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Deep Magma Flow at the Reykjanes Peninsula

Recent earthquakes on Reykjanes Peninsula show the trend of propagating from west to east. One reason for the earthquakes is magma intrusions, and therefore we should try to understand from where the extra magma is originated. The candidate is the upwelling line of the Reykjanes Ridge. Magma flows into the tectonic plate from the division line, and then horizontally within the polygon. Rifting, aligned perpenticular to surface tectonic features, can occur within the uppermost convection rolls layer at 120 km depth (convection layer 1), due to coupling effect of the next layer below (convection layer 2). This will open the way for molten magma towards SE, until it reaches the border line between the tectonic plates within the southern half of Reykjanes Peninsula. The main two channels within the polygon are found at 1/3 of the length of the NW-side of the polygon (formed by the Reykjanes Ridge Lines), in turn forming, in the long run, the two volcanic systems of Krýsuvík and Brennisteinsfjöll. The Svartsengi volcanic area is formed due to the existence of a division line of layers 3 and 4 directly below, but the origin of intrusions there is probably also magma from the Reykjanes line.

The deep flow of magma (below Moho) from Reykjanes Convection Rolls Division Line towards the relevant volcanic systems. Superimposed on map from the Icelandic Meteorological Office.

This flow (below the Moho discontinuity) results in rising of the surface close to the border line of tectonic plates (black line). This interplay of different convection rolls layers, division of two different tectonic plates, and the resulting seismic area, creates a complicated cycle of volcanism and seismic activity, along with several geothermal sites.

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Identification of Active Volcanic Polygons in Iceland

Iceland is divided into several volcanic zones and belts. Here, a division method according to numbers of polygons is introduced.

Numbers of volcanically active polygons in Iceland

(1) This polygon comprises half of Reykjanes Oblique Rift Zone (RORZ). The western corner connects with the Reykjanes Ridge. (2) The other half of RORZ. The eastern corner connects with the South Iceland Seismic Zone. (3) The southern half of the Western Volcanic Zone. The rifting process is mainly found within the eastern half of the polygon. The Rift Valley of Thingvellir is found there. (4) The northern half of the WVZ. Langjökull Glacier covers a large part of this section. (5) This polygon is a volcanic belt on its own. Formerly, it was the southern end of a much longer volcanic zone extending to Skagafjordur, but that part was replaced by the North Volcanic Zone. (6) The southern part of the South Iceland Volcanic Belt, which contains the Westman Islands. (7) The northern part of the SIVB with Eyjafjallajökull and Katla. Hekla is located on the northern corner of the polygon. (8) The southernmost part of the Eastern Volcanic Zone. The rifting process perpendicular to tectonic drift appears very clearly, and magma is mainly provided horizontally from the adjacent polygons, for instance from Grímsvötn, Bárdarbunga or Katla caldera. (9) The central polygon of the EVZ, filled with powerful volcanic systems. It has adjacent mini polygons of Kverkfjöll and Grímsvötn, and the side system of Tungnafellsjökull. In the middle, Bárdarbunga has played a big role, responsible for the Holuhraun eruption. (11) The southernmost polygon of the North Volcanic Zone. It is actually the turning part between the EVZ and the NVZ, and the pattern forming the polygons becomes less distinct along this latitude. Askja is found in the center of the area. (12) This polygon of Hrúthálsar volcanic site is the central part of NVZ. It is perhaps a bit remote and has not been active recently, so it is not a famous volcanic site. (13) The southern side of the polygon forms a hub for the volcanic and geothermal areas near Lake Mývatn. The northern corner marks the end of the NVZ, It connects with the Grímsey Oblique Rift in the north. (14) This is the southern half of the Öræfajökull Volcanic Belt. It is a bit outside the main volcanic formations of Iceland and is entirely located within the Eurasian Tectonic Plate area. (15) The northern half of the ÖVB, with Snæfell Volcano at the northern end. Snæfell is also curiously a counterpart of Snæfellsjökull in the west of Iceland, found exactly on the same latitude, and in the same context with the mantle convection rolls system (although mirrored). (16) The eastern roots of the Snæfellsnes Volcanic Belt. The Ljósufjöll Volcanic System extends through the area. (17) The central part of SVB, marking the location of Lýsufjöll Volcanic System. (18) The western most part of SVB, with Snæfellsjökull at the western end, being the western outpost of Icelandic Volcanoes, and as mentioned before, the counterpart of the eastern outposts of Icelandic Volcanoes, Snæfell. The Grímsey Oblique Rift has a few volcanic systems, but the polygon system is quite tight at that latitude, so no numbers are given to that area here. The Reykjanes Ridge follows a line, rather than polygons, so it is not included in this numerical system either. Many mini polygons must be analyzed separately but are not included here to maintain some degree of clarity.

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Tectonic Drift Direction and Perpendicular Rifting Process

The Eastern Volcanic Rift Zone is unique and shows the interplay between tectonic drift and rift process. The rifting is perpendicular to the tectonic drift.

The drift vectors ara symmetrical around NS-axis.

The drift in the western half is slightly faster than in the eastern half. The drift vectors tend to be perpendicular to equatorial convection rolls, and thereby the vectors are aligned along the polar convection rolls. Information about the measurements of tectonic drift is found here: https://www.lmi.is/static/files/utgefid_efni/Maelingar/isnet_endurmael_2016_skyrsla.pdf

The rifting perpendicular to basic drift direction results in a row of craters like Lakagígar

This picture is found on a sign in the middle of the Eldhraun Lava Field which did flow in the year 1783.

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Boiling Ground at Mývatn Nature Baths

The Mývatn area is on the plate boundary of North Iceland. In addition, special stress from below is added by mantle currents. Steam leaks from the groun all around the road leading to the Mývatn Nature Baths.

The Mývatn Nature Baths seen in the distance

Exceptional activity as found near Mývatn can be explained, as seen on the map below.

Areas of Mývatn Nature Baths, Bjarnarflag, Krafla, Hverarönd etc.

North-east of Mývatn is a geothermal wonderland, that can only be explained with this line of mantle convection underneath. The line is of double nature, because it both stands for division between small rolls of upper mantle, and also that of the large scale rolls of lower mantle. Mývatn is located directly over the big convection rolls responsible for creating the Atlantic Ocean.

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The Complexity of Reykjanes Oblique Rift Zone

Reykjanes Oblique Rift Zone is one of the most geologically complex areas in Iceland, because it has interwoven volcanic and seismic zone. The strike-slip faults of the seismic zone form due to pressure from SW and NE, whereas the volcanic fissures open when rifting occurs because of pulling from SE and NW. The polygon forming the main part of the Reykjanes Peninsula explains this. Therefore, we can see that different layers of convection rolls can affect the same area simultaneously.

The Reykjanes Oblique Rift Zone Polygon

A map from ISOR has been inserted at the lower right corner to show how the volcanic zones form perpendicular to the drift of the North American Tectonic Plate on one hand, and the opposite small scale effect of the eastern Reykjanes Ridge Convection Roll on the other hand.

The local rifting due to effect of opposite magma flow of the convection current below is found on bothe sides of the division line between N-America and Eurasia, drawn as curved black line through the polygon of Reykjanes Peninsula.

Red lines indicate up-welling division between convection rolls, blue lines are for down-welling.