Au Tour du Mont-Blanc Project

Storms

How to protect yourself from storms

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Storms are commonplace in the mountains, especially on hot summer days. Some kinds of storms can develop very rapidly even when the skies are clear.

When this kind of phenomenon is approaching, move away from peaks, ridges and waterways, do not take shelter near runoff channels or chimneys and distance yourself from solitary trees and standing structures (pylons, poles, unusually tall solitary masses...).  Move downhill and seek out dry cover.

If you are in a group when a storm takes you by surprise, leave about 10 meters between each individual (not hand in hand) as you search for shelter. Insulate yourself from the ground using your backpack, rope or any other poor conductor and get rid of any metal objects; do not light fires (which can attract electrical discharges) and wait out the storm: the average duration is about an hour.

To reduce the risk of being struck by lightning, the following should be added to the above precautions:

  • if you have not already done so from home, check the conditions and weather forecast for your route at the guide offices;
  • if you notice vertically developed clouds in the morning, then storms are likely to develop during the course of the day, and are even more likely if there is haziness and a sensation of stuffiness in the valleys;
  • for storms that are already under way, the highest part of the cumulonimbus cloud (typical anvil-shaped cloud) will point out the direction in which the storm is headed;
  • at nighttime, lighting flashes will be visible tens of kilometers away, but if you can hear the thunder then the storm is only a few kilometers away; a delay of about 10 seconds between the flash and the thunder means that your are about 3 kilometers away from the storm (no. of seconds x 340 m);
  • remember - the average storm lasts about 1 hour, and the most intense phase rarely lasts longer than a half hour, so look for shelter (inside caves, not at the entrance) at the first signs of a storm and wait there until it begins to wane;
  • stay away from rivers, which can rise rapidly and present a threat;
  • direct lightning strikes are hazardous, but so are the so-called "ground strikes": the current from the lightning passes through the ground, decreasing in intensity as a function of distance from the strike point - as a consequence, it is important to be touching the ground surface at one point only, e.g., by standing on one foot or crouching with your feet together (there can be a dangerous difference of potential between the sole of one foot and the other; avoid lying down or leaning against the rock;
  • even minor lightning strikes can generate enough current to trigger respiratory or cardiac arrest, burns and involuntary muscle contractions that can induce jerky, uncontrolled movements and even bone fractures. Powerful lightning strikes usually result in death.

After being struck by lightning, however, the victim is not electrically charged and it is safe to administer first aid. The survival rate for lightning strikes is about 80%: save a life with mouth-to-mouth respiration and cardiac massage (CPR)!