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For the last four decades, about one eruption has occurred every two years in Iceland. Still we know nothing about the next one, Where, when and how questions can not be answered. Something new is surprising us now and then, like Öræfajökull now melting the ice at its top. Rather big earthquakes at Bárðarbunga bring it to our attention again and again. Let us have a look at the list of some of the suspected volcanic sites:

Recently earthquakes shook Skjaldbreið and it seemed like magma was entering the crust a few kilometers below the mountain. Hekla has changed its rhythm, but the mountain has expanded more than before the last eruption. Katla is a mystique: When will the next large scale flood happen?  Bárðarbunga and Grímsvötn are going through a period of activity. Actually Bárðarbunga is the most likely candidate for the next eruption. It is also a very interesting case to study, as it is in the middle of a polygon, showing itself to be a caldera with the function of feeding the spreading zone with magma forming huge dykes to cope with the tectonic drift. Askja can in turn be affected by the dykes propagating from Bárðarbunga. Recently even Kverkfjöll became a suspect when there were signs of eruption found in rivers flowing from that area. And finally, magma must be responsible for the melting of ice at the top of Öræfajökull. We just do not know the details of the intrusion below the mountain.

I mentioned the SISZ earlier, as it is one of the clearest examples of polygons marked by the mantle convection cells. The balanced conditions within the ductile part of the tectonic plate lead to earthquake faults exactly in between the symmetrical lines around it to the NW, NE, SW and SE. The faults are therefore aligned NS.

In this way it becomes much easier to analyze every feature of earthquake zones of this kind. The reasons for pressure directions become clear. In this case, pressure is exerted from NE and SW. NS-faults are drawn with 715 meters interval along the 64th parallel.

This can be called the Vatnajökull Polygon:

At three corners of the main polygon the mantle convection rolls form, there are very famous volcanic sites, Grímsvötn, Kverkfjöll and Öræfajökull. Esjufjöll are found close to the center of the polygon. But the polygon is very unlike the next polygons to the NW and W which are in a rift zone. The Vatnajökull Polygon is very active, but no rifting is taking place within it. The polygon should still move partly as a whole, and therefore activity at Bárðarbunga and especially Grímsvötn and Kverkfjöll might affect Öræfajökull. It is obvious how this polygon provides the main area for Vatnajökull. The line from Öræfajökull to the NE also marks the eastern edge of the glacier. So, the convection rolls far below give us a framework to explain the appearance of the wonder world of  Vatnajökull.

Today there two earthquakes were measured at Bárðarbunga – 3.9 on Richter Scale. Besides that, water from its geothermal areas probably finds it way from there to the river Jökulsá á Fjöllum.

In 2014 the volcanic site of Bárðarbunga erupted. It was called the Holuhraun eruption, because the lava came up to the surface about 45 km away from its place of origin. How can magma flow so far, thereby forming a dyke, and then eurupt? The bedrock around is much colder, cooling the magma down over such a long distance. By looking at a map of convection cell system it becomes understandable.

First the magma did flow to the SE, perpendicular to the rift zone! It is explainable, because the convection cell system under Iceland always provides lines more and less perpendicular to each other forming polygons. Then the magma turned 90° to the NE along the rift zone. When close to the NE edge of the polygon it turned to the north, and on the relevant line turned slightly to the right and over to the next intersection line between two adjacent convection rolls. Then eruption occurred, the largest lava flow in Iceland for 230 years!

The explanation must be that extra magma was added from below, when the dyke material was flowing above the convection rolls line, causing it to erupt.

The drawing shows how I combined information from the Icelandic Meteorological Office Web Site with the lines formed by the convection rolls below. It is curious enough that all the directions resemble calculations, and similar calculations can be repeated for tectonics all around Iceland.