we had to measure quickly. But the very small cylinder (0.25 l) with helium was enough for a surveying trip. 1 l of helium is able to take more than one gram.

In 1968 cavers here used a balloon to measure an aven in Castleguard Cave. They mixed zinc and hydrochloric acid on site to inflate the balloon with hydrogen and achieved a measurement of 62.8 metres. Back then they would have been using open-flame carbide lamps so I'm sure they were careful... The aven was also measured when it was finally climbed in 2005 by the rope-length method, at 68m.

[Bob Thrun]

We had good success using thin bare copper wire, as is used for winding small eclectic motors, for measuring deep pits. The important advantage of the wire over nylon fishing line or cotton thread is that it has negligible stretch. Additionally, it is strong and flexible.

Iron or steel wire is cheaper, stronger, and has less stretch than copper. The only advantage to copper might be ready availability in continuous lengths.

[Ralph E. Powers]

We had good success using thin bare copper wire, as is used for winding small eclectic motors, for measuring deep pits. The important advantage of the wire over nylon fishing line or cotton thread is that it has negligible stretch. Additionally, it is strong and flexible.

Iron or steel wire is cheaper, stronger, and has less stretch than copper. The only advantage to copper might be ready availability in continuous lengths.

I can probably see how steel or iron would be stronger and cheaper... but problem is that it in a coiled state would have to be kept well away from the compass instrument to prevent any magnetic interference with the azimuth reading. So one could keep the coil in their pack and at least 5-10 feet away from the compass, do a reading then measure out the pit. But then I'm not sure the effect on the accuracy of the compass should the two be kept together in a pack, unless one caver carries the coil in their pack and the other carry the instruments in theirs.

[Jeff Bartlett]

how much does copper wire actually stretch?

[Bob Thrun]

I can probably see how steel or iron would be stronger and cheaper... but problem is that it in a coiled state would have to be kept well away from the compass instrument to prevent any magnetic interference with the azimuth reading.

The 510 ft drop in Ellison and the 437 ft drop in Fern are complety free. There is no magnetic reading

[fuzzy-hair-man]

Only problem was the helium diffuses through latex quite fast, so we had to measure quickly. But the very small cylinder (0.25 l) with helium was enough for a surveying trip. 1 l of helium is able to take more than one gram.

In 1968 cavers here used a balloon to measure an aven in Castleguard Cave. They mixed zinc and hydrochloric acid on site to inflate the balloon with hydrogen and achieved a measurement of 62.8 metres. Back then they would have been using open-flame carbide lamps so I'm sure they were careful... The aven was also measured when it was finally climbed in 2005 by the rope-length method, at 68m.

I was on a trip as a sherpa around here to photograph the top of Gunbarrel aven around here and it's ~90 -100m, so there was a remote controlled camera suspended from the bottom of 3 helium balloons made with dry cleaner's bags, unfortunately there was fog at the top of the aven despite our best efforts to avoid it (changing into dry clothes) so the camera couldn't see a lot higher up. also the remote control lost control as it got higher up. Still it was great fun to be along.

There's a couple of photos and a bit about it here:
http://www.canberraspeleos.org.au/projects.html

[lleblanc]

If you have an Auriga-enabled palm, there is a "pit sounder" feature that does the math for you. But you're right, NOT accurate enough for a survey.
How well would you be able to hear a rock hit bottom on a 2000' pit anyway? You'd have to roll your truck in there!

While it may not be survey grade, a test we did in a 116-m open air pit in Spain gave 114, 115 and 117m! There's a picture of that trial in the news column of the Auriga website. The math involved is way more complex than applying a simple mnemonic formula, but involves an iterative time-slicing process that takes into account the air resistance (on a spherical rock), the density of limestone and the speed of sound in moisture-saturated air.


Luc Le Blanc
http://www.speleo.qc.ca/Auriga