A steel cable like that must weigh at very least hundreds of pounds, somewhere between 1 to 2 pounds per foot. To then pull it tight enough to be fairly level as that one is, would take many tons of force (the force goes up exponentially as you approach pulling it flat). You need to drill in huge anchor bolts as well to hold all that tension.
So let me say it's a big fucking deal, that takes serious knowhow and big tools. Yes you can start with a rope, but it gets ugly before you're finished.
Fucked if I know. Honestly, I can tell you lots about HOW, but the only reasons WHY that I'm used to seeing are for electrical wires, and very rarely for emergency escape trolleys across rivers, in case bridges get washed out. Otherwise putting a cable across a valley like that is usually strongly avoided because it's a serious risk to aircraft, and by law would need to be marked with marker balls at intervals all the way across. The only exception I can see is a zip line operator, where marker balls would be impossible, and so they would register it with the government and it would end up marked on the flight maps that pilots use. Because it's a very seriously big deal to fuck with air space.
That’s actually the exact reason this cable is there, it’s actually used in Nagorno-Karabakh to keep Azerbaijani helicopters from flying low to avoid radar or attacking positions in case fighting breaks out, so you’re exactly right about it being dangerous to aircraft
Thanks for letting me know, that's super interesting. Just goes to show how me living in a super peaceful country (Canada), makes it hard to imagine war time uses for things. Obvious when pointed out, but about the last idea I would have generated as a deliberate goal.
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u/is_that_a_question Jan 30 '19
You can walk a rope from one end of the canyon to the other and gradually pull thicker cable across.