Types of Mountains

Discussion in 'Earth Science' started by kingwinner, Oct 1, 2005.

  1. valich Registered Senior Member

    Yes, but what I do not know - totally because of my ignorance of the New Zealand geographic region - is, is this considered a mountain? Or is it a geological land mass build up? Where erosion has just filled in the low-lying areas? New Zealand is a fascinating geological and biodiverse region that I can only hope to someday explore in my lifetime.
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  3. Laika Space Bitch Registered Senior Member

    I have a couple of small nit-picks with what you've said here Valich:

    While some mountains certainly are constructed from gradually accumulating deposits of volcanic rock (the Hawaiian Islands providing a prime example), I don't think you're justified in saying that this is the origin of most mountains.

    I'm not sure if you meant magmatic instead of volcanic. If you did, I'd take issue with that too. I will present the Alps as a lovely example of a mountain range formed by tectonic convergence. This range was formed not by magmatic processes, but by the accommodation of crustal shortening via folding and thrust stacking. There are igneous rocks exposed in some areas, though in my ignorance I don't know whether they were intruded during orogenesis or if they simply represent basement rock involved in the deformation. Either way, the Alps consist largely of sedimentary and metasedimentary rock-types, and I believe a similar thing can be said of the Himalayas.

    About the Andes I know practically nothing, but I imagine that magmatism and volcanism has played a larger role in their formation. Even so, I expect that thrusting and folding will still have provided the main cause for crustal thickening.

    You also say:

    One key point about mountains is that erosion begins as soon as they rise above the depositional level, so while unconsolidated sediment may accumulate locally, in general it will be rapidly stripped away. Beautiful folds can most certainly be very visually apparent.
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  5. valich Registered Senior Member

    Dear Nit Bitch: I have no time for senseless nitpicking. In any case, the Hawaii islands are formed from volcanic rifts in mid-ocean tectonic plate ridges that resulted in the accumulation of magma being built up and the result are the active and inactive volcanoes that make up the Hawaiin Islands today. Read my above posts specifically regarding the Hawaiin Island volcanoe system above. Thanks.

    I have never made any mention of the Alps. You are certainly welcome to share with us your intelligent explanations and views. Please do. Thank you.

    Magma consolidates within the crust to form igneous rock. Magma that extrudes onto the Eath's surface is then called lava. There's really not much of a big difference to worth arguing about. Both magma and lava have various compositional components of mineral makeup.

    Your last point is a bit obscure. Certainly erosion begins as soon as Nature's forces act on the deposition. What do you consider as a "depositional level"? Of course igneous rock will not erode as fast as sedimentary rock, and sedimentary rock may take hold as plant life starts to grow. This then adds to further sedimentary deposits. I don't see the point of what you're trying to say. Yes, of course, erosion is always a factor in our environment? And?
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  7. Laika Space Bitch Registered Senior Member

    I'm sorry if you think that what I wrote was senseless, but you said a few things that I thought were erroneous. Now there's one more:

    The Hawaiian Islands do not lie on a mid-ocean ridge, but sit atop a hot spot. Plate tectonics has carried the plate over this relatively static point, causing a mountain chain which youngs to the south east.

    The reason I differentiated between magma and lava is that you claimed that:

    Granted, the Hawaiian chain has been formed through such processes (though in an intraplate setting). But I still do not think your claim is justified. Some mountains, surely... but most?

    I brought up the Alps because it is a range about which I am not wholly ignorant, and because I believe they provide an example of a range in which magmatic and volcanic processes are largely irrelevant.

    I brought up erosion because of your claim that:

    Erosion will ensure that the "thin surface of sedimentary deposits" will be a fleeting feature of a mountain.
  8. valich Registered Senior Member

    Well, I certainly never claimed that "the thin surface of sedimenary deposits is a "fleeting feature of a mountain"". But the Hawaiin Islands are a serious of volcanoes.

    "The Hawaiian Islands do not lie on a mid-ocean ridge, but sit atop a hot spot. Plate tectonics has carried the plate over this relatively static point, causing a mountain chain which youngs to the south east."

    This is absolutely correct, but, as I said, it is due to plate tectonic activity. I don't believe that I said convergence, subduction, or abduction. Nevertheless, without a rift, how can you account for magma immerging outward to form volcanic uplift?

    "A hot spot is a stationary activity relative to the moving tectonic plate above it, so a chain of islands results as the plate drifts. Over long periods of time, this type of island is eventually eroded down and "drowned" by isostatic adjustment, becoming a seamount. Plate movement across a hot-spot produces a line of islands oriented in the direction of the plate movement. An example is the Hawaiian Islands"

    Without sometype of a rift or a crack between the tectonic plates, how can you account for magma uplift that now produces the active lava-flowing volcanic islands of Hawaii today? I have no other explanation. Do you?

    The Aplines or Alpides consist of both the Alps in Europe and the Himalayas in Asia. This is because their mutually folding both began together during the Tertiary (1.7 mya).
  9. invert_nexus Ze do caixao Valued Senior Member

    Oh Christ.
    I don't have time to lambast you as you deserve, but just give it up, Valich.
    You very clearly stated that " the Hawaii islands are formed from volcanic rifts in mid-ocean tectonic plate ridges". It doesn't matter if you mentioned "convergence, subduction, or abduction" in regards to said activity. You very clearly stated 'tectonic plate ridges'.

    So. Just give it up and admit that you said a stupid thing. This is why people hate you, you know.

    And yes. Hawaii has formed as a series of islands because of plate tectonics, but the hot spot itself has nothing to do with tectonics.

    You're such a fucking dick. I shit you not.
  10. valich Registered Senior Member

    Regarding the Hawaiin Island volcanoes, I think that what is most confusing is: "What differentiates "hot spots" from cracks or ridges in a plate?" There seems to be a few other Sciforums that are now addressing this issue ("Earth Science" category). Basically, though, hot spots are similar to cracks in tectonic plates, but these socalled "hot spots" occur within, rather than on the edges of lithospheric tectonic plates. I think that this is where the confusion lies: hot magma rises from movement of tectonic plates to create volcanic activity.

    "Hawaii is a classic example of a "hot-spot trail", created by a giant plume of magma that rises from the core of the Earth to the surface. As the Pacific plate passes over the plume....Such mantle plumes are deeply entrenched in the geological "standard model", going hand-in-hand with plate tectonics."

    "Geologists believe that a huge column of upwelling lava, known as a “plume,” lies at a fixed position under the Pacific Plate. As the ocean floor moves over this “hot spot” at about five inches a year, the upwelling lava creates a steady succession of new volcanoes that migrate along with the plate - a conveyor belt of volcanic islands"

    In general: "The magma rises through the Pacific Plate to supply the active volcanoes."

    The United State Geological Service (USGS) refers to this area as a "ridge":
    "Over the past 70 million years, the combined processes of magma formation, volcano eruption and growth, and continued movement of the Pacific Plate over the stationary Hawaiian "hot-spot" have left a long trail of volcanoes across the Pacific Ocean floor. The Hawaiian Ridge-Emperor Seamounts chain extends some 6,000 km from the "Big Island" of Hawaii to the Aleutian Trench off Alaska. The Hawaiian Islands themselves are a very small part of the chain and are the youngest islands in the immense, mostly submarine mountain chain composed of more than 80 volcanoes. The length of the Hawaiian Ridge segment alone, from the Big Island northwest to Midway Island, is about equal to the distance from Washington, D.C. to Denver, Colorado (2,600 km)...A sharp bend in the chain indicates that the motion of the Pacific Plate abruptly changed about 43 million years ago, as it took a more westerly turn from its earlier northerly direction. Why the Pacific Plate changed direction is not known, but the change may be related in some way to the collision of India into the Asian continent, which began about the same time. As the Pacific Plate continues to move west-northwest, the Island of Hawaii will be carried beyond the hotspot by plate motion."

    "The prevailing theory among geophysicists is that the Hawaii-Emperor Seamounts formed as the Pacific Plate moved over a fixed hot spot that today is located beneath the island of Hawaii and is responsible for the world's most active volcano, Kilauea. The segment known as the Hawaiian Ridge, which includes the main Hawaiian Islands and a chain of islands, atolls, and seamounts known collectively as the Northwestern Hawaiian Islands, extends some 1,800 miles (3,000 kilometers) northwest across the Pacific. At the end of the Northwestern Hawaiian Islands, the chain turns sharply northward and becomes the Emperor Seamoun. According to most researchers, this sharp bend represents a rapid change in direction of the Pacific Plate as it passed over the fixed hot spot 47 million years ago."

    "Hot spot volcanoes often have long rift zones that radiate from a summit caldera, along which smaller vents and fissures occur. HAWAII, MAUI, NI'IHAU - High-resolution bathymetric maps show that submarine flat-topped volcanic cones are common on the submarine rift zones of Kilauea, Kohala, Mahukona, and Haleakala volcanoes. Samples show these cones are tholeiitic basalt erupted during the shield-building stage. These flat-topped cones appear to have formed during effusive eruptions lasting years to decades, and apparently form as continuously overflowing submarine lava ponds.

    "Two forms of Hawaiian volcanism are poorly understood: post-erosional eruptions and the Hawaiian Arch flows. Various hypotheses have been forwarded to explain these magmatic events; one such mechanism that is relatively undeveloped associates volcanism with the topographic uplift caused by lithospheric flexure. We propose a model in which melt is generated as a direct consequence of the flexural uplift, which surrounds new volcanic shields as they grow. This uplift causes upward flow and decompression of the underlying asthenosphere. We assume that a thick (100 km), heterogeneous layer of asthenosphere is near its solidus, a condition resulting from mantle plume material that first melted partially beneath the shield, but has since flowed laterally away from the shield. One prediction of our model is similar geochemical characteristics between the two types of volcanism, and this is consistent with results of recent geochemical studies. Another prediction is volcanism occurs where the lithosphere is actively rising, during the loading of a volcanic shield."

    "The concept of a hot spot envisions a small source of heat fixed deep in the Earth, below the lithospheric plates. Molten rock from the heat source rises rapidly, melting its way through the overlying lithospheric plate and emerging on the surface to form a volcano. But because the plate is moving, the volcano is soon carried away from the point over the heat source, and becomes dormant. The hot spot burns its way through the lithosphere directly above it and begins to construct a new volcano. The result is an ever-lengthening line of volcanoes whose abrupt beginning at an active vent marks the location of the hot spot itself."

    "Mantle Hot Spots: where magma burns a hole through the crust in the middle of a tectonic plate. While this type of volcano may occur in the middle of continental crust, the best and most abundant examples of hot spots are to be found in the middle of oceanic plates. Because this magma is not “recently” recycled crustal material, it tends to be lower in SiO2 content, producing the quiet type of volcanic eruption that is characterized by gentle lava flows of black basalt."

    "A major puzzle for proponents of the theory of plate tectonics, and a key complaint of those who resisted this theory, was the formation of island chains like the Hawaiian Islands. How could a trail of islands form in the middle of a plate away from its boundaries if the centers of volcanic activity were oceanic ridges?

    The answer was provided by a famous Canadian geologist, J. Tuzo Wilson, who hypothesized in 1963 that the plates did indeed move, but that certain regions of the crust are characterized by "hot spots." These hot spots represent regions where magma continuously breaks through the lithosphere, i.e. they represent stationary magma sources in the asthenosphere. As the plates move across these hot spots, volcanic islands are formed"

    Also see: http://www.emporia.edu/earthsci/student/sedlacek2/mantle.htm
  11. valich Registered Senior Member

    GET A LIFE!!!
  12. valich Registered Senior Member

    I think that this is the key:

    "The concept of a hot spot envisions a small source of heat fixed deep in the Earth, below the lithospheric plates. Molten rock from the heat source rises rapidly, melting its way through the overlying lithospheric plate and emerging on the surface to form a volcano."

    The lithospere is about 60 miles thick, while a tectonic plate is only a small segment of that area of the lithosphere. So where plate teconic explanations stop - although how can they totaly stop: they have to provide an opening? - the underlying magma uplifting the lithosphere explains that origin source.
  13. Xylene Valued Senior Member

    The Northland region is mostly plain, fairly low-set by New Zealand standards, i.e. below 600 ft a.s.l. The trench into which the sediment fell was quite deep, several thousand feet, so there's a long sedimentary column. The scene is complicated by comparitively recent volcanism, which occurred between about 20 million (west coast) and 3 millon years ago (east coast). Apart from that volcanic activity, everything else is sedimentary. It's a mountain in reverse, if you like--an upside down mountain range.
  14. invert_nexus Ze do caixao Valued Senior Member

    Get some integrity.
  15. valich Registered Senior Member

    Wow! Complicated indeed, but thanks a lot for the clarification! Now I know exactly what you mean when you were referring to a reverse layering. And your more thorough explanation now deeply motivates me to look into this fascinating scenario of simultaneous trench-filling and volcanic activity in the Northland region. Thanks!
  16. valich Registered Senior Member

    The Wikipedia gives an explanation of the stages of the volcanic buildups in the Hawaiian fissure or ridge, but there seems to be a debate that has been going on now for about thirty years as to whether this socalled "hot spot" is due to thermal convection currents and circulation within the mantle below the lithosphere, or whether it is due to a direct upwelling of a mantle plume originating at the mantle-core boundary. To make matters even worse, to arrive at a more accurate explanation, nowadays the word "hotspot" and "mantle plume" are being used interchangeably. In any case, this hotspot is quite large and remains stationary below the lithosphere while the Pacific plate and the above volcanoes move west northwest above it.

    "The assembly line that forms the volcanoes is driven by a "hot spot," or plume of hot material, deep within the Earth that partially melts to produce magma as it rises beneath the Pacific Plate. As the plate moves west-northwest, each volcano moves with it from its place of origin above the hot spot. The age and orientation of the volcanic chain records the direction and rate of movement of the Pacific Plate. The pronounced 43-million-year-old bend between the Hawaiian Ridge and the Emperor Seamount Chain marks a dramatic change in plate direction."

    Among other factors, it is this pronounced bend leading to two seperate fissure zones that is the most challenging aspect to finding a precise and accurate working hypothesis for the formation of the volcanoes of Hawaii:

    "The Hawaiian chain apparently consists of two strands of volcanoes located along distinct but parallel curving pathways. Multiple volcanoes line up to form each strand....The alignment of the Hawaiian Islands reflected localized volcanic activity along segments of a major fissure zone on the ocean floor. This “great fissure” origin for the islands served as a working hypothesis for subsequent studies until the mid-20th century....Then it was pointed out that the time-progressive volcanism along the Hawaiian chain could be explained by the lithosphere moving across a stationary hot spot in the mantle. This led to the theory of deep mantle plumes when Morgan [1971; 1972] proposed that a) this hot spot was continually supplied by a plume from the deep mantle, and b) there are approximately 20 such plumes in the mantle. Fixity relative to one-another, time-progressive volcanic tracks, and a high rate of volcanism were considered to be the primary characteristics of volcanic regions fuelled by deep-mantle plumes.

    The Hawaiian - Emperor system appears superficially to fit the fixed deep mantle plume hypothesis well....The most compelling and widely quoted evidence today is still geometric considerations such as fixity, perceived parallelism with other volcanic chains and the regular time progression of volcanism, along with the high melt productivity. Lnear time-progression of volcanism and high magmatic productivity can be explained by other mechanisms such as propagating cracks and high mantle fertility. Nevertheless, for about 20 years there has been no serious challenge to the fluid-dynamic, deep thermal mantle plume hypothesis for the origin of the Emperor and Hawaiian islands and seamounts. There are, however, a substantial number of aspects of the chains that are not predicted by the plume hypothesis and fit it poorly. These must give clues to alternative genesis models.....

    Aspects of the Emperor and Hawaiian chains unpredicted by the plume hypothesis:
    1) The “bend” did not result from a change in direction of Pacific plate motion....In addition to the change in trend, the locus of volcanism moved south by ~ 800 km relative to the geomagnetic and biofacies reference frames while the Emperor Seamount chain formed.
    2) The Emperor chain began near a ridge.
    3) There is no Emperor/Hawaiian “plume head."
    4) The magmatic rate is highly variable.
    5) There is no heatflow anomaly: Lithosphere underlain by a thermal plume is expected to be thinner and to have higher heat flow than the average for lithosphere of the same age elsewhere. Heatflow across the Hawaiian swell, however, shows no significant anomaly.
    6) Mantle temperature is elevated by up to ~ 200°C: Petrology can be used to infer the temperature where surface-erupted melts were last in equilibrium with the mantle source, and Tp, the mantle potential temperature. The results for Hawaii are variable, and whether or not a high temperature anomaly is inferred depends on what “average” mantle temperature is considered to be. “Average” mantle temperature is mostly studied at mid-ocean ridges (MORs), since this is where magma of mantle origin is mostly erupted. The temperatures required for plumes to rise are debated. Peridotic plumes from the core-mantle boundary would require temperature anomalies of the order of 600 K.... [However] Combinations of geophysical and geochemical arguments (e.g., “garnet signature” in rare-Earth elements, olivine-liquid geothermometers have been used to infer temperatures beneath Hawaii of [only] 150 - 200 K higher than MORs.
    7) The melt originates from the shallow asthenosphere [upper ~200km region of the 2,900 km mantle].
    8) The basalt geochemistry [of the Hawaiian volcanoes] does not require a mantle plume, or a deep or hot source.
    9) Seismology has not detected a plume.

    Any satisfactory theory for Hawaiian volcanism must explain (or rationalize) the:
    - change in migration direction of the melting locus at the bend,
    association of the great bend with the Mendocino fracture zone,
    - change in migration rate at the bend,
    - apparent commencement of the volcanic chain near a ridge,
    - absence of a “plume head”,
    - large variations in magmatic production, and a current magmatic rate about 3 times greater than the next most productive hotspots,
    - absence of a significant heat flow anomaly,
    - absence of lithospheric thinning,
    - absence of a strong high-temperature signal in the erupted basalts,
    - production of very large volumes of magma even though the depth to the top of the melting column is exceptionally large compared with MORs,
    - spatial and temporal variation in the composition of erupted lavas on a variety of scales, remote location of Hawaii, near the center of a very large plate,
    - seismic whole-mantle mantle structure that is apparently normal compared with the Pacific ocean elsewhere,
    - occurrence of a bathymetric swell (a moat and “arch”) along the eastern two-thirds of the Hawaiian chain and wrapping around its southeastern end, with alkalic basaltic volcanism occurring at some places along it."

    "The Emperor and Hawaiian Volcanic Chains: How well do they fit the plume hypothesis?," by G. R. Foulger1 & Don L. Anderson.
  17. Laika Space Bitch Registered Senior Member

    Indeed, this is what I said. You said:

    And it is that claim which I disagree with.

    Also, remember that this is the Earth Science section of a scientific forum. In this context certain terms carry specific meanings, which may not correspond to their usage in common parlance. You have to be careful, therefore, that when you say "volcanic rifts in mid-ocean tectonic plate ridges", that's really what you mean.

    Anyway, this thread's gone quite far off the topic. The main issue I had with what you posted was that you claimed

    which I think is just plain inaccurate.
  18. Ophiolite Valued Senior Member

    Indeed Laika, as with many (and it may be most) of what Vallich posts he is wholly, totally, irrevocably, absolutely, incontrovertibly incorrect. He has raised flawed thinking to an artform and he must surely be its supreme master.

    [I can actually 'prove' Vallich's statement is correct, but it does require taking some liberties with facts, and some fluid use of definitions. That's what makes his posts dangerous to those trying to learn: he gives the appearance of authenticity, yet supplies severe distortions. A Government Health Warning may be appropriate for all his posts.]
  19. valich Registered Senior Member

    What the hell's your mental problem? Your posts just distract from the educational content of these forums. You profess to be the expert here - challengingly stating: "you're in my area now" - yet you're only posting another condescending obnoxious belittling reply. What's the purpose: simpleminded kicks and jollies?

    From what I learned through my geology curriculum of courses, including one on "plate tectonics," hot spots are not the same as magma plumes. Today, however, most articles seem to use the two terms interchangeably.

    What I was taught - and at the time it was still speculation - and what I continuosly keep learning today, and for the rest of my life for that matter, are the most recent facts. I was taught that there are basically three hypotheses:

    1) That hot spots are created by a plume of magma that rises directly from the mantle/core boundary of the Earth to the lithosphere, or to above it.
    2) That hot spots are due to thermal convection currents and circulation within the mantle below the lithosphere originating from the mantle/core boundary.
    3) Or, that there are two - or possibly more - levels of circulation of magma and solid rock slowly taking place within the mantle: one being within the upper asthenosphere, the others being below it.

    I have not read of any seismographic evidence that proves that any one of the above three are now theories or not. If you know of any more updated information, then please post it. Thanks.
  20. valich Registered Senior Member

    Unfortunately the posts within posts don't post. I don't know how to do that but it doesn't matter, right? Anyways, so what is your counter-theory of the way that the majority of mountains on Earth have formed?

    Also, in reference to a "volcanic rifts in mid-ocean tectonic plate ridges," that is what they are saying that adds to the still unexplained theory and dilemma behind the formation of the Hawaiian volcanoes: that one fissure formed next to a ridge? From what I have been reading, this is one reason why the debate has been going on for thirty years now. The other reasons: refer to what I quoted from citations posted above.

    Please reply. I am eager to learn more and would accept your views as contributing to the world base of knowledge. We all learn and in this way arrive at the facts, or it may lead to more questions, but in any case it leads to progress in scientific knowledge.
  21. Ophiolite Valued Senior Member

    Vallich your post on hot spots is a complete strawman. I am objecting, as Laika did, to your statement that most mountains are formed through volcanic or molten lava activities. This is incorrect. I am belittling you and your posts because they are consistently misleading. I object to you misleading others with your own misunderstanding. Such unscientific behavour deserves to be put down at every opportunity. I shall continue to do so. The only mental problem on display here is your own overtly sociopathic behaviour.
  22. Laika Space Bitch Registered Senior Member

    Well it's not really a counter-theory, but it is quite clear that continental mountain ranges are formed by crustal shortening. This horizontal contraction is accommodated by vertical thickening. The thickening is accomplished by folding and reverse faulting. Although igneous activity (I think generally intrusions of felsic magma) may occur during this process, they are not responsible for the orogeny, but are merely a consequence of it.

    As I say, this is not controversial and, having done no original research of my own, I'm afraid that I'm not "contributing to the world base of knowledge". I wish I could.
    Last edited: Oct 29, 2005
  23. valich Registered Senior Member

    Continental mountain ranges, like the Rockies, Appalachians and Alpine-Himalayas, that we covered above, were formed by subduction, abduction, or convergence of plates. The convergence of two plates, as in the case of the Northern Rockies, leads to buckling up and folding. The Cascade Range is much more complex and involves a circulatory uplifting and deformation of the crust, but is ultimately caused from the San Juan Tectonic Plate moving east underneath the North American Plate.

    Yesterday we posted two replies to a new thread called "Volcano Experts:

    The Eurasian-Melanesian mountain belt is one of two of the Earth's major mountain building systems. The other major active belt is the Circum-Pacific belt system. The Eurasian-Melanesian mountain belt system, sometimes called the Alpino-Mediterranean belt, stretches from Western Europe to New Zealand and includes the Alpine-Himalayan Mountains that were both caused - and are still forming - by the collision and subduction of the African plate and the Indian Plate moving under the European Plate. The Circum-Pacific belt system circles the Pacific Ocean and includes the socalled "pacific Ring of Fire" (producing countless eathquakes and volcanoes) and the Pacific Plate. The subduction of the Pacific Plate under the Asia has produced the mountains in Japan, China, and Borneo. These two huge belt systems pretty much cover all the major mountain ranges in the world. I think the only other major mountain range is the one under the mid-Atlantic Ocean produced by the Mid-Atlantic Ridge, where two plates are diverging and spreading apart.

    You are right though: "mountain ranges are formed by crustal shortening. This horizontal contraction is accommodated by vertical thickening. The thickening is accomplished by folding and reverse faulting." The outermost layer of the Earth is the crust - part of the lithosphere - but underneath this thin chemical crust are the underlying tectonic plates that produce these crustal shortings and vertical tickenings through uplifts, buckling, and folding: the outermost crust is normally only a few miles thick, but the underlying plates can be 50 miles thick.

    About 1/4 of the Earth consists of mountains, but in general, mountains are over 2,000 ft. tall, or else they would be hills.

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