Tag: geology

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Snaefellsnes Peninsula – Iceland

Steingrimur Thorbjarnarson

The Snæfellsnes Peninsula is a particularly remarkable region of Iceland because it hosts three distinct volcanic systems aligned roughly east–west across the peninsula. Two of these systems have very similar names. The easternmost system is Ljósufjöll, and the central one is Lýsufjöll. Both names carry essentially the same meaning: “the light-coloured mountains.”

This name refers to the relatively silica-rich rock types found in these systems. Compared to many other volcanic areas in Iceland that are dominated by darker basaltic compositions, these systems contain a higher proportion of evolved, more silicate-rich rocks. The lighter coloration of the rhyolitic and dacitic components gives the mountain ranges their distinctive appearance and explains the origin of the names.

An additional noteworthy feature lies beneath the town of Stykkishólmur. The town receives geothermal hot water from a fracture zone whose orientation corresponds closely with predicted structural alignments derived from the convection rolls model of mantle flow. According to this interpretation, a deep-seated division line, representing a boundary between adjacent long convection rolls in the mantle, generated stress conditions favorable for fracture formation in the overlying crust. The present-day geothermal circulation would then be a surface expression of this deeper structural control.

At the same time, the surface morphology of the peninsula has been strongly modified by repeated glaciations. Glacial erosion has carved valleys and lineaments that follow a different dominant alignment. Interestingly, this second alignment also corresponds to another predicted set of division lines within the convection rolls model. In other words, both the geothermal fracture system and the glacially sculpted surface features appear to reflect deep structural patterns rooted in mantle convection dynamics.

Taken together, the volcanic distribution, geothermal fracture orientation, and glacial lineaments on the Snæfellsnes Peninsula may therefore represent multiple surface expressions of a deeper, organized mantle flow structure.

The town of Stykkishólmur:

Here it is on the map:

The town is heated with water from this fracture:

The surface is shaped according to another set of lines, also to be calculated:

On the westernmost tip of the Snæfellsnes Peninsula, Snæfellsjökull rises prominently above the surrounding landscape. This glacier-capped stratovolcano dominates the region both visually and geologically, forming a dramatic landmark at the edge of the Atlantic Ocean. Its symmetrical form and ice-covered summit make it one of Iceland’s most recognizable volcanoes.

Near its slopes once stood the home of Guðríður Þorbjarnardóttir, one of the most remarkable women of the Viking Age. Around the year 1000, she traveled with her husband to Vinland, where she lived for three years. During that time, she gave birth to her son, Snorri Þorfinnsson, who is considered the first European child born in the New World. Vinland is the old Icelandic name of the part of North America found south of Helluland (Baffinland) and Markland (Labrador), centuries before Columbus sailed over the Atlantic Ocean.

On the other side of the glacier, this painting shows Columbus in Iceland:

Behind them rises Snæfellsjökull, the glacier-capped volcano that inspired Journey to the Center of the Earth by Jules Verne. In Verne’s novel, the entrance to Earth’s interior is hidden within the crater of Snæfellsjökull, transforming this already dramatic volcano into a literary gateway to the planet’s deepest mysteries.

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From Iceland to Norway: The Recurring 30° Signature

Steingrimur Thorbjarnarson

The distance between central Iceland and the coastal regions of Norway corresponds to 30 degrees of longitude along the relevant parallels near 64°N. Within the framework of the mantle convection roll model, this spacing is consistent with a predicted division between adjacent lower-mantle flow rolls.

Interestingly, the Norwegian coastline closely follows the calculated lower-mantle division line. This correlation is significant, particularly because many major petroleum fields are located along the Norwegian continental margin. From a geological perspective, the precision of this 30° spacing is striking.

Moreover, the seismic distribution of Norway appears to reflect this structure, as earthquake activity is concentrated along this same zone.

A similar longitudinal distance appears elsewhere in the Atlantic system. At the equator, the distance between the Mid-Atlantic Ridge and the west coast of Africa is also approximately 30°. Furthermore, the Atlantic Ocean spans about 60° of longitude between the estuary of the Amazon River in South America and the African coast. The recurrence of these angular distances, 30° and 60°, suggests a possible large-scale structural regularity in mantle dynamics.

The Iceland–Greenland relationship presents a related but slightly more complex case. An additional rifting episode occurred between Baffin Island and Greenland during the opening of the Labrador Sea and Baffin Bay. Remarkably, the distance between the west coast of Greenland and central Iceland is also 30°. This may indicate that division lines between major convection rolls tend to align with continental margins, particularly at key latitudes such as the equator and around 64°N.

Another notable geometric relationship is that the Bering Strait lies 180° east (and west) of the Norwegian coast, placing it on the opposite side of the globe along a great-circle alignment. The Bering Strait is not found to be responsible for any rifting process, it just happens to be flooded, but according to the convection rolls model, a division below of the lower mantle, is found there!

Mainland of Eurasia 180 at 64N - 02

Elaboration on the Geodynamic Implications

Several implications follow these repeated 30° intervals:

1. Preferred Longitudinal Spacing of Convection Rolls

A 30° spacing corresponds to 12 divisions around the globe (360° / 30° = 12). This reflects a stable wavelength of large-scale lower-mantle convection rolls. Such rolls impose long-lived stress fields on the lithosphere, influencing rifting, margin formation, and sedimentary basin development.

2. Continental Margins as Surface Expressions of Mantle Boundaries

If lower-mantle division lines localize lithospheric weakness, continental breakup and passive margin formation may preferentially occur above them. This can help explain:

  • The Norwegian margin petroleum provinces
  • The Greenland–Baffin rift system
  • The equatorial South America (30°) – Atlantic Ocean (60°) – Africa (30° Great Rift Valley) – Indian Ocean (60°) – Indonesia (30°) – Pacific Ocean (150° Ring of Fire) symmetry.

3. Seismicity Concentration

The observation that Norwegian seismicity aligns with the inferred mantle boundary at the abyss strengthens the argument that deep mantle structures can influence intraplate stress fields.

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The Mississippi River, Oceanic Ridges, and the Geometry of Mantle Convection Rolls

Steingrimur Thorbjarnarson

Mathematics of Mississippi River

One of the recurring observations in the mantle convection rolls model is that major surface features, both continental and oceanic, are not randomly distributed. Instead, they appear to follow large-scale geometric divisions of mantle convection rolls.

A compelling continental example is the Mississippi River system, as shown below:

The thick lines, one of which closely follows Mississippi, represent the large-scale lower mantle convection rolls as shown here:

The Mississippi River representing a Mantle Division Line

The Mississippi River follows a remarkably linear north–south corridor that coincides with deep tectonic segmentation of the North American lithosphere. Along this corridor lies the New Madrid Seismic Zone, one of the most significant intraplate seismic regions in North America.

In the conventional framework, intraplate earthquakes are often treated as localized structural reactivations. However, when viewed through the mantle convection rolls model, the Mississippi corridor may represent a lithospheric expression of a deeper mantle division line. The seismicity is then not anomalous, but a surface response to organized mantle flow beneath the continent.

This interpretation gains strength when examined geometrically.

At latitude 37°N, two reference points illustrate a striking longitudinal spacing:

  • 37° 0.000’N, 90° 0.000’W — Mississippi River region
  • 37° 0.000’N, 30° 0.000’W — Mid-ocean ridge near the Azores Triple Junction

The second point lies along the Mid-Atlantic Ridge, 60° of longitude east of the Mississippi reference. This spacing is consistent with the calculated division intervals derived from large-scale convection roll geometry.

The Mississippi River corridor and the Mid-Atlantic Ridge segment near the Azores thus occupy corresponding positions within the roll framework, one expressed in continental lithosphere, the other in active oceanic spreading.

Extending the Pattern: Juan de Fuca and Reykjanes

The pattern does not stop there, as two additional ridge systems , the Juan de Fuca Ridge and the Reykjanes Ridge, are also located along mathematically calculated mantle convection roll division lines.

These two ridges show notable geometric consistency with one another:

The Reykjanes Ridge forms the northern extension of the Mid-Atlantic spreading system toward Iceland, while the Juan de Fuca Ridge represents an active spreading center in the northeast Pacific. Despite their geographic separation, their placement within the roll division geometry suggests they are not isolated features but components of a larger, organized mantle system, exactly 90° apart from each other.

A Unified Interpretation

When these features are considered together, a coherent spatial pattern emerges:

  • The Mississippi River tectonic corridor
  • The New Madrid Seismic Zone
  • The Mid-Atlantic Ridge near the Azores Triple Junction
  • The Reykjanes Ridge
  • The Juan de Fuca Ridge

All align within a consistent framework of mathematically derived mantle convection roll divisions.

This alignment suggests that:

  1. mantle convection rolls structures exert a primary control on lithospheric segmentation.
  2. Oceanic spreading centers and continental intraplate seismic zones may represent different surface expressions of the same deep mantle flow boundaries.
  3. Intraplate activity along the Mississippi is not an exception to plate tectonics, but a predictable outcome of organized mantle roll geometry.

Rather than viewing mid-ocean ridges, triple junctions, and intraplate seismic zones as separate tectonic phenomena, the convection roll model places them within a unified dynamic system.

Implications

If these correlations are structural rather than coincidental, they imply that mantle convection rolls operate at a scale capable of organizing both continental drainage corridors and oceanic spreading centers.

The Mississippi River, often treated purely as a surface hydrological feature, may therefore trace a deep mantle boundary. The Azores Triple Junction and associated Mid-Atlantic spreading segment may represent the oceanic counterpart of the same geometric division. The Juan de Fuca and Reykjanes ridges further reinforce the repeating pattern.

In this framework, Earth’s surface geometry reflects a deeper, mathematically structured mantle circulation, one that integrates ridges, faults, triple junctions, and intraplate seismicity into a single coherent system.

The accumulating consistency among these examples adds to the growing collection of geological features adhering to the mantle convection rolls model.

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Reykjanes, West Volcanic Zone, Húsavík Fault, and Grímsey Oblique Rift as Surface Expressions of a Single Mantle Convection Roll

Steingrimur Thorbjarnarson

The convection roll bridging the gap between Reykjanes Ridge and Kolbeinsey Ridge

The West Volcanic Zone (WVZ) and the Húsavík–Flatey Fault (HFF) can be understood as two fundamentally different surface responses to the same mantle convection roll, whose flow direction is opposed to the absolute motion of the overlying plate. Where this roll is effectively coupled to the lithosphere, its opposition to plate motion promotes either extension or shear, depending on local boundary conditions.

Mantle Convection Roll at 120 km depth.

Map base: https://www.vedur.is/skjalftar-og-eldgos/frodleikur/greinar/nr/450

The WVZ represents the extensional response to this roll–plate opposition. South of approximately 65° N, the uppermost convection roll maintains sufficient mechanical coupling to the lithosphere to drive sustained rifting and volcanism. Northward of this latitude, however, the polygonal pattern of roll-division lines becomes increasingly complex, and the uppermost roll progressively loses its grip on the plate above. As a result, the rift architecture of the WVZ terminates, and extension is no longer the dominant mode of deformation.

These conditions prevail until the system reaches the HFF. At this location, the same convection roll appears to regain effective coupling to the lithosphere, but now in a geometrical setting defined by a lower division line of the asthenosphere. The result is not extension, but efficient dextral strike-slip motion, localized into a narrow, long-lived fault zone. The HFF thus represents a shear-dominated expression of the same roll–plate opposition that elsewhere produces rift volcanism (RPR, WVZ and GOR). The area south of HHF freely drifts with the North American Tectonic Plate (a smooth displacement of 60 km has been measured). North of the HHF, things are still a bit more complicated.

North of the HFF, a small number of polygons form a region with less seismic activity in which deformation is limited and distributed neither as rifting nor as focused volcanism. Farther north, beyond the next division line parallel to the HFF, the system enters the domain of the Grímsey Oblique Rift (GOR). This boundary lies east of the division associated with the Kolbeinsey Ridge (KR), and therefore clearly within the Eurasian Plate.

Within the GOR domain, the same convection roll continues to influence deformation, but in a setting where tension is created as the North Volcanic Zone (NVZ) fissure swarms extend to the east of the GOR. The GOR is therefore trapped between the Kolbeinsey Ridge and the northern most part of NVZ. This leads to the formation of a volcanic area, linking the NVZ with the Kolbeinsey Ridge. Here, shear and extension are combined, and as a consequence, both seismic activity and volcanism become widespread. Volcanic systems within the GOR represent the volcanic manifestation of this distributed deformation, while seismicity reflects ongoing strain accommodation across the polygonal framework.

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The Mid-Iceland Belt

Steingrimur Thorbjarnarson

The Mid-Iceland Belt (MIB), also referred to as the Central Iceland Volcanic Zone, forms the volcanic connection between the West Volcanic Zone (WVZ) and the East Volcanic Zone (EVZ). Although the precise outlines of individual volcanic systems—particularly those associated with Hofsjökull and Kerlingarfjöll—vary somewhat between published maps, the overall geometry of the belt is consistent.

Within the Mantle Convection Rolls Model, the MIB occupies a central polygon bounded by division lines separating adjacent convection rolls. In addition, many tectonic maps depict a plate-boundary trace aligned approximately east–west through the MIB, reinforcing its interpretation as a zone of plate-scale interaction rather than a simple rift segment.

The Mid-Iceland Belt Polygon

Why the MIB differs fundamentally from WVZ and EVZ

The adjacent volcanic zones, WVZ and EVZ, can be interpreted as rifting zones located above convection rolls whose flow direction opposes the absolute motion of the overlying plate. In those zones, mantle flow and plate motion combine to promote sustained extension and focused rift volcanism.

The MIB does not fit this configuration. Located between the opposing roll-controlled rift systems, it occupies a region where this rifting mechanism does not apply directly. Its existence therefore cannot be explained as a primary spreading axis driven by roll-opposed plate motion. Instead, the MIB must be understood as a structural connection zone accommodating the transfer of deformation between the WVZ and EVZ.

Analogy with the South Iceland Seismic Zone

It has often been noted that the MIB performs a role analogous to that of the South Iceland Seismic Zone (SISZ). The SISZ is characterized by tectonically driven strike-slip and oblique faulting, accommodating lateral plate motion rather than sustained rift volcanism. The MIB is broadly parallel to the SISZ and occupies a comparable central position within its convection-roll polygon.

Between the polygons associated with the SISZ and the MIB lies an intermediate polygon, here referred to as the Hreppar Polygon (HP). Some interpretations treat the SISZ and HP—together with adjacent areas, often including the western margin identified as the Þingvellir rift—as a distinct tectonic microplate. In this framework, the northern boundary of that microplate coincides with the transition across the MIB.

Internal complexity of the MIB polygon

The MIB polygon itself displays a dual structural character. In its southern half, the bounding division lines of the convection rolls converge closely, producing a relatively unified structural pattern. Farther north, these division lines diverge, and an additional micro-polygon appears in the north corner. In this area, fissure swarms extending from the Hofsjökull central volcano exhibit an orientation that differs from that of the southern MIB, indicating localized reorganization of stress.

Comparison with the Tjörnes Fracture Zone

A useful comparison can be made with the Tjörnes Fracture Zone. Within the TFZ, the Húsavík–Flatey Fault accommodates almost exclusively horizontal dextral motion and has done so continuously for millions of years, producing a cumulative offset on the order of 60 km on each side. In contrast, the Grímsey Oblique Rift exhibits both seismic and volcanic activity. Although it is broadly parallel to the Húsavík Fault, it serves a different function: accommodating the combined tectonic and magmatic processes required to link the North Volcanic Zone with the Kolbeinsey Ridge.

In an analogous manner, the SISZ and the MIB together form a paired system: one zone primarily accommodating horizontal tectonic motion, the other incorporating significant volcanic processes.

Latitudinal variation in polygon patterns

The geometric arrangement of convection-roll polygons differs markedly between southern and northern Iceland. In the south, large and relatively regular polygons give rise to east–west-oriented structures, with one zone dominated by horizontal shear (the SISZ) and another incorporating volcanism (the MIB). In the north, the polygon pattern instead permits the development of a single, long-lived, continuous transform fault, represented by the Húsavík–Flatey Fault. Within the adjacent row of polygons, the Grímsey Oblique Rift fulfills the volcanic role associated with plate-boundary connection.

Closing synthesis

Taken together, these observations suggest that the Mid-Iceland Belt is neither a simple rift nor a conventional transform zone. Instead, it represents a mantle-controlled connection zone, complementary to the South Iceland Seismic Zone in the south. The pair of MIB and SISZ is analogous in function to the Grímsey Oblique Rift and Húsavík Fault in the north. The geometry of the MIB, internal complexity, and relationship to adjacent volcanic zones are best understood in terms of the spatial organization of mantle convection rolls rather than solely through plate-boundary kinematics.