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Could you have an Earth-like planet with a crust thick enough to prevent volcanos from forming?

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  • $\begingroup$ As the core cools, volcanism will eventually stop. $\endgroup$ – Keith McClary May 9 at 20:56
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It depends on the definition of Earth-like planet.

In terms of size, density and gravity Venus is very Earth-like, but in terms of atmospheric and surface conditions and its axis of rotation, and period of rotation Venus in not Earth-like.

I will assume you mean a terrestrial or rocky planet similar in size to Earth.

Earth's crust has two subdivision: oceanic and continental. Oceanic crust is between 5 km and 10 km thick whereas continental crust is between 30 km and 50 km thick:

Oceanic: 5 km (3 mi) to 10 km (6 mi) thick and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro.

Continental: 30 km (20 mi) to 50 km (30 mi) thick and mostly composed of less dense, more felsic rocks, such as granite.

Earth's crust is fractured into plates as described by plate tectonics. The boundaries of some plate collide causing uplift in the collision zone. The Himalayas is an example of such a zone. At other boundaries one plate subducts underneath the other plate. It's at these boundaries that most of Earth's volcanoes form.

For plate tectonics to occurs large amounts of water must be present to lubricate the subducting plate. The implication of this is that for plate tectonics to occur large oceans need to be located near subduction zones.

The other type of volcanoes that can occur are intraplate volcanoes which are located far from tectonic plate boundaries in the interior of tectonic plates. Such volcanoes are thought to arise from mantle plumes.

Earth has a diameter of 12 740 km, and Mars has diameter of 6780 km. The crust thickness of both planets is 5-50 km for Earth and 10-50 km for Mars. The ration of maximum crust thickness to diameter for both planets is 0.003925 for Earth and 0.007375 for Mars. The ratio for Mars is nearly double that of Earth, yet the Olympus Mons volcano on Mars is larger than any volcano on Earth.

For volcanoes to form, the temperature of the magma must be high enough to melt a hole through the crust and the pressure within the magma chamber must be high enough to overcome the resistance to flow posed by the friction of walls the volcanic vent and the gravity of the planet.

All terrestrial planets will experience volcanism at some period during their formation, it is a matter of when volcanism stops and why. Volcanism on Mercury ceased early due to the planet contracting early in it formation. Even the Moon experienced volcanism.

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Depends on how Earth-like you want it to be. On Earth, most parts of the crust do not support volcanoes. But because we have active plate tectonics, there will always be places where plates slide beneath each other (subduction zones) or where they slide apart. Volcanoes are unavoidable in these locations, I think. A planet without plate tectonics could be volcano-free, but perhaps not for the entirety of its history. Mars has no active volcanoes, but it used to; it's lost much of its internal heat since then.

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    $\begingroup$ Plate tectonics are no pre-requisite for volcanos. Plumes are much more stable than the plates themselves. You see that nicely in volcano chains like for Hawaii or the Kermadec island chain where the plates move over the volcanic hot spot. Crustal volcanism is only one kind of volcanic mechanism. $\endgroup$ – planetmaker May 8 at 9:05
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    $\begingroup$ Sure, I was just saying that if you have plate tectonics you're going to have volcanoes. $\endgroup$ – Kristoffer Sjöö May 8 at 9:54
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    $\begingroup$ Your post start reads the reverse though (at least to me): "most parts of the crust do not support volcanos" can IMHO only be understood that crust is a prerequisite (unless you refer to isostasy - but that'd be quite beside the point of the question). $\endgroup$ – planetmaker May 10 at 6:12

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