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Downwelling means a tendency to converge, and upwelling means divergence. The small scale convection rolls intervene with the main trend following the large convection cells of lower mantle. That main line lies through the middle of the country from SW to NE. The two southern volcanic zones, called WVZ and EVZ, are found within the same settings, namely with upwelling to the west and downwelling at the eastern side. The reason is conflict between the tectonic drift to the NW and the opposite trend resulting from the upwelling and downwelling lines.

The MIVZ in central Iceland actually also has this setup, but to the NE and SW. The shift of tightness of the polygons at 65°N results in almost continuous volcanic areas from Snæfellsjökull to Snæfell. Then there is the NS-axis from Öræfajökull to Axarfjörður, besides the less known NS axis from Eyjafjallajökull through Hekla to Drangey.

How to explain the existence of the EVZ and Katla volcanic system? We can analyze it by looking at the convection cell system, its lines and polygons. Katla takes over two polygons as shown here:

The four lines are all downwelling. The caldera is found in the east corner of the southern polygon. When magma finds its way out of the caldera, it flows along the fissures exactly from one side to another of the northern polygon. The tension is created by the conflict between large scale tectonic drift, pulling from NE to NW, and the small scale (1.5° wide) pulling of the uppermost convection roll under the EVZ from NW to SE.

To see this more clearly, zoom in a bit:

The violet color shows Katla Volcanic System, both caldera and the fissure swarm extending to the NE. The other fissure swarm, extending from NE to SW, is the Grímsvötn system, where the caldera is also found adjacent to a corner of the relevant polygon.

 

The North Volcanic Zone is differs from the WVZ and EVZ in the south. It is aligned directly NS as a whole, but individual volcanic systems point slightly to the NE. Comparing the grid to the map of National Land Survey of Iceland gives this picture:

The vectors of tectonic drift as mesures for ISNET 2004 are divided around the NS-oriented NVZ. By marking the main polygons of the zone red, the main volcanic areas are seen to be found within them, thereby functioning to meet the tectonic drift as these polygons break up, making space for more magma input from below.

The directional effect on tectonics resulting from diverging to the east and west on the polygons is thereby quite obvious.

There are seven volcanic zones in Iceland. Let us analyse that on a simplified map. The volcanic zones can be described according to convection rolls pattern. (Four different layers of convection rolls cut through the ductile part of tectonic plates with Muroe Effect at the division lines, creating this pattern of polygons. It is the same law of physics as used for shaped charges.)

First, the Reykjanes Volcanic Belt (RVB) is found within a polygon, bending to the next polygon to the SW, forming the end of the Reykjanes Ridge.

The West Volcanic zone is related to a polygon in the western highlands, and does occupy it fully.

A more complete picture is shown when the half the adjacent polygons are combined with the main WVZ polygon. To understand better, we can have a look at an old map as a base:

This map shows the connection between the WVZ, RVB and RR. The third layer of the intersection zone is shown. (It is the upper most layer for most of the globe, from equator to 60.7°N and 60.7°S.)

Let us keep on with the wholistic comparison:

The Mid Iceland Volcanic Belt is represented by the central polygon, only slightly extanding out of that area, mainly in the southern part of the next polygon to the east.

The East Volcanic Zone shows very strong resemblance with the convection rolls pattern. It can be explained, as the upper most roll is extending from NE to SW under that area. The mantle flow is mainly from west to east, pulling the crust apart, playing the main role of tectonic drift at those latitudes.

The North Volcanic Zone is aligned NS, and the axis can be shown with a single line.

To further clarify how the zone follows the NS-symmetric pattern of polygons, the main ones are pointed out here.

Finally, the outer limits of the NVZ are drawn through the central axis of the peripheric polygons.

Finally, the two outposts of volcanic zones, the Snæfellsnes Volcanic Belt and the Öræfajökull Volcanic Belt are shown. The endpoints are Snæfellsjökull and Snæfell, and those two outposts of Icelandic volcanoes are found on the same latitude, in the same settings compared with the convection rolls pattern.

More accurate comparison can be made with more precise maps, such as this one:

The accuracy of division lines and mapping of surface features becomes obvious. The SISZ and Tjörnes Fracture Zone can also be connected with certain polygons and lines.

Marking up a few features can clarify a few things:

The convection rolls extending from SW to NE are quite dominant, but at around 65°N, where the effect of the other convection rolls becomes more apparent, and the pattern becomes more complicated, a sharp turn to the north occurs. the NVZ has several volcanic systems arranged in an en echelon pattern directly to the north. Then the Tjörnes Fracture Zone obviously follows the convection rolls aligned SE-NW of the equator system.

In this way, the volcanic zones can be compared with the convection rolls under Iceland.

Drawing the Earth with its layers in correct proportions:

Inner core, outer core, Gutenberg layer, 410 km discontinuity, 250 km discontinuity, tectonic plate bottom line at 120 km depth, surface with radius 6371 km.

Six currents added to outer core, with equal hight and bredth. It coincides with the outer limits of the Gutenberg layer.

Convection rolls sections added with same hight and bredth to the lower mantle. They coincide with the lower limits of Gutenberg layer and 410 km depth from surface.

The convection rolls sections are further identified with vertical lines where they are divided from each other.

The remaining layers are also filled with convection rolls sections, with identical height and bredth. The section of the convection rolls model is thereby ready.

This is how it works 🙂

Then this is traced to the north and south, and finally compared with the surface and our general knowlede about the Earth, based on measurements, physics and calculations.