How can I justify that dunes keep drifting and cannot be stabilised?

Question

I have the idea of a fantasy civilization based around shifting dunes. The idea is that the land is largely uninhabitable except for the coasts, but there are large dunes that function as habitable "islands" in this wasteland. Blown by the wind, these dunes slowly drift across the land at the speed of several metres per year, like the somewhat famous Råbjerg Mile in Denmark.

Maybe the soil on this continent is toxic due to pollution by a past civilization so that little can grow there, whereas the dunes carry with them not only sand but also fresh, healthy soil (maybe loess) - and there's plenty of rain, so lots of plants can grow on the dunes.

These dune-dwellers are somewhere between settled folk and nomads, since it can take years for a dune to move a distance equivalent to its own length.

There is a problem, however: Råbjerg Mile only keeps moving because of conservation. You can arrest dune drift by building fences and planting the right plants.

If my dune dwellers can just stabilise the dunes, that's no fun. Then they'll soon be just like any other settled folk. This is only fun if there is a good reason why they cannot lock down the dunes.

Having a superstitious taboo against stopping the dunes is not good enough. It's not satisfying for me to have a culture built on stupidity. That also sounds unstable. I need a better reason than that.

It's important to note that this is fantasy, not science fiction. Supernatural explanations are acceptable.

Thanks in advance!

Answer 1

Small dunes can be stabilized. Large dunes do what they want without caring of what those little furless ants say.

I remember my Earth science book in high school with two photos of the same dune taken few years apart: a road that once went straight in front of the dune had been swallowed by it and had to curve around the dune front.

If fencing would have been effective at protecting that road, why would have they moved the road?

Answer 2

The ground isn't uninhabitable, it has hostile inhabitants.

The ground has hostile mutated animal swarms that attack anything loud. You can avoid them, but you can't avoid them if you are building walls to hold in your wind blown homes, as the animals come in, knock down your walls, and kill your workers.

There's a cultural taboo against blocking the movement for good reason.

The movement helps refresh the resources of the dunes and regenerate them. Cultures that do manage to kill enough worms and overcome the challenges to anchor their dunes in place tend to die out, as they run out of resources. Then their walls collapse in time, and the dune moves on. These graveyards are a great place to explore and colonize for bold explorers.

Answer 3

I suspect you need the right kind of plants, not just any plants. Wikipedia has an article on sand dune stabilisation which seems to confirm this:

Overview (as you stated) - Planting vegetation reduces the impact of wind and water. Wooden sand fences can help retain sand and other material needed for a healthy sand dune ecosystem. Footpaths protect dunes from damage from foot traffic.

Detail summarised: The location of the dune limits the types of plant that can thrive there...... Plants that thrive on the foredune must be tolerant to salt spray, strong winds, and burial by blowing/accumulating sand.... Plants which thrive on the broad dune plain and backdune grow together into dense patches ("Dune mats") that hold the dune together.... Then shrubs can develop.

You aren't on earth (you're okay with the supernatural), so it would be easy to handwave that on this world, the types of plant that would work, don't exist, or died previously.

Maybe they never evolved. Maybe a past civilization genetically engineered a "better something" or an improved something else that accidentally led to.a chain of events that killed off all plant species with certain features, leaving the deserts as well as everywhere else, bare of them. Could be some part of biology needed just got wiped out, could be parasite ecosystem or defences, could be ability to absorb nutrients. Food production and other plants unaffected. (That makes quite a strong and topical backstory, fwiw, and explains nomadism too). Maybe predators ate them, infections got them, or they were overgrazed till they died out.

(Note - my gut feel is that overgrazing seems unlikely to fully destroy them, so its mentioned for completeness. Maybe it accelerated things, as the plants dwindled, those remaining because more needed for herd fodder?)

You don't seem to need much. You need plants to.simply not exist that tolerant sand burial, or strong winds; or plants on this planet spread by spores or seeds to form individual spread out individual plants that can't stabilise sand, not by growing their ground level roots or rizones or other mat-like structures.

Earth was like that for quite a while (grasses are quite a late-comer, and I haven't researched other plants in the Wikipedia article but I suspect the same applies - they could simply not have evolved, or have died). So both different flora, and/or accidental or natural loss, would cover it easily.

Without suitable plants, fences are useless anyway, and if the only wood is from fruit trees near water sources, nobody in their right mind will chop them down for wood, and the occasional fall or imported wood from a trader, will be too low level or costly - and would get buried quickly anyway

Answer 4

When the plants roots grow too much they reach the polluted underground and they die, but before they pump part of the pollution to the upper layers. People don't know why, but they see that if they stay in the same area for too long everything begins to die and they must move.

Answer 5

It is simply impossible to have moving dunes with buildings, soil and plants on top of them. That's because dunes do not move as a whole, they move because the dominant wind is constantly pushing the sand on top of them forward. You can say that the wind move them grain by grain.

If you plant something on top, you will stop the dune... or the sand will cover ("swallow") whatever you have there, be it a tree or a building.

Answer 6

Living Dunes

The dunes are not made of sand by tiny living organisms. The dunes move in the same way caterpillar rolling swarms moves or like a moving army ant bivouac. They don't move with the wind but with intent, possibly some kind of feeding migration.

Note your creatures will have to be largely sustained by "mana" or some other handwavium as otherwise the central part of that mass would starve. Actually having them feed on something in the air like mana would also explain the movement as the ones in the rear try to get the the front where the fresh mana is, this constant turn over will create movement as a side effect. we actually see something like this in cooperating animals like penguin, fish schools, grazing herds, they stay together for protection but each individuals is trying to get to the optimal point (front) of the swarm which creates movement of the swarm as a whole.

Maybe much of the center of the mass is the larva. You should probably make the creatures magically tough or strong so the ones on the bottom are not crushed. Maybe the "sand" is actually a hard spherical shell they grow, with holes like a whiffle ball for them to poke limbs out for movement but much of the weight is taken by the shell.

things stay on top of them because they "float" in the mass of living things and are at the same time anchored deep in the mass, and are thus carried on by the mass movement. that way even if the surface of the "dune" is moving the deeper currents act to counteract that force on the stilt buildings.

Perhaps some plants have evolved to stay anchored in the same way and that's where humans got the idea.

Answer 7

Let's postulate a different biology. Instead of plants which are stationary, postulate a different type of organism that takes water, sunshine, and carbon dioxide to produce sugars and oxygen - perhaps a different kind of lichen that can live on top of the shifting sand. Each year, it falls apart and regenerates in a new place. If it can grow fast enough to support other animals living off of it, then you have the basis to build a civilization. Imagine something growing an inch a day. That rate of compounding would be sufficient.

As long as the inhabitants can find a food source, they can live in shifting sands. Something that can grow in that environment would work.

Why don't we have something like that already in our world? Because shifting sands here are in an arid environment. Water holds the sand grains together preventing them from being blown by the wind. Sufficient water stops sand dunes from moving. Sufficient water also allows plants to colonize the dunes. Thus, our planet has not had a situation where dunes had enough water to allow the evolution of such organisms but not been invaded by existing plants. Any place that could have allowed such evolution got invaded by plants.

Edit Add: To keep the dunes able to drift, have alternating super dry and wet seasons. The dunes move during the dry season. The inhabitants store up food and water during the wet season to survive the dry season.

Answer 8

maybe if you consider that the dunes don't "slowly" shift position but it happens in bursts. So whatever happened before, we now have raging recurrent storms that regularly pass, and typically grabs the dune and shifts it by a couple meters (shifts sand from the wind facing front to the back).

Since the storm always comes from the same direction, waiting out the storm is a matter of orienting the house openings correctly, but there is no fighting the movement of the sand, the storm rages it does not care about barriers or plants on the windward side, and anything on the other side gets buried by the storm.

Answer 9

Maybe they want to travel? It takes decades, but there is no safe alternative.

They build a big dune on the north side of the west coast, where the winds blow to the east. It would take the wind a thousand years to roll it across the continent, but the people nudge it along much faster.

And people on the east coast build dunes in the south, where the wind is westerly. This is the only way to keep trade flowing across the thousands of miles of deadly wasteland that separate them. They start preparing to celebrate a "dunefall" as soon as an incoming dune appears on the horizon.

Answer 10

It's not About the Dunes

The actual hard question is: how does a society survive in a land covered in sand? They need to eat.

Maybe we can find a way to eat that requires the society to drift with the sands...

Sand Creatures

Pick some creature that lives beneath the sands. Maybe Sand Worms, in a nod to Dune.

This creature move very slowly through the earth, and somehow produces a resource that the desert dwellers can use to create food.

It could be that the Sand Worms produce actual soil and that after a few years of use it is covered by sand or exhausted.

It could be that the Sand Worm waste is edible to some other creature that the desert dwellers herd.

Whatever the resource, the desert dwellers follow the slow motion journey of the Sand Worms across the endless wastes. They don't stabilize the dunes because... why would they? They have to follow the Worm to eat.