My apologies for the extra long title, so let's get to the point. There is an Earth-like planet with a very dry personality. Six to ten percent of the surface is water, averaging in at 30-100 meters deep. In turn, 79% of the dry land is salt, suggesting that this was once a waterworld but, due to migration, got right to the inner boundary of the habitable zone and as a result lost most of its water.

With such a near-absolute exposure to air, would the plate tectonics act any differently from those on Earth, a planet in which water makes up the majority of the surface.

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    $\begingroup$ Does this answer your question? How much surface water do I need for plate-tectonics on a planet? $\endgroup$ – rek Sep 10 at 2:45
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    $\begingroup$ @rek I think the other question is more about a minimum water threshold for plate tectonics to exist (which I think should not be a thing), while this is about the effects of having less surface water on existing plate tectonics. $\endgroup$ – The Square-Cube Law Sep 10 at 3:31
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    $\begingroup$ @Renan You are correct. $\endgroup$ – JohnWDailey Sep 11 at 0:34

The plates will move slower.

Some observations from Plate Tectonics Driving Mechanisms: Some Simple Rules that Explain Why the Plates Move the Way They Do by Christopher Robert Scotese, Northwestern University:

  • Oceanic plates move faster than continental plates.
    • Oceanic plates tend to have ridges (pushing) and attached subducting slabs (pulling).
    • At the base of oceanic plates in the LVZ (low velocity zone), a region of partial melting that provides "lubrication" at the base of the plates.
  • Plates with a large area of continent move slowly (e.g., Eurasia) because they have a deep continental keel connected to the mantle.
    • For this reason continental plates are more likely to be affected by mantle flow.
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    $\begingroup$ This is a logical start, but without a confirmation by a geologist, I'd take it with a grain of salt. The link is only an outline of generalizations without any of the supporting details that help us understand why the generalizations are accepted. In other words, these observations may have nothing at all to do with water, but rather reflect the nature of the crust where water does and does not gather. In which case the lack of oceans has nothing to do with slower plates - just the thickness and anchoring of the mantle. $\endgroup$ – JBH Sep 10 at 2:54
  • $\begingroup$ It is true the plates will move slower but nothing else in the answer is correct, the linked paper is full of problems. for a start the idea that spreading centers can push plates has been thoroughly disproven. The idea of a continental keel reaching the mantle is also hypothetical at best. $\endgroup$ – John Sep 10 at 23:42

The plates will move slower

Assuming by less water you mean less oceanic crust, tectonics will be slower, continetal plates generally move slower. Oceanic plate is thinner and lighter than continental plates and thus can move a lot faster, it is just basic physics the same force can move a lighter object faster. In addition continent to continent boundaries suffer from a lot more resistance and end up moving slower since continental plates cannot subduct under one another. This also means such a planet should be a lot more mountainous. It is not coincidence the largest mountains on earth on one continental/continetal boundaries. but at the same time it will have less volcanoes since volcanoes arise primarily from subduction. Expect high turnover on seafloor, which means the volcanoes you do have will be larger. So fewer but larger/taller volcanoes/volcanic ranges.


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