Thunder and lightning

Let’s delve into the topic of thunder and lightning, especially relevant for climbers and mountaineers during storms. Lightning dangers are a key consideration in these situations.

Storms are characteristic of the summer season, occurring from June to September, averaging 6-10 stormy days per month, typically in the afternoons and evenings. Anticipating a storm involves monitoring local weather conditions, such as cloud cover over the mountains, to gauge its potential direction.

However, the irregularity of cloud formations sometimes hinders precise predictions of the storm’s location. A more accurate assessment can be made by counting the seconds between witnessing a lightning flash and hearing the ensuing thunder.

An interval of 3 seconds between lightning and thunder means the storm is about 1,000 meters away. On a plain, thunder can be heard up to 20 km away whereas in mountainous areas the sound is stopped from carrying by the high peaks. Echoes can however confuse the violence of the storm.

Without going into the details of storm electricity, we can say here that it is friction electricity, or electricity generated by the friction of water droplets in contact with ice particles in the clouds, agitated by winds.

The electrical discharges can be observed even before the rain starts to fall. The lightning hazard decreases when the sky is covered evenly by grey, rain-laden clouds.


Lightning dangers in the mountains

The generation of electrical energy and its release occur as a result of the interaction between positively and negatively charged areas within storm clouds, or between charged portions of the storm and the ground. Lightning bolts can reach up to 20 km in length. The electrical discharges taking place between clouds are rather hazardous for outdoor people, especially if we are up on a mountain that is fully covered by clouds. The worse hazard comes when lightning strikes the ground and although the strikes can having various ramifications, this type of lightning almost always involves a main branch striking the mountain peaks. Also, lightning often returns to strike in the same zone.

It is very important to be aware of the lightning hazard and, when it becomes impossible to avoid the storm, to know how to shelter from it. Experience teaches us that the hazard is greater on rock than on snow or ice. This applies particularly to the so called Fuochi di S. Elmo (“St. Elmo fires”), which is a silent form of lightning produced in air that is electrically highly-charged.

The “fires” occur as bluish flames that arise from pointed metal objects, such as the crosses on mountain summits, electricity pylons etc.. Sometimes you can also hear crackling.

In the presence of lightning dangers, it is crucial to distance yourself from upward-pointing rocks and anything that could serve as a potential strike point. Stay well away from cables, electricity pylons, trees, or isolated rocks. Avoid water and drain pipes, and vertical walls, and, as much as possible, keep away from metal objects.

Even seeking shelter under a rock is not advisable, as electricity can travel down through the rock, posing a continued danger. In summary, while it may sound obvious, we strongly recommend finding shelter before the storm reaches you. The choice of shelter and its location depends on exercising good judgment.

Lightning dangers.

The most serious hazard of storms is lightning, which is a discharge of electricity either among clouds, or between clouds and the ground. Lightning has a temperature of 30,000 Celsius and its speed is 10,000 km/sec. You can find more information about thunder and lightning here.


The danger of impending lightning is heralded in these ways:

  • Exposed areas of the body experience a tingling sensation.
  • Goosebumps on the skin and hair standing on end.
  • Buzzing and faint sounds emanating from metal objects.
  • Bluish flames (“Fuochi di Sant’Elmo”) around particularly exposed metal objects (e.g., poles, pylons, mountain summit crosses).

What to do in the event of danger?

  • Avoid crests, spires, and peaks; maintain a safe distance from them (at least 15 meters).
  • Keep a distance between yourself and the metal components of your equipment, such as climbers’ crampons, picks, carabiners, bolts, “friends,” etc.
  • Steer clear of gullies, crevices, cracks, chimneys, and other shelters like cavities, caves, large isolated rocks, and trees.
  • Avoid equipped climbers’ routes with cables and metal rung-ladders (“via ferrata”) or exit them promptly.
  • Move away from sheer rock faces and sit with feet together, knees bent up, and held against the body (see fig.1).
  • Always double-check belays and secure your descending device with a backup like a Prusik, Machard, or similar when abseiling.
  • Snow expanses and glaciers are potentially safer than rocky areas.
  • Avoid herds of animals or groups of people.