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Rockaholic Adventures

Rockaholic Adventures is the place for conversation and discussion about outdoor excursions. You'll also read reviews written from the perspective of today's technologically-advanced outdoorsman - one with a background in engineering and geology. Here, you'll find everything from discussions about geology-related engineering disasters to insights about how advances in technology have transformed modern-day extreme sports.

Rockaholic Adventures also covers topics such as urban planning and other anthro-induced changes to the access and preservation of natural areas. The blog's owner, Shawn, holds an A.S. from Hudson Valley Community College (HVCC) with a concentration in science and engineering, and a B.S. from the State University of New York (SUNY) at Albany with a major in geology.

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Hot-Spots and Tectonic Plate Directional Vectors

Posted July 17, 2008 5:00 AM by Shawn

Do areas of persistent volcanic activity that burn through the lithosphere, the part of Earth's outer layer that contains the crust and the upper part of the mantle, remain in a fixed location as to act as a reference point? Can we use remnants of persistent volcanic activity in the ocean floor to track tectonic plate motion?

Areas like the Hawaiian Islands and large calderas as thought to exist in Yellowstone Park in Wyoming are fed by hot-spots. In common terms hot spots are more or less exactly what the name implies. They are isolated areas of increased heat flow that convect magma from deep within our earth and persist over geological time spans.

Hot-spots are theorized to originate in the upper mantle or as deep as the core-mantle boundary where the D" Layer, a theoretical thin layer of the earth separating the liquid outer core from the solid inner mantle and accompanied by a defiant change in seismic waves and crystal structure of existing rock mass, exists. They do not streamline right to the surface, but rather feed large plumes of hot magma that flow through cracks and find the path of least resistance as the attempt to surface.

They can either cause extrusive or intrusive igneous bodies to form. Extrusive, meaning they surface through volcanic activity or intrusive meaning they do not surface, but rather cool and solidify within the crustal segment of the lithosphere.

As you may recall from reading "China's Earthquake and the Indus-Yarlung Suture Zone", plate tectonic theory divides Earth's crust into thin, rigid segments that move horizontally and adjoin other plates. Hot-spots are thought to remain in a fixed location as tectonic plates float and pass over the plume of hot magma that is fed by these laminar-like flow patterns.

The Hawaiian Islands may be the best example of how a hot spot that feeds island volcanoes has seemingly remained in a fixed location for at least 40 to 80 million years. The erupting magmas have formed what is presently referred to as the Hawaiian-Emperor seamount chain. There is an obvious change in the Pacific Plate motion around 50 to 40 MYA. Other than the sharp bend observed during this time frame, the plate seems to move uniformly. Is this abnormal and can we rely on the superposition of these laminar-like flow patterns to dispel plate motion?

Resources:

http://www.platetectonics.com/book/page_17.asp

http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

http://en.wikipedia.org/wiki/Hotspot_(geology)

http://www.wwnorton.com/college/geo/egeo2/content/animations/2_6.htm

http://www.gps.caltech.edu/~gurnis/Movies/Animated_GIFs/Pyre_global-plume.gif

http://www.cems.umn.edu/research/wentzcovitch/highlights/science_now_040324.htm

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#1

Re: Hot-Spots and Tectonic Plate Directional Vectors

07/18/2008 12:50 PM

Something I have casually wondered about ever since I first heard of these hot spots. Are they more or less permanently located? They seem to remain for tens of millions of years at least, which, if not permanent, is almighty persistent!

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#2
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/18/2008 1:53 PM

In studying plate motion I have seen hot spots used as reference points. I never quite believed that a isolated convection cycle in such a dynamic environment could bypass the external forces that might act on it.

When viewing diagrams with plate velocity vectors, I believe we see Africa nearly stationary while ocean ridges exist on opposing borders. If Mid-Ocean ridges are not stationary can we prove that the exact location of some hot spots are indeed in motion as well?

Personally, I think Hawaii is a special case.

http://commons.wikimedia.org/wiki/Image:Tectonic_plates_boundaries_detailed-fr.svg

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#3
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/18/2008 3:00 PM

It's special for sure, there's something non-standard going on! I concur that the environs are far more dynamic than I would expect something like a convection cycle to stand mostly still in either. Seems to me it would be equal to a whirlpool standing still going over Niagra Falls.

Still, those velocity vectors may be somewhat misrepresented. Something has to be used as a reference point, but it may be illusory to think of any part of the surface to be absolutely stationary (or anything like stationary) in the long run.

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#4
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/18/2008 3:29 PM

When they build those models I believe they use the rotational inertia about earth axis of rotation and possibly a second seemingly fixed point. Most computer models and journal articles I have read support the idea that Africa is seemingly fixed and more so the volcanic activity observed in Hawaii. I believe the model is pretty close. I just don't know of any true point of reference and have my doubts any other hot spots behave as well as the Hawaiian example.

http://www.sciencemag.org/cgi/content/abstract/175/4028/1355?ck=nck

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#5
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/18/2008 4:01 PM

Well, there's nothing I would usually like better than a rowdy hot spot...

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#6

Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 5:43 AM

Hi,

why shall the Hot-Spots be stationary?

official theory says so but without any arguments.

In contrary I am convinced that Hot-Spots are not stationary:

rising plumes in a viscous fluid are like tobacco smoke from the tip of a cigarette that is rising in air (no wind-speed). May be the viscosity is much higher so we should calculate the Reynolds number to estimate onset of first vortices.

If Re is below 1 so that there are no vortices at all then there are the electromagnetic forces from a moving conductor in a magnetic field.

This not enough there are Coriolis forces at rising material as the velocity near the center of earth is lower than near the surface. This causing a westward deviation.

We have no inertial frame to detect the motion so we cannot distinguish plate motion from hot-spot motion.

What would interest me: how much material is rising at which velocity in a hot spot?

How much of this will come to surface as a volcanic eruption?

I am living not too far from a hot spot that can be traced for the last 1.5x109years, starting the Eifel-volcanoes in Germany beginning 25 million years ago and the last eruption 10,000years ago ( a really big one) and a ready to move upwards magma-chamber waiting for the next eruption.

Not very likely that we will see it but if: then dramatic.

RHABE

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#7
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 7:07 AM

Our Yellowstone seems similar. It's said to be a potential volcano of enormous proportion waiting to erupt. Personally, I don't need such drama, but I suppose there's not a whole lot of choice involved...

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#8
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 8:22 AM

I agree that the fixed location of a hot spot seems most likely, yet the Hawaii-Emperor Seamount Chain accurately describes the plate motion of the Pacific plate for the last 80 million years. The sharp bend around 40-50MYA correlates with the separation of Australia-New Guinea from Antarctica as well as the collision of the Indian plate with the Eurasian Plate.

80 MYA may not be a long time for a convection cycle within Earth's crust, yet they hot-spot feeding the Hawaiian Islands seems to have had been fed by a critically hot mass that continues to rise with heat and velocity that remains unscathed by any external forces.

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#9
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 8:59 AM

I know the observational evidence for at least some hot spots remaining more or less stationary, but as RHABE mentioned, there has to be some sort of justification for this being so. We can't just postulate that it seems so, therefore it is so. There has to be a description of the likely mechanism, or it's just another case of "at this point, a miracle occurs". What good is that?

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#10
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 9:21 AM

Its obviously a deep epicenter convection cycle. Most likely originating far beneath the massive convection cycles that feed the mid ocean ridges. The beauty is that there is no direct observation as to what feeds these anomalies.

We know they exist and feed plumes of hot magma that melt away a shallow pool in the lithosphere. The fact that they remain stationary argumentively disproves that basal drag is a major driving force in plate tectonics.

Possibly, extremely thick oceanic plates that become subducted are unable to heat uniformly and some mass sinks below existing convection cycles. This mass could displace or eventually heat up and escape the D" layer? Rising at great velocity so that it eats through the slow moving outer mantle like a hot knife through butter.

The turbulence could streamline the flow until the hot-spot weakens as we have not yet seen in Hawaii where we would expect it to lose stability, wonder and posisbly die-off. Who knows how long that could take?

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#11
In reply to #10

Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 9:37 AM

Obviously it takes at least several tens of millions of years.

"...Rising at great velocity..."

Great being a relative term, of course. But sure, why not huge chunks of more-or-less consolidated plate material. It could act as a flow diverter or constricter. But would this maintain its function over that long a time?

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#12
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 9:46 AM

Oceanic crust on average is surfaced for about 200 Million years. Beyond this time span you may consider it to be abnormally thick, and since oceanic crust is destined to be consumed by the convection cycle after subduction I would expect such a cycle to exist for at least 200 million years.

I wouldn't offer a theorem if I didn't believe it held some water. I would also expect most people to be highly subjective in believing such a statement, and I open the floor to anyone that has a better theory as to why these anomalies exist and what force could possibly feed them. Are they related to magnetic reversals?

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#14
In reply to #12

Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 10:52 AM

"Are they related to magnetic reversals?"

Hadn't thought of that, and if I ever get free time to research the potential timelines, I'll try to form an educated opinion.

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#15
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Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 1:02 PM

I can't take the sole credit for my suggestions. It is an area in Geology that there has been a lot of throwing our hands in the air due to limiting data sets or inability to measure.

The following paper suggests that there are multiple mechanism that can induce hot-spots. Please remember that plate tectonics is a developing science and that many specifics are still left as a fronteir.

http://www.sciencemag.org/cgi/content/summary/300/5621/920

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#13
In reply to #7

Re: Hot-Spots and Tectonic Plate Directional Vectors

07/22/2008 10:07 AM

Yellowstone is similar in action but much bigger in size.

From the last eruption of "Laacher See volcano" there remains only a small (1km diameter) Maar = craterlake where a famous medieval monastery is situated.

Nearby (30km) Rhine-valley has covers of lapilli only 25m thick.

RHABE

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