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From reading the novels, the impression is that Dune is like a vast ocean of sand, with the sandworms akin to gigantic sea-monsters, only in sand. I can't remember any specific mention of how deep the sands are, though. They'd certainly need to be quite deep to accommodate some of the very big worms, and it is said that the sandtrout can go deeper still.

Here on Earth, although desert depth is hard to measure, it is said that the Sahara is up to 40m deep, although deserts far into geologic history can have depths of several hundred meters. Then again, the sandworms aren't exactly physically plausible, so speculation based on the real world will only go so far.

How deep are the sands on Arrakis? Is there any direct or indirect reference in the books, or any notes?

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    Not an answer, but note that the Sahara is a very recent desert, so probably shouldn't be expected to have deep sand. Oct 7, 2014 at 8:58
  • there at least deep enough, for worms, but we also know that the planet was able to be returned to a "normal" type planet similar to appearance to earth after about 3000 years of the reign of the God emperor. should the entire plannet have been miles deep of sand that is quite a feet as they would have taken sand off of the planet and then replaced it with soil to make things verdant. i always assumed the deserts were similar to the sahara, as the planet became a sand planet again within about 1000 years after the god emperors death.
    – Himarm
    Oct 7, 2014 at 13:05
  • @Himarm - They were using deep-rooted grasses to "fix" the dunes into place.
    – Valorum
    Oct 7, 2014 at 17:45

2 Answers 2

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There's no canon confirmation of the average depth of the sand. The sole indication seen in the original Dune novels are from the death of Liet-Kynes where he narrates the pre-spice mass forming below his feet:

"only a hundred meters or so beneath him; a worm sure to come, but no way to trap it on the surface and use it.".

He goes on to describe this as

"deep in the sand"

but whether he's indicating that it's near the bedrock (e.g. in the same way that we might describe the "depths" of the ocean) is wholly unclear.

Later on, we see that the Fremen have been building sand-dunes that are truly enormous in scale:

With the downwind face anchored, the windward face grew higher and higher and the grass was moved to keep pace. Giant sifs (long dunes with sinuous crest) of more than 1,500 meters height were produced

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If you take a realistic scientific approach then there is a maximum depth that the deserts can be.

When sand deposits accumulate they undergo a process called diagenesis, which involves physical and chemical changes in sediments first caused by water-rock interactions, microbial activity and compaction after their deposition. Increased pressure and temperature only start to play a role as sediments become buried much deeper in the Earth's crust.

During the process of diagenesis porosity of the sediment decreases.

The early stages of diagenesis can take place a depths of tens of meters.

As the sand undergoes additional compaction resulting from further accumulation of sand, the sand comes under increasing pressure from overlying sediments. Sediment grains move into more compact arrangements, ductile grains (such as mica grains) are deformed, and pore space is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution. Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact.

Mechanical compaction takes place primarily at depths less than 1,000 meters. Chemical compaction continues to depths of 2,000 meters, and most cementation takes place at depths of 2,000–5,000 meters.

So you can assume that even if the bedrock was down below 5000 meters the geological processes that turn sand into rock/stone would make the depth of the desert on average about 3000 meters deep.

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  • You seem to be describing the processes that take place on Earth (water-rich, volcanically active, etc) and not the barren wastelands of Arrakis.
    – Valorum
    Jul 24, 2021 at 14:12
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    You would still have the effect of pressure from the sand above forcing the sand to become a hard solid layer, This would probably result in a deeper bedrock but still the sand would from a solid layer
    – Richard C
    Jul 24, 2021 at 19:04
  • I spotted a weasel word in that sentence. Perhaps it might probably act this way :-)
    – Valorum
    Jul 24, 2021 at 19:06
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    physics is still physics, the higher pressure any substance is put under the hotter it gets and that heat then changes the physical makeup of the substance.
    – Richard C
    Jul 24, 2021 at 21:12

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