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I'm working on a earth-like planet with a much lower sea level (like 3000m so the mid-ocean ridge would form many islands) but is that even possible? Will the emerged ridge make some weird stuff and won't it prevent normal plate tectonics?

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    $\begingroup$ Welcome to Worldbuilding, Jean-Abdel! If you have a moment, please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox (both of which require 5 rep to post on) useful. Here is a meta post on the culture and style of Worldbuilding.SE, just to help you understand our scope and methods, and how we do things here. Have fun! $\endgroup$ – Dubukay Aug 7 '18 at 22:24
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Yes, it should be possible. We even have a modern day example of what happens when the mid ocean ridge is above water level. It's called Iceland:

enter image description here

source:https://www.visindavefur.is/svar.php?id=6852

The magma that forms in mid ocean ridges is mostly derived from dry mantle, so the presence or lack or water on the ridge itself would probably not matter that much. In slow spreading ridges you may see something like the above in Iceland, but in fast spreading ridges you may have persistent lava pools or lava rivers along long stretches of the ridge. May look something not too different from the current Kilauea eruption, since both are basalts:

https://www.youtube.com/watch?v=mSTEXd_mcLQ

What you want to have is water in the subduction zones for plate tectonics, but since those are usually deep you shouldn't worry about not having any water there.

A interesting side effect would be the lack of interaction between fresh and hot oceanic crust with the sea water. This would mean that hydrothermal vents such as the "Lost City" and other will not form, or will be much less common. Some hypothesise that life initially formed on Earth at hydrothermal vents, so this may have wider implications for your world.

https://www.youtube.com/watch?v=rFHtVRKoaUM

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  • $\begingroup$ Kilauea is not a spreading ridge, though. $\endgroup$ – L.Dutch - Reinstate Monica Aug 8 '18 at 5:59
  • $\begingroup$ Thanks for your answer but actually there still would be many immersed hydrothermal events so it wouldn't be an issue. $\endgroup$ – Jean-Abdel Aug 8 '18 at 8:51
  • $\begingroup$ @L.Dutch true. But Kilauea is erupting non-viscous, dry, hot basalts which are not too different from the magmas that erupt in mid-ocean ridges. Therefore, the eruptive style and morphology of the lava flows should be similar. $\endgroup$ – Gimelist Aug 8 '18 at 9:23
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    $\begingroup$ @Jean-Abdel hydrothermal vents, not events. And what would be their heat source? The heat source that's driving the vents on Earth today comes from the magma. But if the magma is now in mountain ridges above the sea surface, you need another heat source to drive the submerged vents. $\endgroup$ – Gimelist Aug 8 '18 at 9:24
  • $\begingroup$ The ridge would be partially immersed hence the hydrothermal vents $\endgroup$ – Jean-Abdel Aug 8 '18 at 21:17

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