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Ocean trench formation

  1. Jun 14, 2010 #1
    I have a geology question; a subject which I know next to nothing about.
    Regarding tectonic plates, I heard someone suggest that when there is oceanic trench formation, it is always accompanied by mountain/hill formation. The websites I have looked at say that there MAY be mountain formation when there is ocean trench formation, but none that state that is it is inevitably so. Is anyone knowledgeable in this area?
    I would really like to know if these two things are invariably linked.
    Thanks in advance,
  2. jcsd
  3. Jun 17, 2010 #2
  4. Jun 17, 2010 #3
    Here's the short answer

    From Davis, Jr. Richard A.; Principles of Oceanography, Second Edition; Addison-Wesley Publishing Co.; Reading, Masschusetts; 1977; p041 & 42

    Last edited: Jun 17, 2010
  5. Jun 18, 2010 #4
    Thanks Gannet! INVARIABLY was the word I was looking for!
  6. Jun 23, 2010 #5
    Invariably is a dangerous word to use in geology.

    Since trenches mark subduction zones and subduction zones have to be initiated at some point in time, and since volcanism (and island arcs) associated with descending lithospheric plates cannot begin until the plate and its entrained sediments and water reach an appropriate depth, then there should be some trenches that have not been in existence long enough for this to occur. i.e. trenches will not invariably be associated with island arcs. Indeed the absence of an island arc from its expected position adjacent to a trench would be good evidence for the youth of the trench and the recent (geologically) initiation of subduction.

    One promising candidate can be found in the Phillipines. The Cotabato trench lies to the south west of Mindanao. Hamilton (Tectonics of the Indonesian Region, Prof. Pap. 1078, US Geol.Surv. 1979) demonstrated with seismic reflection profiles, confirmed by the dip of the siesmic zone (Cardwell et al, Subduction in the Phillipines and Indonesia, in The Tectonic and Geological Evolution of Souteast Asian Seas and Islands, AGU 1980) that the Celebes Basin is being underthrust to the east.

    There is no associated volcanic arc and, significantly, the inclined seismic zone is very short. Independently these observations suggest a young subduction zone. Together they are strongly indicative. Regardless, here we have a trench with no allied island arc, thus disproving the claim of 'invariably'. If we replace it with 'nearly always, except in the case of young trenches', then we will be nearer the mark.
  7. Jul 12, 2010 #6
    Invariably is invariably a dangerous word to use in science in general!)
  8. Jul 14, 2010 #7
    Thanks for the response Ophiolite.

    Surely not!
    I thought that one endeavour in science was to be able to predict exactly what will happen given a set of 'properties' of a 'system': if you know it well enough, you should be able to know what the outcome will be.
    Admittedly, it's not always true (errors in DNA replication, for example), but I was led to believe, that in Newtonian mechanics at least, if you know enough information, you can say whats going to happen.
  9. Jul 14, 2010 #8
    Well, Newton didn't know much about QED and uncertainty, and even Laplace (or was it Lagrange? I invariably get them mixed up... :devil: ) thought that he could predict or retrodict every state of the universe, given enough precise starting information. (I don't know how much thought he gave to N-body problems!!!) But then he didn't know about chaotic systems, did he? Nor even thermodynamics and information theory.

    And no, science has many aspects and many consequences, but proving things is not one of them. One of them, actually the most fundamental, is the discovery and formulation of hypotheses about the empirical world, and, by means such as analysis, prediction and falsification, to produce enough evidence to select whichever of the hypotheses is strongest in the light of the available evidence. If it is strong enough it becomes a working hypothesis. However, we never, ever, know for a fact whether the hypotheses we have considered include the correct one.

    Right? :devil:
    Go well,
  10. Jul 15, 2010 #9
    Whats this got to do with anything? You almost sound like you're trying to be condescending to Newton (which is laughable!)

    What's that got to do with it? I never mentioned "proving things". I think your just 'one of those people' who has to throw his two cents in.
    Yes, we don't know whether the theory of evolution is absoultely 100% correct, just like you can never truly be an athiest (if your a rational person). What does that have to do with invariably?
    You can predict whats going to happen, that doesn't mean you have to know for a fact what causes it. I could drop a ball and know all the necessary 'factors', and I could say that its going to drop to the ground and predict the time it takes. It doesn;t mean the theory of gravity is true, but it doesn't stop me from predicting exactly what's going to happen, everytime, invariably. Thats my point, and I even said that it doesn't apply to everything. As I said in the original post, I don't know much about ocean trench formation, it doesn't mean that I should immediately assume that it's unpredictable; in fact, it seems like it should be the opposite (and some would agree, as previous posts suggest). Just because some things are unpredictable, as chaos theory suggests, does not mean it's wrong to use invariably in general, not everything is unpredictable!: Isn't a fundamental principle of science repeatability? The same outcomes are necessary.

    Oh, and don't try and be patronising, your not five-years-old and it's extremely doubtful that you're as intelligent as you think. You didn't have to contribute to the thread, others have contributed something constructive, you didn't.
    Last edited: Jul 15, 2010
  11. Jul 15, 2010 #10
    I believe one of the points Jon was making - and one with which I would agree - is that nothing in science is exact.

    From a practical point of view there are errors in the precision with which we define the starting conditions, so the exact outcome cannot ever be know. Beyond that there are, in the chaotic systems mentioned by Jon, situations where very small differences in the starting conditions produce massive differences in the end results. I am sure you are familiar with the butterfly effect.

    Going even further, quantum uncertainty means that we can never know exactly what will happen, because at quantum levels we find we can never specify the starting conditions exactly.

    Of course all of this is off topic from the rather more interesting - in my opinion - subject of oceanic trenches. However, I did think it was worth noting that Jon's observations seem to me to be valid. Whether they are relevant - well, as I said I think we have all drifted off topic rather badly.
  12. Jul 15, 2010 #11
    I don't disagree, I'm not in a position to do so.

    But I think that when I assumed that the outcome of ocean trench formation could be predicted it was not a competely absurd assumption. Somethings, as I've said many times, can be predicted given enough information.

    None of my previous post was directed to you Ophiolite, you have been very helpful, and I'm thankful. I was actually annoyed at his tone and attitude. They didn't contribute anything and were extremely rude, I don't come here to be ridiculed or mocked.

    But I agree, this is off topic slightly!
    Thanks again, Ophiolite.
  13. Jul 15, 2010 #12
    Condescending to Newton is laughable? So condescending to other people is...?
    Tell me, what makes you think one must be condescending to mention that a given branch of study had not been recognised in the days of Newton? Or Laplace? (Oh yes, BTW it was Laplace; I checked!) That is not at all the same as saying how silly those old fogies must have been, not to have thought of such things for themselves!

    Look nobahar, I never patronise anyone unless I am angry enough to be very rude, and not often then. I am not angry now, nor when I was writing my previous note. You are being pointlessly rude, and it does not seem to be making you very cheerful.
    Think of this. When this discussion began I had addressed Ophiolite about a remark that I thought too good to reserve for geology, and you will note that he never saw fit to bite me. It is an example that you could bear in mind whether you follow it or not.
    Now, whether one of us owes the other any more apologies than the other way around, I leave you to think over. When I first read this thread I did not realise that you were a youngster. Sorry about that, but as I remember it, I never noticed where you pointed that out. If I had, I would have been more careful to avoid some words that most of the mature people in forum would have understood without my explaining them.
    Do you think I would I have done that because I thought you were too stupid to understand jargon? Or because I wanted to show you up? Certainly not. For one thing, I think it a good thing for youngsters to join and talk along. And if they learn from it and enjoy, it is not just a good thing, but a great reward all round, both to those that have passed on an idea and those that have been enriched. In fact it can be very difficult to predict which way round that happens.
    But since I did not know, I used the words of hurry and short-cutting. While we are quoting great Frenchmen, Pascal is the earliest source I can find for "I have made this letter longer than usual, because I I lack the time to make it short," though something of the type is attributed to about a dozen other writers. Well, one could write something vaguely analogous about jargon, say: "I have used the usual jargon because I did not realise that it was time to speak English."
    Well, that is why I did so, more or less.
    So, it was all my fault? Possibly, but I have actually spoken to young people before, and made myself understood first time. But those were usually when I knew that I was not speaking to professionals.

    If you know that something "invariably happens", you can use that knowledge as the basis for certain types of proof. Right? See the connection?

    nobahar, atheism is a religion. How it got into this discussion, I don't follow. Don't bother to explain unless you have a real cruncher of an argument to connect it to science on the one hand, and invariable prediction on the other.

    As for evolution, be very, very careful. Certain subjects are very treacherous. They are based on simple facts and principles, so anyone with half a brain can read them and say something like: "Oh I see! That is obvious! Now I understand that subject!" Then they lead you into pitfall after pitfall. Only the experts get to see just how many kinds of pitfall are waiting, and that is because they have been caught out so many times that they no longer are embarrassed when it happens. Elementary probability theory is one such subject. Evolution ("Darwinism" to be more precise) is another. Trust me, you did yourself no favours with your remark about evolution.

    Does it apply to anything? You are missing whole fields of scientific philosophy and other whole fields of scientific practice. I had to catch myself from beginning to name some; I really am rather short of time and you seem to be a bit short on tolerance at the moment. If ever you get interested enough, feel welcome to contact me and ask for a few pointers to useful reading matter. One excellent site to surf would be http://plato.stanford.edu/
    Some marvellous books would be the collected mathematical recreations and essays of the late (deeply) lamented Martin Gardner.

    Hm... some gave you some helpful and informed discussion, but none gave you everything, which is precisely why it is so useful in these threads to have helpful people chipping in to amplify each other's remarks or put them into broader and deeper perspectives. The privilege of being able to call on them so easily is something more valuable than you could easily imagine. I haven't got over it myself.

    Here I rather unusually put my foot down with a clang! NO! It is NOT! (At least two clangs in fact, as you can see!) It is arguable to what extent we can achieve repeatability in any branch of science at any time, and how we would define it if we could. Let me know if this strikes you as hard to imagine. In Earth sciences, Biological sciences and applied sciences in general, this is particularly true, but ultimately it applies to the lot. (Again, here we also run into the problem of abstraction, in which we decide how to strip out the parts that we may "safely" ignore. But we also run into a lot of huge logical and philosophical problems. If those are not to your taste, ignore them... for now ...

    Now, in case I did not make the point clear enough, I am very keen for you to continue reading and asking questions in blogs of this type. It is unusual in young people and suggests that you are intelligent. It is well to develop a good mind by being mentally predatory from as young as possible. For example, your question in this thread was a good one. But cool it. There is not a great deal you can learn while you are having conniptions.

    Go well,

    Last edited: Jul 15, 2010
  14. Jul 15, 2010 #13
    Okay, now that this thread is completely off-topic, I think it should probably end here!
    I am actually going to apologise aswell, I am sorry for the comments that I made earlier, they were said in anger, and I apologise.
  15. Jul 15, 2010 #14
    Handsomely said (NO patronism!!! It really was handsomely said.) And I apologise for annoying you.


    Last edited: Jul 15, 2010
  16. Jul 18, 2010 #15


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    FWIW -




    Ref: http://en.wikipedia.org/wiki/Mindanao#Mountains_and_plateaus



  17. Aug 11, 2011 #16
    As the Ocean trenches happens at the areas where two plates collide .It's possible that this causes one plate to move towards the other and two plates collide. for ex the Peru-Chile ocean trench
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