Author Topic: Lightning Underground  (Read 4362 times)

Offline Peter Burgess

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Lightning Underground
« on: December 29, 2006, 10:47:01 am »
This is something I hope I never witness. Has anyone got any experiences of this dangerous phenomenon? I believe it is more common in mountainous areas - lightning being drawn to cave entrances, and then passing down shafts. Mine-shafts also are supposed to be prone due to the steelwork and gear conducting the charge down underground.

Offline Les W

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Re: Lightning Underground
« Reply #1 on: December 29, 2006, 10:47:37 am »
J Rat and Blitz have  :o
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Offline Peter Burgess

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Re: Lightning Underground
« Reply #2 on: December 29, 2006, 10:56:27 am »

Offline Peter Burgess

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Re: Lightning Underground
« Reply #3 on: December 29, 2006, 11:01:36 am »
And has anyone seen what, if any, effect lightning has on a cave? Any signs of damage or change to the cave walls?

Offline Les W

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Re: Lightning Underground
« Reply #4 on: December 29, 2006, 11:05:03 am »
I'm a very busy person

Offline ditzy

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Re: Lightning Underground
« Reply #5 on: December 29, 2006, 11:06:17 am »
i havent and i hope i dont ever witness it

Offline AndyF

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Re: Lightning Underground
« Reply #6 on: December 29, 2006, 11:10:50 am »
I can understand lightning striking near a cave entrance, due to (for instance) damp air coming out, but I don't beleive it is possible for lighning to travel down  a shaft. The reason is that ground (all ground) surrounding a cave or anywhere else is (by definition) at ground potential. The lighning would, therefore, have to be passing points of ground potential to travel down a shaft, yet the shaft cannot be below ground potential.

Electrical sparks always take the line of least resistance, and therefore could not "pass" a zero point at ground level.

This is rather like a Faraday Cage effect, and is the same reason why people don't get electrocuted or fryed when lightning strikes an aircraft, the lightning is unable to penetrate INTO the cabin as it ca't pass the surface skin.

Mine shafts with metalwork (such as a headgear) ABOVE ground are different, as a 100 foot high headgear will bring a higher potential point (from 100 feet up) all the way down to the bottom of the shaft (if there is metal work to conduct it) causing a local variation in ground potential. A strike on a headgear would certainly cause spitz 'n sparks at the bottom of the shaft.
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Offline Peter Burgess

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Re: Lightning Underground
« Reply #7 on: December 29, 2006, 11:14:15 am »
Could the charge not pass onto the walls of a shaft as it dissipated into the ground? When lightning strikes the ground, does the charge not penetrate into to soil and rock for a short way? If the ground is in effect the walls of an open shaft, where does the surface end, and underground start?

Offline Les W

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Re: Lightning Underground
« Reply #8 on: December 29, 2006, 11:20:45 am »
I believe lightning is atracted to cave entrances as the air is ionised. J Rat was in the entrance to a cave in the Dachstein and Blitz was underground, a contributary factor was that they were on the telephone to each other at the time. The lightning travelled along the phone wire.  :o

Whilst the ground is at "ground" potential, lightning can still "elevate" the potential in an area, this is why livestock dies when there is a lightning strike nearby, the current flows up their front legs, through their heart and back down their back legs (or vice versa).
Bipeds (humans) don't suffer from lightning strikes as badly because we don't offer a route of lower resistance to the current path as
a) our body resistance is acyually quite high compared to other animals and
b) the current path is non existent as our feet are quite close together so the route through the earth is prefered.

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Offline Peter Burgess

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Re: Lightning Underground
« Reply #9 on: December 29, 2006, 11:26:14 am »
http://www.mininginstitute.org.uk/papers/lightening.html

Try this for a graphic description of a strike on a coal pit.

Offline Peter Burgess

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Re: Lightning Underground
« Reply #10 on: December 29, 2006, 11:31:05 am »
Quote
a contributary factor was that they were on the telephone to each other at the time. The lightning travelled along the phone wire.


I was going to suggest that perhaps a wet rope might offer a path of low resistance, but a phone wire is more likely. Thank God for Heyphones!

Offline AndyF

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Re: Lightning Underground
« Reply #11 on: December 29, 2006, 11:33:07 am »
Yes, there is a local bounce where the lighning strikes, and it may be possible for it to get a meter or so down the shaft.

The key thing with the "Blitz" example is the telephone line, that draws on the mine shaft analogy. Caves usually won't have such a conductor, but may possibly have a wet rope (!)

The cattle dying is more complex, as they are above ground. During a lighning strike, the local potential may be a few hundred volts per inch above ground, so a cow being say 5 feet high may have a potential difference of several thousand volts from toe to tail and it is this IMO that would cause the death. Doubt that a cow lying down would die. This is why people are told to lie down if caught in the open.

I seem to recal this being documented on the Gahr Paru expeditions, where severl strikes were experienced at the entrance.
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Offline Elaine

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Re: Lightning Underground
« Reply #12 on: December 29, 2006, 11:39:41 am »
We don't hang around long at Templeton if there is a thunderstorm! For those who don't know what Templeton looks like, the railtrack makes a good conductor to the bottom with 6 metal platforms and umpteen other bits of metal. At the top of the rail track is a pole with a light fixed to it saying "look lightning, here I am!"
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Offline Peter Burgess

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Re: Lightning Underground
« Reply #13 on: December 29, 2006, 11:53:38 am »
What if the shaft or cave is draughting out? Might the air be charged in a way that it might attract a strike? Especially if the cave contains falling water. I seem to recall an experiment at school using falling drops or a spray of water to build up a charge on a metal plate.

Offline Brains

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Re: Lightning Underground
« Reply #14 on: December 29, 2006, 11:56:09 am »
I have heard of cavers being struck in a shallow system where the strike hit the ground above, and then arced across the passage below. I believe it was in the 'states but I cant recall the details. May have been more of a static discharge than a full on bolt. A friend of mine was zapped on the 'Midi by this when a bolt hit the other side of the telephrique station, causing a discharge off the handrail. Painful for them, funny for us...

Offline gus horsley

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Re: Lightning Underground
« Reply #15 on: December 29, 2006, 12:30:55 pm »
There's been several recorded incidences of the Gaping Gill "Ghost" which is presumed to be an electrical discharge from the winch guide line.

Offline Pitlamp

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Re: Lightning Underground
« Reply #16 on: December 29, 2006, 02:09:02 pm »
There are quite a few tales about the problem from 20+ years ago, when many folk were still using electron ladders down pothole entrances.  I remember the Bradford having a near do down a deep cave in Italy around that time.  I guess it's not quite so bad now that electron ladders are used less frequently - except of course in tight entrances or especially digs.  I've never heard much about this problem when a pothole was rigged on rope.

Offline Peter Burgess

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Re: Lightning Underground
« Reply #17 on: May 10, 2007, 11:42:46 am »

Offline menacer

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Re: Lightning Underground
« Reply #18 on: May 10, 2007, 02:42:04 pm »
We don't hang around long at Templeton if there is a thunderstorm!

Dont blame you.  :o
However should you find yourself trapped in there with lightening on the surface ...hop out ...using only your right leg and right arm to climb the ladders...that way the path of electricity as quoted by Les will not pass through your heart....the human beings main Stop valve....
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Offline Mrs Trellis

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Re: Lightning Underground
« Reply #19 on: May 10, 2007, 03:05:26 pm »
Jimmy Lovelock was climbing an electron in the Berger entrance pitch when it was struck by lightning and he was thrown off it.
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Re: Lightning Underground
« Reply #20 on: May 10, 2007, 04:01:43 pm »
Yes, there is a local bounce where the lighning strikes, and it may be possible for it to get a meter or so down the shaft.

The key thing with the "Blitz" example is the telephone line, that draws on the mine shaft analogy. Caves usually won't have such a conductor, but may possibly have a wet rope (!)

The cattle dying is more complex, as they are above ground. During a lighning strike, the local potential may be a few hundred volts per inch above ground, so a cow being say 5 feet high may have a potential difference of several thousand volts from toe to tail and it is this IMO that would cause the death. Doubt that a cow lying down would die. This is why people are told to lie down if caught in the open.

I seem to recal this being documented on the Gahr Paru expeditions, where severl strikes were experienced at the entrance.

The potential difference across the length of a body idea is correct.
But it is a 3 dimensional field so also applies radially from the strike point.

So simply lying down does not reduce the risk; worst case is that you feet are twordas the strike and your head away, and then you have a potential difference along the steepest gradient of the electric field - along the 6ft or so of your body.

That's why the instructions suggest that if out in the open you should also curl into a ball with your lower back/arse as your highest point - shortest path is arse to knees!

Online mikem

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Re: Lightning Underground
« Reply #21 on: August 31, 2021, 08:40:33 am »
Thought I'd resurrect this thread as something similar came up on Bad Caving Tips FB page & I found this discussion from across the pond:
http://forums.caves.org/viewtopic.php?f=13&t=3691

Offline Speleotron

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Re: Lightning Underground
« Reply #22 on: August 31, 2021, 03:55:56 pm »
Why is the air ionised around cave entrances?
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Offline Leclused

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Re: Lightning Underground
« Reply #23 on: August 31, 2021, 05:38:23 pm »
During one of the first Anialarra expeditions (psm France) lighthing struck an entrance and travelled down the wet rope. One of the members was on that rope and the current travelled through him without causing any harm.

So yes it can happen
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Online mikem

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Re: Lightning Underground
« Reply #24 on: August 31, 2021, 10:49:57 pm »
It will do, provided your body doesn't act as a short to another surface....

 

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