Talk:Seafloor spreading

Ocean growth

I think that the ocean in fact does not get bigger because of plate tectonics. If the magma spreads the plates apart and creates more oceanic crust, then the oceanic plates will just go below other plates and the ocean will get new crust and lose old crust. I do think, however, that the land masses will get bigger from the rifts on the land and the land plates will go over all the oceanic crusted plates. User:65.74.253.34

• Quite right - the rate of new crust formation at mid ocean ridges must be balanced by subduction otherwise the Earth would have to grow. The history of the formation of contintal crust is currently an area of active research. However, I think it is fair to say that, over the Earth's history, the area of the contintal crust has grown. For example, volcanic island arcs have formed in the ocean basins and moved towards subduction zones where they are accreted to the continent forming new continetal crust. User:Andreww
  • Formation does not have to be balanced by subduction. For example, folding can shorten length, either of ocean material or by raising the Himalayas instead of quietly subducting India. Continental plates may get subducted rather than oceanic, thus more ocean. There are many factors, such as erosion filling the Gulf of Mexico. Also, perhaps "ocean getting bigger" is not correct if one uses Iceland as being part of spreading — there crust grew to the surface and although there is spreading it may make more land rather than making more oceanic crust. (SEWilco 09:56, 5 Apr 2005 (UTC))
• Correct, the ocean as a whole does not get bigger, but the pacific ocean is shrinking. This is because there are more subduction zones than ridges around the Pacfic plate. This is balanced by the atlantic ocean, which is growing as fast as the PAcific is shrinking. -Anonymous

The Earth can't get bigger due to subduction zones that destroy the older rock, so you are indeed correct that the ocean floor does not get bigger. It's almost like two steps forward and two steps back.

• I understand the prinicple of earth remianing the same size due to subduction, formation, etc. However, something has always baffled my mind. As with water, when it cools, and freezes, the volume of the water expands. Do the materials that earth is comprised of, follow a similar pattern? Because with the theory that earth is "cooling off" this would imply that the volume of earth will infact change over time. Emilyjane 22:25, 24 March 2006 (UTC)
  • Water is unique in that there is no other known substance that expands when it solidifies, so the Earth wouldn't be expanding due to cooling. Every second the Earth is bombarded by billions of particles and meteorites, increasing the mass of the Earth. At the same time, the Earth loses gas molecules from the upper atmoshpere all the time. The percentage of Earth's total size that any of these changes represent is negligible, however.—WAvegetarian•_{CONTRIBUTIONS}^TALK• ^EMAIL• 05:49, 27 March 2006 (UTC)

I agree with a guy above me.Vinaq 19:57, 6 March 2007 (UTC)Vinaq

Yes, it maybe true on the part that it may be a cycle so the earth would not get bigger, however, it doesn't really answer the question given by Emilyjane. If that is so therefore in the future the ice that has been melted would not contribute to the volume of water in the earth? it is 70% water and only 30% of land mass, would that percentage increase? vahn_dinio 10:25, 15 May 2008

Depends on many things. The ocean levels were recently over 100 feet lower, but it's hard for them to rise 100 feet above the current level because shallow seas on land so greatly expands the volume to be filled in order to rise. Ratio calculators then have to decide how much salt marsh is to be counted as ocean. The ratio hasn't changed recently because it takes a long time for continents to grow or shrink, and even a depleted ocean still fills the ocean basin once it falls off the continental shelf.. -- SEWilco (talk) 04:45, 14 May 2008 (UTC)

Cleanup

Is it just me, or is this hard to read? I think it needs cleanup, but I need approval before the stamp goes up. -Anonymous

Passive upwelling caused by subduction

I finished my geophysics degree almost 10 years ago but at that time we were taught that the driving mechanism was the weight of the subducting slab pulling the oceanic crust along. The magma coming up at the mid-ocean ridges is described as "passively upwelling". I am quite surprised that this article mentions there is still some debate over the mechanism of sea-sloor spreading. Is this really so? Can smoeone point to some recent papers on this matter? The arguments I heard 10 years ago seemed quite compelling but beyond old university notes I can't really give any sources. To me, the obvious problem with magma forcing itself out is why would this push the plates sideways? Would it not just pile up on the ocean floor, a la hot-spot island arc volcanoes? One would also need a driving force to push this magma up and none has yet been identified, to my knowledge. As an aside, I also recall how there was some theory that magma plumes in the Earth's mantle were caused when a down-going subducted slab hit the Earth's outer core. Again, this is only a tenuous theory and I can't back it up.Robruss24 (talk) 16:47, 29 January 2009 (UTC)

Huh - I thought I had fixed that here, must have been another article. Slab pull is definitely the dominant mechanism. I'm not sure about the plumes triggered by subduction theory as plates are 2D convection and plumes are 1D convection... but I haven't read about it either. I will fix, then find a source. Awickert (talk) 20:22, 29 January 2009 (UTC)

Just a thought: so what drives the Mid-Atlantic Ridge? it's a passive margin on both sides, so I can only think it would be related to subduction processes elsewhere on Earth or something about supercontinent break-up. Awickert (talk) 20:27, 29 January 2009 (UTC)

That is the problem with only using slab-pull as your driving force. Ridge-push is still AFAIK regarded as a subsidiary mechanism, but in the case of the Atlantic is may be dominant, helping to explain why the spreading on the mid-Atlantic ridge is relatively slow. However, due to the lack of subduction zones around the edges of the Atlantic, the full picture means that the other margins of the plates involved have to be considered. That's OK in most of the Americas, but for Africa, which is itself extending internally, it's a bit more difficult. I don't think that there is 'an answer' out there at the moment. Mikenorton (talk) 11:24, 30 January 2009 (UTC)

From what I know, although ridge push persists in textbooks, it's been taken out of consideration for a while now. I'll qualify the slab pull statement with an "active margins" clause. I think the "best answer" is from mantle plumes, and mantle response to the conductive lid of the continents over long periods of time, which can be linked to continental rifting and cycles of supercontinent creation and break-up... but I think the ultimate jury is still out. Awickert (talk) 18:01, 30 January 2009 (UTC)

The problem is that although the section is titled Search for a Mechanism and Debate, neither of these things is at all discussed; rather one mechanism is posited, unqualified as to importance, as the mechanism. As noted above, it was qualified somewhat with the "active margins" clause, but no context for active margins is given.

There does, in fact seem to be debate on the mechanisms; ridge push is not discussed, neither how it is thought to work, nor the reason it is not currently considered the greatest factor in the movement rates. It is, however, a factor and should be discussed, if at least in terms of the 'debate'. As I understand it, basal drag has traditionally been considered a considerable force, too. In fact, unless I understand it incorrectly, Hess considered this force to be what caused rifting in the first place because of the force that a laterally moving convection current exerts upon the crust.124.171.62.71 (talk) 08:58, 26 August 2014 (UTC)

Observed on any other planet?

This process (without a sea) appears not to occur on any other planet or moon in the solar system. [See section 9 of Plate tectonics]. Is that worth mentioning? --Tediouspedant (talk) 23:04, 6 March 2010 (UTC

There are no pictures of geysers on Europa. So it appears not. I've seen no evidence of plates on the moon. I've seen no evidence of plates on earth, only earthquakes - which could just as easily by tidal forces on land. Why is this a thing?

Why is expanding Earth ignored?

Earth expands... sea floor spreads... continents move further apart... continents flatten... intra-plate earthquakes... d'oh! It's sooo obvious but too hard to go back and admit plate tectonics is shite! — Preceding unsigned comment added by 202.162.74.172 (talk) 06:45, 24 August 2011 (UTC)

See our expanding earth article, which explains why it's regarded as very much a fringe theory today. Mikenorton (talk) 07:12, 24 August 2011 (UTC)

Clarification needed in the lead

In the lead we find this phrase:

The theory is well accepted now, and the phenomenon is known to be caused by convection currents in the plastic, very weak upper mantle, or asthenosphere.

It is not clear to from the text in the lead if convection is happening in the asthenosphere it self or in the mantle under it. For me it seems more likely that the astenosphere is the boundary layer between convecting mantle and rigid lithospheric mantle. That part of lead does cite a 1971 paper, I would suspect there are newer sources that are more clear and assertive on the subject.

—Lappspira (talk) 00:15, 2 October 2016 (UTC)

I have looked at some recent sources and, currently, two proposed models are in favour, each with good points and problems. One model postulates that convection occurs in the asthenosphere only. The other model postulates convection throughout the entire mantle. Therefore, I agree that the sentence in the Introduction section that you have tagged with "clarification needed" does need further revision and more recent sources. I can try to revise the text of this article as soon as I have enough time. GeoWriter (talk) 22:36, 3 October 2016 (UTC)

half-space model

Because this section deals largely with mid-ocean ridge depth profiles I suggest it be moved to the mid-ocean ridges article. BrucePL (talk) 19:10, 29 March 2018 (UTC)

Unlike Bruce I'm not an expert in this, but it seems to me this is supposedly a (very rough) model for the global profile of the ocean floor, not only for the profile of mid-ocean ridges. If this is so, it should remain here. Correct me if I am wrong.

Anyway if it will be moved, perhaps at least a link to this model should appear in the current article. As for myself, as far as I remember when I looked (a few years ago) for a model of ocean floor level, I looked at the current article, but found none - that's why I dove a bit to the subject and added the model here. So it seems to me a place where other people will search for this info as well.Dan Gluck (talk) 19:49, 29 March 2018 (UTC)

@Dan Gluck: Great Dan! We made contact. Thanks for placing the half-space model in the article. I've yet to take on the challenge of editing equations. About the Move: Consider that Seafloor spreading is a process. Mid-ocean ridges are features that result from that process. The morphology of a MOR can be explained by heat flow models like the half-space model. The half-space model doesn't explain SFS. BrucePL (talk) 15:24, 30 March 2018 (UTC)

@BrucePL: Hey, sorry for late response. You're right. Feel free to move it to MOR article. However, this model can still be used to assess to velocity of SFS according to sea floor morphology, so consider mentioning this in the current article in this context. Dan Gluck (talk) 08:51, 7 April 2018 (UTC)

@BrucePL: Until you decide otherwise, I have added a "see also" to the Mid-ocean ridge#Morphology section.Dan Gluck (talk) 16:18, 20 April 2018 (UTC)

@Dan Gluck: Thanks Dan. Sorting out my workload now. Thought about placing the half-space treatment in a Notes section in MOR with text directing to it. What do you think? BrucePL (talk) 19:18, 21 April 2018 (UTC)

@BrucePL: Usually equations, theoretical considerations, models etc. are placed in the text itself, not in a notes section. I think it's better just to have another section about that on that article.Dan Gluck (talk) 13:20, 23 April 2018 (UTC)

@Dan Gluck: Good grief! Has it been over a year since we corresponded about this? I just did a bunch of edits on the MOR page and was reminded of the half-space chat we had. I'll set about copying the model to MOR with a link on SFS article to the model section on MOR. BrucePL (talk) 16:46, 17 September 2019 (UTC)

@Dan Gluck: I expanded this section to add content on the cooling plate model that explains ocean depth and heat flow. I left out the math, which is long and daunting algebra. Some colleagues have suggested that the cooling models might best be their own article that are linked to MOR and SFS, Thoughts? BrucePL (talk) 21:58, 22 November 2019 (UTC)

This section is now on its own page Seafloor depth versus age. I will do some consolidating of this section and delete the math because it is now on its own page. Links on this page will direct reader to the details on the new page. BrucePL (talk) 00:05, 31 January 2020 (UTC)

@Dan Gluck: Dan. Take a look at the new page and tell me what you think. BrucePL (talk) 00:08, 31 January 2020 (UTC)

@BrucePL: Hi Bruce sorry for late response. Seems great. I would love to look at this other model and elaborate a bit more on its results. Dan Gluck (talk) 16:59, 20 September 2020 (UTC)

What does determine the direction and drift of lithosphere plates ?

What does determine the direction and drift of lithosphere plates ? And what does give the force to move the plates and what is a reason that somewhere arise a knew Rift ? So what is the reason, that somewhere the lithosphere-plate is heating up ? I would say it's the Mantle Convection, but the german Wikipedia says, it's not that. it's the weight of the plates. I think that's not true.

Sorry for my english. — Preceding unsigned comment added by 2A02:1203:ECBD:A300:5D01:CC46:C2D6:57D2 (talk) 07:37, 31 October 2018 (UTC)

WP:SPLIT for Seafloor global topography

I worked on this section adding the cooling plate model for seafloor depth (and crustal heat flow). I suggest that this topic be made its own page and creating short content on the Seafloor Spreading (and Mid-ocean ridge page) that directs a reader to the new page.

My thinking is that the derivation of the cooling mantle model is fairly advanced; it includes solving partial differential equations, not usually encountered in WP STEM pages.

The derivation is useful, however, as it includes fundamental principles of solving differential equations by setting boundary conditions and approximations.

Thoughts anyone? BrucePL (talk) 19:45, 26 November 2019 (UTC)

plate tectonics is in fact also driven by convection, but one that includes the crust itself as well

The physical phenomena of convection includes any case where in one part you have hot matter that ascends, then cools down and goes down in another part. When it is not driven by the temperature difference it is called forced convection, but it is still convection. Anyway, as far as I understand, plate tectonics is in fact driven by temperature differences, so it is a regular convection and not forced - this is true whether it is driven by slab pull due to the margins being cold (after cooling down) or by ridge push due to hot material ascending from below, or due to mantle convection (with the latter option probably not true).Dan Gluck (talk) 18:35, 25 September 2020 (UTC)

Images of plate tectonics 129.232.73.108 (talk) 20:25, 24 January 2024 (UTC)