Lightning Underground

D

Dep

Guest
AndyF said:
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.
Click to expand...

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!
 
M

mikem

Well-known member
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
 
Leclused

Leclused

Active member
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
 
G

grahams

Well-known member
Rummaging around at the back end of my memory, I remember reading that Norbert Casteret did a statistical survey regarding lightning strikes at or near cave entrances by looking for lightning damaged trees. I believe that he found a correlation and speculated that ionised air might be the conduit.

The British Caving Library has a reference to Casteret's book The Darkness Under the Earth.
 
M

mikem

Well-known member
This explains the theory (but no test of whether it's true), I'd expect the higher moisture levels of temperate cave air (compared to surrounding) to be a bigger factor:
https://www.irishtimes.com/news/the-effect-of-caves-1.20991%3f
 
Bob Mehew

Bob Mehew

Well-known member
Speleotron said:
Why is the air ionised around cave entrances?
Click to expand...
radon and its daughter products.  Work on measuring radon levels by BCA's Radon Working Group (see https://british-caving.org.uk/wp-content/uploads/2020/10/Environmental-Sampling-Results-for-BCA.xlsx) shows levels consistently higher than in the open air of between 5 and 10 Bq/m-3 (see https://www.who.int/news-room/fact-sheets/detail/radon-and-health).  So outward venting caves will have higher levels around the entrance than at some distance away.  Whether it is a meaningful difference in respect of a bolt of lightening arising in the cloud many hunderds if not thousands of metres above is another question.
 
S

Speleofish

Active member
I'd always assumed the issue was greater humidity, in the same way that lightning strikes on mountain crags tend to follow wet gullies and groove systems (where presumably radon isn't relevant).
 
M

mikem

Well-known member
The chance of getting struck by lightning generally is not that great (although some people have been hit multiple times), but is it safer to hide in an entrance?
 
pwhole

pwhole

Well-known member
Three of us went to Water Icicle Close Cavern about five weeks ago under threatening skies, and as I hit the base of the shaft, the most enormous clap of thunder erupted - it was amazing. My two companions got down rather quickly and told me there'd been a huge lightning flash directly overhead, and it's pretty exposed up there, with very tall trees about 20m away, so they didn't want to hang around to find out what happened next. It had all gone by the time we got out.
 
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