The Physics of the Wall (Martin's, not Waters')

January 10, 2012 11:06 AM

Suppose there's a 700-foot-high wall of ice sitting in an environment that resembles, for the sake of argument, Alaska. I have some questions about the physics and long-term stability of such a structure.

Say this wall does include a foundation and some low-level backbone of very large stones, but it's mostly ice. While the air temperature is always below freezing, it's not uncommon for there to be sunny days where the wall "weeps" with meltoff. Moreover, there are men patrolling the top of the wall, and the friction of their presence is enough to require at least some reconstruction and reapplication of gravel for footing, etc.

My question is: would the wall be stable over a period of centuries, or even millenia? Or would the loss of mass from melting (and occasional Wildling attacks) eventually just whittle it down to a collection of frosty foundation stones? Would geologic activity result in cracks?

posted by COBRA! to grab bag (16 answers total)

I assumed that the small amounts that would melt off in the sun or chip off due to friction/attack would be replenished by water vapor in the air condensing to the wall and freezing. It could also be repaired easily when temperatures are very low by just pouring water on it, and I suspect that is part of the Watch's regular duties.

I never really questioned the stability of the Wall. I mean, it's just a sort of miniature man-made glacier, right?
posted by Rock Steady at 11:16 AM on January 10, 2012

While I'm not sure about just how stable the Wall truly would be, it is worth noting that the Night's Watch built up the wall every year for centuries. It is only recently that they haven't been adding the to height of the Wall.
posted by asnider at 11:19 AM on January 10, 2012 [2 favorites]

You're asking about Glacial Flow:

Ice behaves like an easily breaking solid until its thickness exceeds about 50 meters (160 ft). The pressure on ice deeper than that depth causes plastic flow.

posted by alms at 11:23 AM on January 10, 2012 [1 favorite]

The Wall almost definitely, in the real world, could not be built, let alone remain standing for centuries. Ice really isn't that strong. You're correct to be skeptical, I'd say.

Now for information specifically relating to GRRM's Wall...

As is hinted at by GRRM (arguably almost explicitly stated when you take what was said about Storm's End and apply it to the Wall, which was, according to legend, built by the same person), the Wall is held up by magic.

How that magic works, who knows. Like the rest of the magic in the series no one really has any idea what's going on. We know that it's some kind of persisting spell/whatever, because there are historical records of the Watch adding to the wall throughout the centuries.

For more, consult any of the several ASOIAF forums. I'd recommend A Forum of Ice and Fire
posted by Patbon at 11:23 AM on January 10, 2012

Sublimation would be one issue. It's why ice on the roads disappears without salt being placed on it, with below freezing temps all the while. Ötzi was kept hidden by new snow all the time. If you can't depend on new snow, sublimation will take place even if the area is shielded from the sun.
posted by jwells at 11:26 AM on January 10, 2012

It's pretty explicitly stated that there's magic involved in The Wall. Although it's usually described in terms of its protective nature, there's no reason to assume it doesn't extend to its structural integrity (which would be a prerequisite to the former.) There's also stone mixed in, although "currently" (in the books) it's mostly gravel at a maintainence level.
posted by ChurchHatesTucker at 11:32 AM on January 10, 2012

subquestion:
from context it appears you are all discussing some book/movie... can you share with the other kids?
posted by chasles at 11:56 AM on January 10, 2012 [2 favorites]

COBRA!: "in an environment that resembles, for the sake of argument, Alaska."

For the sake of argument, most of Alaska goes above freezing for months on end. Even Barrow (sort of) thaws in July and August.

"Air temperature always below freezing" is a much more difficult requirement than you might think it is.

Even Svalbard goes above freezing for a bit.
posted by schmod at 11:57 AM on January 10, 2012

aims totally has it. Ice under pressure, even when it is not melting, has a plasticity over time that causes it to flow. So, the Wall wouldn't even have to melt with high temperatures, it would simply ooze downward over time. However, if you actively added to the top and had some sort of way to contain it so it oozed directly downward, I suppose you could control it. People have been known to nurture glaciers, or create them. It happens in Pakistan. However however, I would think that the engineering structure that could control the sort of monumental force that a glacier commands would be crazy massive. After all, the only pointy peaks in Southeast Alaska are those that are so incredibly high that they avoided being totally smoothed out by a glacier flowing over them.
posted by Foam Pants at 11:58 AM on January 10, 2012

For the sake of argument, most of Alaska goes above freezing for months on end. Even Barrow (sort of) thaws in July and August.

"Air temperature always below freezing" is a much more difficult requirement than you might think it is.

Even Svalbard goes above freezing for a bit.
posted by schmod at 1:57 PM

fair enough; I was grasping pretty hard to find a real-world location that'd be a climate match, and guessed that northern Alaska would be the closest. But I'm definitely in talking-out-of-my-ass territory there.

Thanks for the thoughts, everybody; I hadn't really considered the fact that the Night's Watch would have been doing much more active maintenance in the past, which I guess would matter. And the glacial flow problem had never occurred to me.

I guess you have to sweep a lot of it under the rug as magic, but that's no fun.

subquestion:
from context it appears you are all discussing some book/movie... can you share with the other kids?
posted by chasles

It's from George R. R. Martin's Song of Ice and Fire books, starting with A Game of Thrones.
posted by COBRA! at 12:02 PM on January 10, 2012

(That said, if you're looking for a place that never thaws, Dome C, Vostok Station, or South Pole Station would all be candidates. Unfortunately, the area's geography, high altitude, and "never thaws" climate effectively prevent any walls of ice from forming)
posted by schmod at 12:02 PM on January 10, 2012

For chasles: A Game of Thrones is the first book in A Song of Ice and Fire, a series of epic fantasy novels by American author George R. R. Martin (wiki). In the novel, the author introduces a structure called The Wall that is so tall and massive that nothing can scale it. It separates the northern wild country from the more civilized south.
posted by Foam Pants at 12:03 PM on January 10, 2012

For information's sake, glaciers in Alaska don't really exist around Barrow. Those places are pretty flat and relatively dry. Alaska glaciers thrive in places with mountains climbing right out of the sea. The warm air from Southeast Asia comes up in a stream to the Southeast and South Central coast of Alaska where it meets tall peaks almost immediately. The sudden rise in altitude and the colder land mass makes the warm air dump it's moisture super fast. Then that snow sits at a high altitude where it doesn't melt completely each summer. Hence buildup over time.
posted by Foam Pants at 12:08 PM on January 10, 2012

I no reason ice couldn't function as the glue for a rock and ice wall of much more than 700 ft. without invoking magic.

In fact, we may be looking at a real-world example of many such walls-- and the disastrous consequences of the failure of that ice glue under the impact of Global Warming-- in the alps:

"Scientists now believe global warming is melting the Alps. The ice that for thousands of years had filled the deep cracks at the summit of the Dru has started to melt. The glue holding this rock tower together is leaking away.

More seriously, the crust of permafrost that binds the whole mountain range together is beginning to melt. The foundations of buildings, roads, mines, tunnels, cable-car stations and their supporting pylons are entirely dependent on the frozen solidity of this permafrost. As it steadily melts, the whole infrastructure of Alpine tourism is at risk, as well as a great many lives."

(http://www.independent.co.uk/environment/the-melting-mountains-514043.html)
posted by jamjam at 12:19 PM on January 10, 2012

Maybe the magic was pykrete?
posted by Yiggs at 3:29 PM on January 10, 2012

The surface of the wall is described as being solid ice and it is said somewhere that the Night's Watch added to the wall in the past by cutting huge blocks of ice from frozen lakes north of the wall and stacking them on top. There are also most definitely spells woven into the wall. At one point Sam, a member of the Night's Watch passes through a magic, talking door in one of the abandoned forts under the wall that will only open for members of the Watch and those with them.

There are also tunnels cut through the wall. If there is a core of pykrete and/or stone, it isn't discussed in the books. They do use some "rocks with ice as glue" to seal the tunnels of the abandoned forts (the one with the magic door notwithstanding) and the watch spreads gravel on the top of the wall to aid traction when they walk around up there. I think it reasonable that in the 8,000 years of its existence, a bunch of gravel has been integrated into the structure of the wall but it's mostly ice and magic.
posted by VTX at 8:27 AM on January 11, 2012 [1 favorite]