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Large Scale Convection Rolls of Lower Mantle

The convection rolls of lower mantle cover 30° from east to west. The Polar and Equatorial parts of the total system intersect each other. The result is that below the 64th parallel, there must be a division within the lower mantle at the depth around 1655 km. The best place on the surface to represent this, is where the two division lines of lower mantle coincide over divergent plate boundaries, namely at the town of Hveragerdi.

Hveragerdi, with steam rising from hot springs.

On the map, here below, the two division lines between convection rolls have been marked. The blue line shows the lower convection rolls (below 1655 km depth), and the black line shows the upper convection rolls division line (above 1655 km).

This can be difficult to visualize at first. The lower rolls are actually subducted north of 60.3°N. Hveragerdi has also four layers of small scale convection rolls in between 120 and 410 km depth. The combined effect of these division lines creates these special surroundings above.

Lower mantle main convection rolls division lines.
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Continuing the Axis of North Iceland Volcanic Zone and the South Iceland Seismic Zone along 64th Parallel

The spectacular Öræfajökull is found at the 64th parallel, and is by many considered to be located east of the main systems of volcanism in Iceland.

Fjalljökull of Öræfajökull Volcano in Iceland.

Fjalljökull Glacial Tongue, which slides into the Fjallsárlón Lagoon, shown above, is close to the famous Jökulsárlón, or Glacier Lagoon. These places are found east of the highest volcano in Iceland, Öræfajökull. It is actually responsible for some of the most powerful eruptions in Iceland throughout its written history. So what is the context of this outstanding volcanic site?

The location is shown in context with the central line of Reykjanes Ridge (RR), Reykjanes Oblique Rift Zone (RORZ), South Iceland Seismic Zone (SISZ), and North Volcanic Zone (NVZ). Also, the Borgarfjörður Transverse Fault Zone (BTFZ) is shown, Snæfellsnes Volcanic Belt (SVB), West Volcanic Zone (WVZ), East Volcanic Zone (EVZ), South Iceland Volcanic Belt (SIVB), the volcanically extinct Skagafjörður Volcanic Belt (SKVB), Tjörnes Fracture Zone (TFZ) and Grímsey Oblique Rift (GOR).

The simple extension of these two of the main axis traceble of activity in Iceland, leads to the heighest mountain in Iceland. It is the starting point of Öræfajökull Volcanic Belt, extending between Öræfajökull and the dormant volcano Snæfell in Eastern Iceland. As for the polygon pattern, it closely resembles the names given to the various volcanic and seismic areas in Iceland.

Therefore, when thinking about the edge of the EVZ as the blue, double line of downwelling between different convection rolls, we still have to consider a hidden connection from one corner to the other of the relevant polygons, with a very special volcano, Öræfajökull.

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Almannagjá at Thingvellir in Iceland – there for a reason!

The rift valley of Thingvellir is found at the point where the western edge of the West Volcanic Zone of Iceland intersects the N-S axis of the relevant polygon of mantle convection rolls division lines. The location is shown here:

The location of Almannagjá of Thingvellir Rift Valley

The Rift Valley is the most valued of any place in Iceland, the No. 1 National Park, established in 1930 on the occasion of the 1000th anniversary of the National Assembly of Althingi. Usually, the part of the Rift Valley called Almannagjá is filled with visitors, but this time not, during summer 2020.

Almannagjá

The cliffs to the west mark the western boundary of the West Volcanic Zone. Within the Volcanic Zone, this area is a part of the Hengill Volcanic System. According to the Convection Rolls System, the SW-NE alignment of the Volcanic System, and the N-S axis of the Thingvellir Polygon, intersect here. The polygon has a basic trend of breking up along the N-S axis, so therefore the Rift Valley of Thingvellir becomes specially prominent in this area.

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Equator and The Great Rift Valley

The arrangement of sea and landmass along equator is regular as shown here:

The location of The Great Rift Valley at equator

The pattern along equaor of 30° span of S-America, 60° span of Atlantic Ocean, 30° of Africa from west coast to Great Rift Valley, 60° from Great Rift Valley to Indonesia, 30° from west coast of Indonesia to east coast of Indonesia, is quite obvious. Moreover, the pattern fits with the arrrangement of convection rolls within the mantle, considering that mantle material convects in rolls of equal hight and width under balanced conditions of flow.

The proof is found with the location of the Great Rift Valley, as it is not found in context with coast-to-coast distance, but from the west coast of Africa over to a geological phenomena within the continent, that is clearly there due to the inner forces of Earth.

To further examine the distribution of geological features, one can ‘zoom in’ on the Great Rift Valley, and see how it does comply in detail with the upper most convection rolls, close to the tectonic plate.

The double system of Great Rift Valley.

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The Double Nature of the African Great Rift Valley

At equator, the Great Rift Valley is divided into two main parts, described in Wikipedia: https://en.wikipedia.org/wiki/Great_Rift_Valley. The western rift, called Albertine Rift and the eastern rift, called Gregory Rift, together span 9° from east to west along equator. The convection rolls responsible for the formations are shown here:

The convection rolls beneath the two sections of Great Rift Valley.

Each convection roll spans 1.5° from east to west, making the effects on the surface quite understandable. The rifting process is therefore subject to three upwelling sites, whereas the outer margins are marked by downwelling division lines between mantle convection rolls.

Note: A tectonic plate is 120 km thick structure, with a brittle upper part and ductile lower part. The transformation from the rigid structure of tectonic plate, to the flowing nature of mantle material takes place 120 km below the surface. Therefore, adiabatic temperature gradient is found below 120 km depth (described in: Volcanoes: A Planetary Perspective: Written by Peter Francis, 1993 Edition, Publisher: Clarendon).