Subduction - how we know
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- เผยแพร่เมื่อ 7 ก.พ. 2025
- Subduction is a fundamental Earth process, a cornerstone of plate tectonics. It's why the "Ring of Fire" exists - and is responsible for major geo-hazards - volcanic mega-eruptions, devastating mega-thrust earthquakes and associated tsunamis. But how do we know it happens? Follow how geophysicists found and identified subduction zones - and how nowadays we can image them, penetrating deep inside the Earth.
This video was first published to sit alongside the fourth season of the BBC's "Race Across the World" and forms part of The Shear Zone TH-cam channel.
#ringoffire #tectonics #geology #earthquakes #subduction #indonesia #geophysics
Great presentation! I’m relatively new to learning about Geology but I’ve been a pretty deep dive on what’s available online. The one thing I do notice though is that there is a lot of misinformation about the driving force behind plate Techtonics. Your explanation about subduction being the motor of Techtonic motion, I.e Slab Pull is well explained in your video. It kinda drives me crazy how MOST videos still point to Convection as being the driving force, and not as a product of subduction.
Prof. Rob has incredible clarity and the ability to simplify complex observations.
I've been missing your content, so this is refreshing. Thanks Professor.
Three new videos today. If you've not been following along - the Ring of Fire series has a whole stack of films on the geology and tectonics of E and SE Asia.... Check out the Shear Zone channel home-screen.
I never knew how controversial it was to talk about plate tectonics till I read these comments.
Indeed... there are some curious ideas of there - at odds with basic geophysical observations/deductions....
This is excellent, Rob.
Useful explanation - thank you.
This content is top notch!
thank you - glad you enjoyed it!
Great video as always, Rob. Thanks for the history and science
Thank you - glad you enjoyed it!
I find all your videos fascinating.
Thanks!
Traveling north from the Gulf of California in Mexico, there is ths Salton sea, then the San Joachim valley and further north, Tomales Bay. These crustal depressions represent a failed rift. The sense of movement along the San Andreas fault is strike slip as it meanders along this failed rift. There is nio evidence of subduction.
The subduction hypothesis was floated a decade before Marie Tharp's map of the ocean floor was published and is at odds with the evidence of global expansion. Yes, continents have moved away from one another but none have collided. Zones of 'subduction' are much more likely to be zones of obduction. Amazon sells magnificent copies of Tharp's map in a 36" x 24" (900mm x 600mm) format, displaying breathtaking detail.
Thanks for your reflections. The length of California is of course in transform mode (the earthquake focal mechanisms tell us - and its evolution was worked out by Tanya Atwater at the dawn of plate tectonics). Plenty of old evidence of former subduction (e.g. the Franciscan).
I have (original print) copies of Marie Tharp's revolutionary maps - but these are not so great at representing trenches (see the SW Pacific for example) not least because these areas were highly sensitive to the US Navy... The increase in knowledge of our planet has increased somewhat in the past 60 years... I've tried to introduce some of the highlights in the Subduction video - but there is a huge base of fundamental data out there now. Arguing against subduction is not far off arguing that the planets orbit the Earth.... a bold move.
Excellent explanation and level of detail, an instant follow, thank you.
thanks!
Excellent piece!
Very clear research, great illustrations an excellent delivery. This is a classic!
Thank you so much, especially for the correllation on seismic tomography and computing power. Very clear and amazing.
O presume this was the method used to identify the two "blobs" of what once might have been Thea under Africa and the pacific ocean that have been reported recetly?
Yes - its essentially seismic tomography. Though whether these LLVPs are bits of Theia is debatable!
@@robbutler2095 Is there another explanation for the rise of the LLVPs into the mantle?
You have a graphic error with ‘ones’, which should be zones.
Love all your videos.
Great video! I like the perspective
thanks!
I have been looking at that area for a long time now. I love Google Earth. I can see so much like this. I call them crowns, and they look dangerous to me. Thank You for showing us. I had a feeling it was like that under there.
I like expanding earth theory for the general continental movements still, as the sea floor ages match that way. And other things similar to this for localised changes.
We can rule out any significant expansion of the Earth's surface from palaeomagnetic measurements (which determine palaeolatitudes) through time. If the Earth expanded then N-S distances on the ground in the middle of a plate (e.g. Africa for the past 300 million years, the time scale for the sea floor spreading recorded directly in oceans) while fixed would show a shrinking distance from the distance in latitudes. Doesn't happen. Also - by what physical mechanism would drive expansion? Sorry - the idea has been well and truly debunked.
Greetings from the BIG SKY of Montana.
Thanks a nice video, however a massive subduction of this kind is extremely unlikely at least in the well known form in which it is presented and taught in most colleges. The problem is that it could be interpreted completely in other way, they are just the slabs from the ancient "continental" crusts in different orientations mainly under the Pangean pieces (and previous slabs form resurfaced crusts from the prior times) that form the now continental floors (or exist beyond them), and there are many misfittings with "subduction ideas" when you look to world´s examples. The occurrence of the seismic activity prove just that contact and stress is being released in the interface between the plates, they hold each side, they have friction, the plates did move laterally as a result of planetary expansion and changes in isostasy through time, and thus the tomographies do not prove beyond reasonable doubt any massive horizontal subduction. The process is also impossible, how lighter materials will sink into heavier and denser ones? What force will push them so massively under even more lighter continental slabs and where are the scars of the stress that such a massive collision will cause on the allegedly conveyor belt in the oceans? It just is absent, major failures are perpendicular to the rifts and some parallel features occur along the main ridges but none of them are clear near the "massive subduction zones". Both ideas are well established in the mainstream geological scheme while being mythological and against the laws of physics. Some vertical subduction do happens and lithospheric leaks do sink continental pieces, you can observe it in some places on the continental emerged areas, and in Zelandia. I had seen many seismic tomographies and look at many papers and it clearly seems that facts are being forced into these failures of the mainstream tectonic theory by dogma and academic inertia. Theories sometimes drives the research and genial ideas sometimes take a long road in order to be accepted and widely recongnized. As many are convinced of it happening (massive subduction and conveyor belts), they interpret observations in a wrong way, it is a mischieving auto maintaining circle. Now consider the thickness of the plates involved, many cases are in the ratios of 1:12 which would be already strange enough, but we have deep continental roots and thicknesses of 1:47 in some areas of the Andes, for instance. That means that a thin oceanic crust of 11-28 km at the best, is expected to curve itself and go down about 350-650 kms to go under the continent for unknown real reasons... How will a thin layer will collide with such a massive wall and swiftly move beyond it? Ancient resurfaced slabs of prior continental-planetary pre-oceanic-expansionary are a much better explanation for what we can see in the tomographic and seismic data. For if it isn´t enough to consider those ideas, we have the ages of the sea floor “precisely telling the story of how all the sides of the chronological floors met each other” and when removed carefully in corresponding ages in smaller globes we arrive to the hard truth and fact that all the edges of the continents (which are just pieces of the Pangean time crust opened by the new oceanic ridges and ocean floors) match each other at 99% precision. James Maxlow from Curtin published a brilliant PhD Thesis reconstructing all the fitting and giving a wide range of other hard proofs on several scientific fields some 28 years ago. The proofs ensembles well with Croizat´s biogeographical ideas, panbiogeographic tracks and nodes, biogeographic patterns in Gondwanaland, biodiversity resemblances, rock match-correspondances in correspondent continental sides, geological formations, the worlds hydrocarbon doughnut (pre-mesozoic, mainly late Paleozoic doughnut on then tropical areas), and even geodetical data. Once you realize the amazing match, it result unnecessary to think about massive horizontal subduction mainly because it will directly contradict the match and it goes against physics, and also, the later (expansion matches) are so real and overwhelming that I find difficult to understand the slow rate of acceptance of the whole idea and the facts behind it. It is even a well distributed phenomena in the Solar System and had been mapped in Ganymede and other places, and expansion is also a main feature of the known universe... so expansionary plate tectonics without myths might be a good idea.
M Sc David Brailovsky Mexico City
A key point about subduction is that it's not about crust (oceanic or continental) but lithosphere - the mantle component thereof. This is colder than the underlying asthenosphere therefore it is denser - and, in the subduction model, it this density difference that drives the the down-going slab. Note also that the shallow earthquakes at trenches are thrust-sense - and the measured motions associated with these (e.g. Tohoku) are consistent with these being convergent plate boundaries... and its oceanic lithosphere that's going down... i.e. subduction. There are (and have been) vigorous debates across the earth sciences about all of this that are pretty much resolved by increasing data. I don't recognise your characterisation of the scientific community.
@@robbutler2095 Dear Rob, well it started pretty much about the crust and the upper layers... convection in the astenosphere is real but there are alternative reasons for what we are seeing in the seismic tomographies and the earthquake areas and depths. Many slabs deep inside are almost vertical, then you have more slabs under the continental crusts of course, and they shall not necessarily have to be related to the impossible process... what about the deep roots of South America? Or some pieces of the western Pacific too? What had been always represented is that the subduction has a lot to do with a thin oceanic crust subducting beneath the continental floors, not other way round, that´s what is teached in the universities and you can reach it out easily from plenty of theoric text books on oceanography and geology. Now, even accepting that it could have something to do just with very deep pieces of the litosphere and not the superficial ones explained in most books up to now, you cann´t explain out the perfect match on the sides of the continental (pangean) floors told with chronometric precission by the very ocean floors that had been well mapped and dated. If a substantial horizontal subduction was being taking place as thought by some, then the pieces will mismatch in just a few hundred million years. Facts told another story, sorry. And that is just the tip of a gigantic iceberg of information that also correlates the sides separated during the expansion of this planet, Maxlow explained it awesomely in his PhD thesis 29 years ago and little diffusion for his genial work had come so far, he gave fossil, paleontological, paleostratigraphical, mineral and even hidrocarbon correlations, together with biogeographical patterns and geodetical data that clearly show what is happening. Expansive tectonics are not limited to Earth, they had been sighted in many astronomical bodies in this Solar System, the list is large, and is a property of the Galaxies and the universe. It is highly likely that also orbital patterns expand. Some objects, could contract, but many more did expand. A complete revision will took many many pages, so I will just explain the alternatives for the subduction "proofs" briefly: The seismic tomography are the shapes of the slabs from prior continental expansion resurfacements that preceeded the oceanic expansion in a much violent planet perhaps like Venus now, some of the slabs are even turned vertically in strange forms that do not always fit the "subduction hypothesis", you do not find the same beneath the "oceanic plates", many places in the oceanic areas are quite deep in their earthquakes contradicting the predictions of massive horizontal subduction, the earthquakes occur both by friction between plates (and indeed oceanic type and continental type) after the readjustment of the planetary layers after gravitational forces and electromagnetical forces (less known) by the Moon, the Sun and other large planets in the system (surely Nemesis like, and perhaps some other large bodies, larger than Jupiter that could explain the tilt and orbits of everything in the SS, quite homogeneous and needing something more than Nemesis sister to be explained, a mystery still), and they preserve the matches. Even if the coincidental forms and sizes of the "continental" edges and the chronological story told by the ocean floors is not appreciated in its full implications, you can explain the mountains beside the ocean trenches after perpetuated volcanic activity of the original cracks that developed and allowed Rifts to be formed and resurfacement to be redistributed in oceanic dorsals instead of massive events in changing sides of the planet. The expansive theory explain why you have so little ancient rocks, they are beneath the resurfaced layers that preceded oceanic expansion. Earthquakes also happen as result of changes in isostasy, when the materials are relocated through erosion and volcanism, mass movements and redistribution of water, the interface of the continent-ocean regions change. An increasing weight will pull the trench downwards (but the inverse could happen sometimes, slightly, if the rocks are eroded), and the ancient volcanic faults are quite stable and had not been closed, so the trench get´s deeper. Somewhen the pressure from beneath (call it expansion force, perhaps a good term?) pull them upwards and release seismic energy. Still earthquakes can happen through litospheric drops or leaks where the isostatic equilibria also changes. Some other earthquakes also happen through innerland faults and the redistribution of tensions and compressions all around. In the changing equilibria you can find many components and impact craters surely also got their place there, together with the not well known features of the Solar System I quoted before. Strangely and corresponding to many other planetary features in the system (and planetesimal ones), the attraction is also toward the south. It´s not coincidence, of course. Now, traditional mainstream tectonics could not explain well the Aleutian Trench where the movement is bizarre and not well oriented toward the volcanic arch as expectable or the mid South Atlantic perpendicular trench wich is better explained by changes in the isostatic forces and the balance within compressions and tensions. I think that most massive horizontal subduction is indeed much more a myth than a reality and that it is an unnecesary myth by the way, since everything could be well explained by expansive theories. Finally, the corrugation of the Earths (and other planets and moons) through the increasing diameter is a major causal force creating orogenies, it crack the lower part of the plates and the continental floors (which are thicker) and compress the upper parts causing vertical subductions and changing the isostatic equilibria everywhere. Rock abundances through Earth´s history also fulfill the expansionary view since little sedimentary rock is found before the oceanic expansion started and most rocks of the pre-pangean history are volcanic, or metamorfized from them... a planet with smaller surface will certainly harbor much deeper seas, perhaps comparable to those in Europa, Ganimedes and Calixto, which will create conditions for little erosion and small formation of sediments, which perfectly match the whole scenario. That´s still a tip of the iceberg. Sooner or later a major transformation of geological and biogeographical theories will result from recognizing the amazing clues that the planet give us, an expansionary geology with little or no massive subduction. Best wishes, David Brailovsky / PhD Student / Institute of Biology, UNAM
what makes a subduction zone form? Is it a random thing or are there elements to the process that we know about?
Good question! In the modern Earth (past 100s million of years), subduction zones grow - splitting from existing plate boundaries (or close to them - in back arcs)... But in the deep past (pre 3 billion years ago) - were they more patchy ? An area of active (and at times somewhat speculative) research!
Thanks for the video Prof Butler.
I know this is a question for which we might not have an answer yet, but I wonder what your take is: what was first, the chicken or the egg? does the subducting plate create tension, originating spreading ridges? or do the spreading ridges form first, due to some kind of mantle upwelling, which then pushes denser oceanic plates against more buoyant plates, causing them to subduct?
It is a question that arose as plate tectonics was proposed. Ridge push is an unlikely driver - if ridges were pushing you'd expect topography and its decay from ridges to relate to distance from ridge... (dynamic topography) - but it doesn't, it relates to age (therefore spreading rate). So mantle doesn't upwell dynamically at ridges in this take, it is a passive process - as if the lithosphere is being pulled apart. So the subducting plate essentially pulls the lithosphere... Can also explain back-arc spreading - as slabs sink or migrate, the upper plate rifts... is pulled apart. Lots more evidence too. So for me its all (well almost all) about slabs...
@@robbutler2095 thanks Rob, very interesting.
It makes the breaking of Pangea even more mind blowing to me, then. To think that oceanic plates that were "welded" to Pangea started subducting from different directions, and therefore literally splitting the supercontinent apart.
Which then makes me think that this continental crust from Pangea must or should have broken up along weaker planes. I'm sure we have evidence of this?
@@amacuro There is a question of stability of supercontinents - they're pretty transient things... And some evidence that Pangea break-up - it's sites, was controlled (infuenced) by plumes... which while not driving plates, can condition where plate boundaries go...
@@robbutler2095 thanks for the answer.
I guess if the supercontinent was already subjected to tension from different directions from oceanic plates "wanting" to subduct, the plume events would have weakened the continental crust enough to allow these tensions to cause some actual rifting at those spots; I guess akin to poking a balloon with a needle, but in slow motion?
Playlist link for more videos in this series: th-cam.com/play/PLxvNbEa7Qws7fgAfOIHx9ax9TkTy84rS_.html&si=Ql7sdyreCvgUU0uB
Thanks!!
Question is, does subduction drive plate tectonics, or does plate tectonics drive subduction. Sea floor spreading is clearly not driven by subduction ... so the actual driving mechanism of plate creation and plate destruction isn't subduction (its the result of ... what ... mantle plumes, mantle circulation ... be interesting to hear your thoughts on that.
An area of long-standing discussion - what "drives" plates....
My take (not original - plenty of others have worked this too): The mantle is a convection machine driven by the Earth's heat budget - so has a warmer base and a cooler top (plates). In the modern world about 10% of the heat budget is taken by mantle plumes, the "rest" by plates - chiefly lost through the ocean ridge system. But ridges are not important players in plate motion - they don't push plates - they're pretty passive - so indeed are "pulled apart". Subducting plates are a key driver (slab pull) as the cold lithosphere sinking. Cold "return flow" in the convecting world.... Hope this clarifies my take on this...!
'Wadati' is the awkward pre-war 'Japanese-style' orthography, modern (Hepburn) spelling (and pronunciation) is 'Wadachi'
Thanks for the correction!
There is a major failure in the idea of massive subduction, if it happen (which most probably not) then the edges of all the continental floors will mismatch, (and they match incredibly well), and the ages of the sea floors will not tell how they match but strangely will coincide with the matching even when one must think that such a subduction process would be heterogeneous around the planet and over time. It is simply unnecesary and against the laws of physics to continue to support "the process" (Seek Maxlow letters for instance, he already wrote a lot about the topic). Nevertheless, the convection is a real process and shall have effects in the geological and isostatical interrelationships on the plates. Just the subduction process is mainly vertical, and not so relevant. The relevant processes are inner expansionary forces, the convections and energy interchanges, the inner dinamo, the tides produced mainly by the Moon (large litospheric and astenospheric massive tides), and the other attractions that I suggested in my response to your response (below). Thanks, David
Well made video. However, subduction as it is described by plate tectonics cannot be known because (with all due respect) it is not true; the Earth expanded and does not function under plate tectonics. There are countless evidences that have been accumulated since plate tectonics became the dominant model in geology that are strong proofs that the Earth expanded.
For example, the Ontong Java Plateau is considered to have formed with Manihiki and Hikarangi Plateaus as a single unit near Australia, but this puts the oceanic plateaus far away from South America where, in Ecuador, the Pinon Formation is found which is also considered to have been part of the Ontong Java complex *and* is described as having to have formed *in place*, thus demonstrating that the Ontong Java Nui complex was both near Ecuador *and* Australia because the Pacific Ocean was not yet open in the Earth's expansion process.
Another example is the region of the East Mariana Basin, thought to be the oldest crust in the Pacific, has core samples dated to tens of millions of years *after* (more recently, that is) samples taken from surrounding regions. This is documented in literature and completely ignored, in terms of accounting for it in the narrative of why plate tectonics is true, because it would mean the Pacific plate is not understood.
Then there are enigmatic mountains like in central Australia (Alice Springs) that are described in literature as being unable to be described by plate tectonics as it is currently understood since they are at the center of a "plate" that should be undergoing mountain uplift at its boundary through the Wilson cycle, according to plate tectonics, and not at the center of the plate.
It is very important for us to be able to allow for new evidence to come about without also accepting the dominant viewpoint proposed to explain the evidence, or else we become overrun with a singular possibility being weighed which will always weigh more than an unconsidered second possibility, regardless of which is actually true. Seafloor spreading is a good example of something that plate tectonics has staked claim to, but also is able to fit into expanding Earth models where the same evidence being presented as proof of subduction can be also presented as proof of nuances of the Earth's expansion process. In the case of plate tectonics, continental magnetic anomalies are largely ignored and are never publicly discussed with regard to the model because they are not used as evidence of plate tectonics directly. But these two are inseparably one aspect of Earth and cannot be analyzed separately because one component is convenient and helps give credence to the model while the other is cumbersome and difficult to explain, making it not even come up in any presentation on plate tectonics so that only those who are actively seeking the truth and not just any answer will recognize there is something missing. Others will fall for the partial analysis hook, line, and sinker, and live their whole lives never the wiser.
Because continental magnetic anomalies are demonstrably shaped by current flows that were part and parcel to the Earth's expansion process, namely undercurrents below the crust that first built up pressure below continental shelf of the Earth (making the magnetic anomaly map as we see) and only after its pressures built up sufficiently was it able to fracture the crust and allow for the Earth's internal pressure to relieve and expansion to occur. A good example is the entirety of central Asia has currents that blatantly flowed through it imprinted in the magnetic anomaly map, literally branching off at a triangular wedge shape in Turkmenistan (the size of the country, in fact) where current flows went right and left. There are places where it can be found to have flowed inward in an eddy such as at the Kursk Magnetic Anomaly which was surrounded by current flow paths (including the one through central Asia).
Plate tectonics is only true when it is the only model being considered. Most people know about flat earth theory, which is an easy opponent for plate tectonics, but few know about the expanding Earth theory in spite of it actually being in peer-reviewed technical papers even today (and being the actual reality of the situation tbh).
This is hardly science. It begins with the presumption that the earth has always been exactly the same size, and presumes subduction accordingly.
At no point is there any discussion of the many problems with subduction theory. At no point is it acknowledged that everything here might be explained by a mere bunching of the plate, rather than subduction.
This is the wide eyed repetition of old theories, nostalgic reverence, without any critical thought.
Profesor Rob appears to lack an understanding of subduction processes, and is mistaking block train pulsation tectonic gravity anomaly signatures for a divers springboard 🤭
????
"Jawlogy"
Sorry, but in my opinion we are looking at the wrong way of the working of plates. If science would look as the thicker layer is a magma river running underground in a channel. You could with messurements predict earthquakes. Even higher and lower ate predictable.
I'm not sure to what you are referring. If this is about asthenosphere (all the mantle that sits below plates) then it isn't magma (molten) - apart from tiny patches... it's a viscous solid. We know this from the behaviour of seismic waves - specifically the Earth's ability to transmit shear waves - in all layers expect the outer core. Check out:
th-cam.com/video/nxaLWFNoCV4/w-d-xo.html
@@robbutler2095 Rob, magma is moving in-between tectonicplates. I have a calculation that shows perfect the new high and low. And an earthquake happens because a channel is blocked or has become smaller because of shifting from a plate.
@@robbutler2095 Rob, if you want to know more. Than step away from plates are causing high earthquakes. Remember a year or two ago the rock falling down in a small Swiss village. It did almost nothing on the Richterscale. Magma has matter and anti matter. Crystals the forming and deforming, the power that is being released that is where you have to look at.
@@robbutler2095 Rob, if you take water in a tube and you rock it up and down. You see water turning around. This is what magma is also doing underneath the earthcrust. As 2 channels come together, like in Turkey and Syria last year, then the channel gets cloucked by magma, magma will also increase in speed. (the steam locomotiv sound people are speaking about) as nagma then moves it is creating a vacuum that can let the channel implode. Best example the ripp in Afrika, where we are talking about seperation in the near future. The images just after it happened show a massive magma movement inbetween the riff that had formed.
My brother in Christ it doesn’t work like that and they don’t have to look any further than identify the refractions both the p and S waves generate as they travel beneath the earths crust which allowed us to identify the compositions of both the inner and outer core as a result.
Just say no to subduction. It's immoral. 😂