I have a friend who is a high-energy electrical engineer and a whitewater open boater (canoe) that I often run rivers with. I remember one trip when we were on the Fife Brook section of the Deerfield River in Western Massachusetts and a big thunderstorm boiled up. We got off the river and hunkered down on the shore on top of an old stone bridge piling. As we waited for the storm to pass, he told me some stuff about lightning safety, particularly ground current, that I did not know and that is worth passing along in a backpacking context.
There are three different ways that of lightning can harm you: direct cloud-to-ground strikes, side flashes, and ground currents. In a cloud-to-ground strike, two arcs of energy meet, an upward leader, emanating from a high point such as a tree or mountain top and one emanating from a cloud. These complete a circuit and create the flash of a direct strike. Direct strikes like this are relatively rare but can cause serious burns and stop the heart.
Side flashes occur when the cloud-to-ground strike fails to meet the upward leader and is attracted to another high point which is more conductive. Side flashes can arc through the air or travel over the ground and carry the same energy as a direct strike. Injuries due to side flashes are much more common than direct strikes.
Ground currents occur once the lightning has hit the ground. From there, it emanates from the point of the strike, dissipating along pathways such as wet rocks, crevasses, and tree root systems. Injuries from this type of lightning strike are also quite common and are just as serious as side flashes and direct cloud-to-ground strikes.
To minimize your risk from lightning, you want to get away from tall trees and away from mountain peaks or high ridges. If you are near or on the water, you want to get to shore and avoid wet areas that can conduct ground current. And if you are in a field, you want to get out of the open to avoid being the high point.
You can further protect yourself by squatting on top of your pack or a sleeping pad or on a boulder that sits on top of other boulders. If you can squat without your hands touching the ground, ground current will travel up one leg and down the other rather than traveling up your torso and cooking your major organ groups.
That day on the Deerfield, we were primarily concerned about ground current because we were wet and rain had begun to fall making the ground more conductive. In response, we climbed up on some dry rocks sitting on top of an old stone bridge piling and waited out the storm sheltered under some old bridge decking.
I never knew about ground current before that day but I can completely understand how it could be a big concern for backpackers. Since it is unlikely that you will be able to shelter under an old bridge like we did, it helps to be understand the simple actions you can take to reduce your risk.
Photo Credit: KcdsTM, Some rights reserved.
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