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The Transitional Volcanic Activity of North Iceland

Steingrimur Thorbjarnarson

North and South Iceland seem to be quite different, as there are many volcanic zones active in the south, but only one in the north. The North Volcanic Zone (NVZ) in the north-eastern part of the country replaced the volcanic zone in Húnaflói, extending from Snæfellsnes Peninsula. But volcanic activity has been found in between these two zones in the past, mainly 1-2 million years ago. The Skagafjörður Volcanic Belt was a rift zone, widening the fjord by about 10 kilometers until activity came to an end. Also, activity did occur north of Eyjafjörður, and created for instance Grímsey, where the rocks are known to be around 1 million years old. https://www.visindavefur.is/svar.php?id=4435

This map shows how the transition has taken place in steps of 1.5° from west to east. The map base is from Wikipedia, the lines represent the pattern of division lines resulting from convection within the mantle.

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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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V-shaped ridges, Surtsey, Fagradalsfjall and Ljósufjöll

Steingrimur Thorbjarnarson

The eruptions of Surtsey and Fagradalsfjall can be compared with the recent seismic activity of Ljósufjöll volcanic system at the roots of the Snæfellsnes Peninsula. The V-shaped ridges found on the Reykjanes Ridge also fit into that comparison.

All this activity is found to take place during a little more than half a century. Considering the central location of the Reykjanes Ridge, and the seismic zone associated with both the Reykjanes Oblique Belt and the Borgarfjordur West Lowlands Seismic Zone, it seems more and more logical that these areas can be compared in many ways. Here is another post:

.https://magicmagma.com/2022/09/17/similarities-between-fagradalsfjall-eruptions-2021-2022-and-surtsey-eruptions-1963-1967/

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Similarities between volcanic activity of Reykjanes and Snæfellsnes in Iceland

Steingrimur Thorbjarnarson

New seismic activity has been noticed at Snæfellsnes in Iceland. It can be compared with the present activity at Reykjanes where 10 eruptions have occurred since 2021.

The two volcanic sites, marked on the map, can be compared with the model of convection rolls related to the formation of the Reykjanes Ridge and Kolbeinsey Ridge. Together, they form the sections of the large Mid-Atlantic Ridge found south and north of Iceland. Within Iceland, several volcanic zones replace the mid-ocean ridge, and sometimes Iceland is described as a plateu on the top of the Mid-Atlantic Ridge. The largest volcanic zones, called the West Volcanic Zone, East Volcanic Zone and North Volcanic Zone, are not marked on the map.

Combining the ends of the said two ridge sections, it can be seen that the two volcanic sites have a similar position compared with the relevant line. The site of Snæfellsnes has not erupted yet, but it is known that magma intrusion is responsible for seismic activity there. The Icelandic Met Office has some information regarding the activity at the Snæfellsnes Peninsula:

.https://www.vedur.is/um-vi/frettir/jardskjalftavirkni-vid-grjotarvatn-aukist-undanfarna-manudi?fbclid=IwY2xjawH-bMdleHRuA2FlbQIxMAABHcDJq8FbbUQJgLtR-HuwIEBknE8PeNannviNIDSoX_yRzFvLqyz9J-HecQ_aem_rTwKR0cWgZa59dGwFw_gEg

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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.