Where do the Dwarves put all the stone from the Mines of Moria?

Question

In Lord of the Rings, the Fellowship of the Ring heads into the Mines of Moria to escape from the Watcher in the Water after attempting to cross over the Misty Mountains.

Inside the Mines of Moria there are skyscraper sized halls and there are dozens of them miles and miles long. There is even a deep shaft that, I'm assuming, they used for mining various precious resources

I know we should just stop thinking about the small details and accept it as movie logic but, realistically, where in the world would they put the millions of tonnes of stone that they would inevitably end up mining out?

We know from the books that Moria is taken back after the events of the movies (an epic detail I was pissed they left out in the movies). They would continue the mining and find riches galore.

My best estimate is that they pounded the stone into gravel and transported it up to build roads. Or cut the stone perfectly to use as building blocks for other cities and fortresses (like Minas Tirith, Helms Deep etc.).

By my estimates from a couple pictures I looked up and the movies, there aren't enough stone buildings/gravel roads to even come close to matching what they hollowed out in Moria (not including the lonely mountain kingdom). They would still have so much stone they wouldn't be able to do anything with it.

Answer 1

Moria is old.

According to The Silmarillion, it was founded by Durin I sometime after the elves awoke, during the Years of the Trees. This was a time before there was recorded time, before there was a sun and a moon, when all light in Middle-Earth came from two magical trees that grew in the far west, in the land of the Valar.

Tolkien was unclear as to how long time periods in the early ages of Middle-Earth were, not least because he kept changing the conversion factors. However, I found several estimates online that put the Years of the Trees at about 10,000 modern years. Durin awoke toward the end of this period, but this still gives him and his descendants a couple of thousand years to get starting mining the mountains.

We then have the First Age. Again, a modern time estimate is difficult because of the changes Tolkien made to his calendars but Wikipedia says it lasted between about 5,000 and 65,000 years.

Next there's the Second Age. We can be more specific at this point because the calendar used corresponds to the modern one, and it lasted about 3,500 years. The events of Lord of the Rings take place at the end of the Third Age which was around 3,000 years. It was during the Third Age that Moria was abandoned, about 1,200 years before the book begins.

So even the most recent rubble from the delvings of Moria has had 1,200 years to weather in the storms of the Misty Mountains. If you look at most monuments of that age that still stand in the world today, there's not a great deal left of them, even though they were built to stand and there have been strenuous efforts to preserve them. How quickly, by contrast is a slag heap going to be reduced to local pebbles and boulders?

To hammer the point home, that's the most recent excavations. Moria was a great city many thousands of years before that point and it seems a safe bet that most of the construction was done back in the glory days of the dwarves and elves. The remains of that have had anywhere between 10,000 and 70,000 years to weather away.

Answer 2

You're forgetting things like the "endless stair"; the dwarves didn't just mine down in Moria, they built hugely in the mountains surrounding those mines as well. The lake of the lurker at the western gates is almost certainly artificial, originally used to drive mechanised production equipment like bellows and trip hammers in the mine/city of Dwarrowdelf.

There's also some suggestion that dwarven masons who were employed far afield to erect fortifications sent home for dressed stone to build walls that would last the test of time.

When you think of the history of warfare and fortification in Middle-Earth, there are layers and layers of ancient cities and castles scattered everywhere. Some are just tumbled stones in farmers fields others are still semi-habitable like Weathertop, Dol Guldur, and Osgiliath, there has been a lot of stone cut for building work. If even a few percent of that came from the misty mountains they'd be completely hollow.

Remembering also that Moria is as old as the world, it was founded "by Durin 'the Deathless' in the far distant past, long before the creation of the Sun and Moon", it wouldn't take much export at all in any one year to add up to clearing out some huge spaces within the mountains.

Spoil from the mines would be produced so slowly (as a percentage of the material being mined because the dwarves are extremely skilled at cutting stone) that it could be dumped as fast as it was produced onto the mountains near the gates and build up talus cones that would be almost natural in appearance and vegetative processes, you'd never notice them in the landscape.

Answer 3

Geologist here. Answers by Matt Thrower and Ash are to the point: The material mined out of Moria had to go somewhere, and if the dwarves disposed of it in the usual way, there would be extensive cones of tailings flanking the mountains. Over the course of thousands of years, the tailings would develop soil and be covered with forest. They would not easily be recognizable to ordinary men or hobbits, though dwarves with their specialized knowledge would know them for what they were, and so would elves, because their long lives would make them aware of gradual change in the environment. Tailings piles from 500-year-old mines can be recognized in Germany.

By far, most of the material would not be slag, but gangue, the material that isn't wanted but accompanies the ore: ordinary rock for the most part. Halls in fresh rock could be quarried out as dressed stone, but no self-respecting dwarf would build a wall from most of the kinds of rocks that bear ores, as the seams are planes of weakness, and moreover are often made of sulfide materials that weather quickly in the open air. Dwarves would be well aware of the effects of long weathering after the first few centuries. So would J. R. R. Tolkien, if he gave the matter some thought.

Elves would probably not be very happy with the raw appearance of fresh tailings during Moria's heyday, but they would have been furious if dwarves polluted their waterways with sulfide mine wastes or cut down too many trees to roast sulfide ores, generating acid mine drainage and acid rain in the process. I think we can conclude that the ores were of a relatively benign composition and that dwarves were more careful than men with the environment.

Bottom line: The tailings are "hiding in plain sight."