Alaska Pipeline Freezes the Ground It's Standing On. - Video

This is an oil pipeline that runs eight hundred miles across Alaska, and for four hundred and twenty of those miles it never touches the ground. It runs on stilts, in a zigzag, over the tundra.

Burying a pipe is cheaper, faster and safer in almost every place on earth. So why not here? Because of what the ground here is. It's permafrost. Soil that has been frozen solid for thousands of years. Frozen ground is hard. It holds weight like rock.

But the oil coming out of Prudhoe Bay is hot. It leaves the ground at up to a hundred and eighty degrees, and it goes into the pipe at around a hundred and twenty. Bury a pipe that hot in frozen ground and the ground stops being frozen. The ice in the soil melts, and what's left isn't dirt anymore. It's mud. The pipe sinks into it, bends, and eventually breaks. In the exact place where a break is hardest to reach.

So they lifted the pipeline into the air on seventy-eight thousand steel posts. Which sounds like it solves the problem, except it doesn't. Not by itself. Because those posts are driven into the same frozen ground, and steel carries heat straight down into it. So each post would slowly thaw the soil holding it up, and then the post sinks instead of the pipe.

Here's the fix. Look at the top of any post and you'll see two small pipes with metal fins on them. Those are heat pipes. There are more than a hundred and twenty-four thousand of them out there, and inside each one is ammonia. When the ground is warmer than the air, the ammonia boils, rises as gas, and gives up its heat through those fins. Then it condenses, runs back down as liquid, and does it again. No pump. No power. No moving parts. It only runs in one direction, pulling heat up and out.

So all winter long, every post is quietly refrigerating the ground it stands in, and freezing it deeper. That stored cold is what carries the ground through the summer.

And here's what it costs. The whole system assumes the winters stay cold enough to recharge that ice. As the permafrost warms, some of those posts have started to shift, and crews have had to install extra coolers to hold the ground in place.

The pipeline isn't standing on the ground. It's standing on ice that eighty thousand posts spend every winter making. That's why it stands.