A Very Simple Explanation for How Lightning Killed 323 Reindeer at Once

You may have already heard the news that will surely terrify Rudolph-loving children for the next few months: 323 reindeer were killed by lightning in Norway this weekend. On Sunday, the country's Environment Agency released some pretty gnarly images and reported that the herd, which included 70 calves, was killed during some intense thunderstorms Friday.

Though the number of animals killed is unusual—I poked around and couldn't find solid evidence of this many animals being killed by lightning before—animals being killed by lightning isn't. Just a few months ago, 21 cows in South Dakota died when a lightning bolt hit the metal bale feeder where they were having a mid-rainstorm snack. It happens pretty frequently to cows, sheep, deer, and yes, reindeer.

But what exactly is happening when dozens, or hundreds, of animals are killed by lightning? Do multiple bolts strike in the same area, or does one bolt jump from animal to animal? Norway's environmental agents are investigating the incident, so they're still not 100 percent sure what happened, but looking at previous, similar mass animal lightning deaths gives us a likely answer.

Back in June of 1972, 53 caribou (which are also known as reindeer) were found dead in the Alaska tundra. A US Army helicopter crew doing training exercises spotted the downed herd and reported it to the state's department of fish and game, which investigated. They checked for signs of depredation, or poisoning, but quickly came to the conclusion that lightning might have been the culprit. For one, two caribou herds less than two miles away were completely fine. For another, there was a giant Lichtenberg figure—tree-like patterns created by high voltage electric charges—carved into the earth under the dead caribou bodies. Real good detective work, guys.

After investigating the pattern of the Lichtenberg figure, researchers were able to make an educated guess as to what happened, which they published in The Journal of Wildlife Diseases. At that time of year in Alaska, the frost has thawed, making the top layer of soil wet, but only a few inches down. Water, as you may recall from third grade science, has good conductivity. When the lightning bolt hit, it would have travelled horizontally along the top of the ground, spreading out to where the herd was standing as it snaked toward the nearest body of water: a nearby creek.

Unfortunately, quadrupedal animals like caribou are particularly susceptible to electrocution because their front and back legs are so far apart, allowing a greater potential difference to develop as the current travels from front to back (or vice versa). It's the same reason squirrels can chill on a power line without being electrocuted: there's no difference in voltage along the wire, so the current doesn't flow through the squirrel. But if Rocky touches a tree while still sitting on the wire, there's a difference in voltage (a tree has none, the wire has a lot), and the current flows through and fries him.

That's what the researchers suspect happened to the caribou: a single bolt of lightning hit the ground and the electric current spread horizontally along the moist top soil. As it hit the front legs of the caribou, a "potential difference developed between the animals' front and back hooves." That causes a jolt, which stopped their hearts, and that's how you kill 53 caribou in a split second.

And it's likely what happened in Norway this weekend. Just like the thawing Alaska tundra, the ground on Norway's Hardangervidda mountain plateau was soaked from the rainstorms. When lightning hit, it could travel horizontally along the top of the soil too, and the four-legged reindeer wouldn't have much hope of survival as the current hit them.

It's a bummer to see so many animals felled in one swoop, even if it was just Mother Nature being her brutal self. On the plus side, think about how psyched the scavenger species would have been to come across this giant, barbecued reindeer buffet. It was a good day for them.