Tag: science

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Why Convection Rolls of the Mantle Form a Regular Pattern

Steingrimur Thorbjarnarson

Convection rolls within the mantle have an adiabatic heat gradient, starting at the border between tectonic plate bottom and the layer below. Logically, the mantle must therefore as a whole be on the verge of being ductile and stagnant. A tectonic plate is 120 km thick, according to the defination that its lowermost border is where convection, or constant flow of mantle material, is found.

It has been found in laboratories, that if mantle material at this point (convecting but very close to becoming stagnant) does form convection rolls. As reality and experimental results are to be compared, especially if no other factors affecting real circumstances than used during experiment can be pointed out, inserting the outcome of experiment into known and measured circumstances is indeed a piece of work any scientist should undertake.

In this case it is easy, because the thickness of inner layers of Earth are known. Putting togherher the outcome of the experiments in laboratories, the logic of adiabadic thermal gradient, and knowledge about the depth of each layer, this is the outcome:

This is the basic picture of a section of convection rolls within the Earth. Inserting the results of experiments, fits exactly into measured environment.

Most people recognize the core, mantle and crust, and some might notice the Gutenberg layer, also known as the core-mantle boundary or CMB. This is a beginning of a study described in the book found here on this webpage. Reading that book is of course more difficult than reading this short post, and most people do certainly not have time enough to read it. It can be said here, though, that all the implications have been worked out, and how the convection rolls form a 3D system within the Earth is thereby fully understood. In turn, it enhances our overall understanding of geology.

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The Convection Rolls Model – How is it Derived?

Steingrimur Thorbjarnarson

The Convection Rolls Model has been used to explain a myriad of geological features. The starting point is easy to derive, because the layers of Earth have a regular pattern, and Rayleigh-Bénard type of convection rolls fit precisely into it.

Layers of Earth and Rayleigh-Bénard convection rolls inserted.

The convection rolls are affected by the rotation of the Earth, and the same proportions prevail farther north and south within the rotational plane. The height and width of the mantle convection rolls therefore adhere to the physics of Rayleigh-Bénard convection all over the globe.

Therefore, it was possible to derive the comprehensive or global convection rolls model, starting from the obvious match within the equatorial plane.

The match shown above is mathematical, to show that the intersection zones are really intersections between main layers. At equator, the convection rolls tend to be arranged directly above each other.

This drawing shows how the convection rolls are arranged directly above each other. It also shows secondary convection rolls within the lower mantle. The Lehmann layer of the core is omitted here. The system can then be traced northwards and southwards, and the global system derived, which is described here.

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Mantle Convection or Mantle Plumes?

Steingrimur Thorbjarnarson

In Iceland, many people think that a mantle plume is responsible for volcanic activity. The plume is thought to be centered around the western part of Vatnajökull. All the same Gilliam R. Foulger came to the conclusion that a plume, of the kind imaged, can not exist. https://www.mantleplumes.org/WebDocuments/P%5E2Rev_Harangi.pdf

In fact, Foulger does find a proof that this kind of plume does not exist. The relevant data shows that no continuous hot mass is ascending under Iceland. Therefore we should stop imaging this plume and continue the search for the inner structure of Earth with measurements and calculations according to the physical properties of the mantle.

Convection does, on the other hand, fit all available data. Experiments show that mantle material forms convection rolls under those circumstances expected to prevail within the Earth. Testing it, by making a model with convection rolls filling the measured layers, shows remarkable results. Features on Earth, both divergent and convergent, fit to the convection rolls underneath.

Now, when this has been solved, it is very easy to proceed with research programs, further improving our understanding of the inner structure of the Earth. First, we have to admit that the former idea about mantle plumes is wrong. A model of a regular system of convection rolls is what brings us farther ahead. Luckily, we have the scientific method to assist us with our work. By having a foundation of physics, measurements, mapping, calculations and logical thinking, besides being able to communicate freely, these steps forwards can be made.

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Volcanic Activity near Grindavík on the Reykjanes Peninsula

Steingrimur Thorbjarnarson

The volcanic activity near Grindavík can be explained by referring to the interaction between a dyke forming within the volcanic zone, and magma from the dyke finding its way to the surface through earthquake faults. A seismic zone creats a weakness of the crust within the area. The orientation of the dyke is quite different from that of the earthquake faults. According to calculations the dyke is oriented about N43°E, and the earthquake faults trend is directly N-S. Real circumstances are not quite so simple, because the upper most manifestations of earthquake faults are en échelon arranged, divided into smaller systems with NE-SW trend. The dyke, when meeting with the earthquake faults, also bends, or follows the N-S trend near the eruption site. As I have been exploring the possibility that convection rolls are found withn the asthenosphere, and mapping the division lines between them, it is interesting to compare those lines with the conditions at the eruption site. Two downwelling lines of the lower parts of the asthenosphere are found directly below the eruption site itself. To understand the situation better, we should have a look at a map showing this:

This shows how the black division line crosses the Reykjanes Seismic Zone shown with red parallel lines. It is tempting to assume that the origin of magma can be traced to those two division lines directly below the eruption site. Another possibility is that the magma is originated from the upper most division line, alinged NE-SW, found slightly west of the eruption site, flowing at first under the crust along the NW-SE aligned line until it reaches the eruption site area. Then it ascends into magma chambers and finally to the surface.

This site shows many different situations where convection rolls system and real circumstances fit together. This is of course a very good example. The fact that the three eruptions along the dyke which formed under Fagradalsfjall, and the four eruption that have already taken place along the dyke forming at the side of Sundshnúkur have the same petrological origin is consistent with this.

This is an explanation built on many years of research. I have taken part in a series of conferences and meetings, publishing papers where the scientific papers pointing in this direction are cited. I also took part in mapping the South Iceland Seismic Zone, giving me the feeling of how the seismic area of Reykjanes works, as those two systems are connected end-to-end.

To explain the heat flow within the Earth, from radioactivity to eruption, is not easy, but it can be done. This eruption deserves much attention, and among the countless examples shown here, this one of those literally to the point.

The two other seismic zones of West Iceland (BTZ) and South Iceland (SISZ) are added to show how likely it is that the polygons surrounding distinct areas of Iceland really exist. To form a seismic area, pressure is nedded. The faults are all N-S oriented, so regularity is needed. The parallel faults are found side by side in E-W direction, having distinct endpoints, so the area is limited. The only solution for an outer framework is a polygon, exactly as drawn on the map here above. The division lines between convection rolls coincide with this enevitable polygonal shape surrounding the seismic zones. Therefore, it makes sense that the division lines are responsible for shaping the polygons in the first place. It is all about logic.