Subduction - how we know
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- Опубліковано 27 тра 2024
- 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 UA-cam channel.
#ringoffire #tectonics #geology #earthquakes #subduction #indonesia #geophysics
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.
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.
Useful explanation - thank you.
I find all your videos fascinating.
Thanks!
This is excellent, Rob.
Excellent explanation and level of detail, an instant follow, thank you.
thanks!
Greetings from the BIG SKY of Montana.
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.
Great video! I like the perspective
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?
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.
You have a graphic error with ‘ones’, which should be zones.
Love all your videos.
Playlist link for more videos in this series: ua-cam.com/play/PLxvNbEa7Qws7fgAfOIHx9ax9TkTy84rS_.html&si=Ql7sdyreCvgUU0uB
Thanks!!
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?
'Wadati' is the awkward pre-war 'Japanese-style' orthography, modern (Hepburn) spelling (and pronunciation) is 'Wadachi'
Thanks for the correction!
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...!
"Jawlogy"
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).
Profesor Rob appears to lack an understanding of subduction processes, and is mistaking block train pulsation tectonic gravity anomaly signatures for a divers springboard 🤭
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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:
ua-cam.com/video/nxaLWFNoCV4/v-deo.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.
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.