Thunder and Lightning when out Walking and Hiking

Q. Hi - we're going up to the Peak District for the Bank Holiday weekend. I am concerned about being caught in a sudden thunderstorm in the middle of the moors.

What should one do to prevent being struck by lightning?

Many thanks.

Barbara Wardle, Greenford

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A. I agree with the Ed (see below) but would add that on an open Peak District Moor like Kinder, it might be quite a long way to a safe area.

For early warning - given a weather forecast of possible thundery showers, a small radio tuned in to white noise - with an ear-piece (don't want to disturb anybody) can give plenty of early warning about lurking thunder storms. The radio will emit sudden, sharp bursts of static interference and may give enough warning to get down the hillside - or even to the nearest lounge bar, where, I would suggest, the probability of being zapped is relatively slight.

If thunder and lightning is forecast - choose a walk with quick, easy escape routes.

Immediate danger is sometimes indicated by metal things sizzling or your hair standing on end - or odd or unusual weather - like the air becoming very hot and 'heavy'. One storm I encountered on Helvellyn was preceded by about fifteen minutes of the apparently dry ground suddenly emitting large quantities of mist.

Very immediate danger can be detected if a nearby sheep disappears in a blinding flash.

Mike Knipe, Crook

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The base of a thunder cloud is negatively charged.

On the ground beneath, positive charges are drawn into the 'footprint' area beneath the cloud - and the narrower the gap between ground and cloud, the more positive is the induced charge.

Once the electrical potential gradient reaches around a million volts per metre, the insulating properties of the intervening air break down and - ka-BLAAAAM! - lightning crosses the gap.

Since lightning can travel horizontally as well as vertically, strikes both precede the rain and trail behind it.

Charges can cluster more densely on convex objects than on flat or concave things - so the spikes on ice axes and walking poles are pretty good at building up a lightning-friendly charge; but the human head is marginally better.

Conductive channels are always welcome to a lightning bolt, so metal poles and axes may marginally increase the likelihood of a strike - but remember that this stuff has already blasted its way through hundreds of metres of air, so it's not going to fret greatly about the precise conductive properties of the last couple of metres to the ground.

Once you've been struck, it's even possible that a well-planted pole might save your life, offering a low-resistance pathway to earth that bypasses your heart - but that's probably not something you should rely on.

Don't rely, either, on your rubber-soled boots: Big Electricity, of the kind that comes looking for you across a kilometre-wide spark gap, will laugh at a couple of centimetres of rubber. This is stuff that, when it hits a car, simply blows out all four tyres on its way to the road.

When lightning hits the ground, current flows through the earth in a wide area around the point of impact. This is how a lightning strike can kill a field full of cows - the long wheelbase of the average cow means that a nearby strike induces a significant potential difference across the ground spanned by the cow's front and back legs; current flows through cow, cow dies.

From all this, it's easy enough to deduce some rules to maximise your survival chances if you're caught out:

Never continue upwards after warning signs (thunder, hair standing on end, humming metalwork).
Remove metal items, especially if they're pointy and sticking up off the back of your pack. Place them on the ground and move away from them.
Don't lie down flat - although it gets you as low as possible, it exposes you to a bigger ground voltage from a nearby strike. (Remember the cows.) Instead, crouch with your feet together and your head tucked down. Sitting on something relatively non-conductive (a rucksack, a coil of rope) is OK, but don't support yourself with your hands, as this spreads your area of ground contact. (Those cows again.)
Don't shelter under or near tall objects such as trees or cliff-faces - they're more likely to be struck by lightning, and you'll become incorporated into the current path. In particular, avoid cave-mouths and overhangs, which accumulate charge along their convex rims and may receive direct strikes.
If you're in a group, spread out and crouch separately - if one person is hit, the others will be uninjured and able to give immediate aid.
Don't be in a hurry to stand up again - let the storm pass over.
And if the worst happens: it's always safe and well worthwhile to attempt immediate CPR on a lightning casualty. Some victims suffer a period of paralysis and need no more than a bit of mouth-to-mouth to keep them alive until they can breathe for themselves again.

A. Personally I've never actually had to contend with a severe thunderstorm.

However, my understanding is that lightning strikes are more likely at the tops of mountains or other 'projections' from the ground. So if you find yourself on an exposed peak or ridge it's best to try and get down.

Once off the top, it seems that the risk is much less if you're out in the open and not sheltering in a cave or under a boulder.

To reduce the risk even further, try to find a broken scree slope and sit on top of a dry rucksack with your hands and feet off the ground.

Hope this helps.

Mike (Editor)

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