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The Large Eruptions of Eldgjá 939 and Laki 1783

Steingrimur Thorbjarnarson

The two major fissure eruptions of Eldgjá (939 CE) and Laki (1783 CE) display several striking similarities. The eruptive fissures are broadly parallel and occur within the same general region of southern Iceland. Lava from the Laki eruption partly overlies lava produced during the earlier Eldgjá event..

Despite these similarities, the eruptions are associated with different volcanic systems. The Eldgjá eruption is linked to the Katla volcanic system, whereas the Laki eruption belongs to the Grímsvötn system. These central volcanoes are separated by approximately 120 km. Remarkably, the Laki crater row lies almost exactly midway between the two calderas.

Both calderas also coincide with intersections of the structural division lines shown on the map. The dykes responsible for the eruptions propagated along the structural line situated between the two calderas, forming fissures that follow the same general orientation. This geometry shows that the regional stress field and crustal structure guide magma transport over large distances.

In both cases, the propagating dyke appears to cross a perpendicular structural division located between the two volcanic systems. The onset of eruption occurs shortly after this crossing. This recurring pattern suggests that the intersection between these structural elements plays an important role in controlling where magma reaches the surface.

One interpretation is that the perpendicular division represents a zone of enhanced crustal permeability, where fractures or weaknesses allow magma within the dyke to ascend more easily. Another possibility is that this structural boundary marks a deeper source region where additional hot magma is supplied from below. In this case, the propagating dyke may intersect a region of increased magma pressure or temperature, destabilizing the system and triggering eruption.

Along the Ring Road, informational displays describe the severe consequences of the 1783 Laki eruption. Images depict the suffering experienced by the Icelandic population during the event. Another image refers to the French Revolution, illustrating the wider climatic and societal effects of the eruption.

Images representing Laki eruption.
Image related to the French revolution.

The volcanic haze produced by Laki spread across large parts of Europe, contributing to crop failures and famine. These environmental stresses intensified social tensions in France and are considered one of the contributing factors to the unrest that culminated in the French Revolution.

These two eruptions are did affect the history of Iceland more than any other volcanic events.

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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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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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Seeing the Invisible: Visualizing Mantle Convection Rolls with AI

Steingrimur Thorbjarnarson

Visualizing mantle convection rolls becomes significantly easier with the use of AI-based three-dimensional models. What were once abstract concepts—difficult to imagine and even harder to communicate—can now be rendered as coherent flow structures extending through the mantle. These visualizations provide an important bridge between mathematical models of mantle dynamics and the geological features observed at Earth’s surface. Here is a beginning:

AI-made simplified version of convection rolls under Iceland.

Understanding mantle convection is essential if we are to understand nature correctly. When long-lived convection rolls are taken into account, the spatial distribution of volcanism, rift zones, and seismic belts becomes more intelligible. Location of volcanoes and earthquake zones can be explained, and mid-ocean ridges are not randomly distributed features; instead, they align along sections that can be calculated, and notably, the same mathematical framework can be used to trace subduction zones.

Iceland is exceptionally well suited for testing this type of model. Few regions on Earth display such a concentration of geological features within such a limited area. This makes it possible to compare predicted mantle-flow patterns directly with mapped surface expressions. AI-generated 3D visualizations allow these comparisons to be made more intuitively, helping to explain how the geometry of convection rolls corresponds to volcanic zones and rift systems.

The functioning of mantle convection rolls is not immediately intuitive and requires time to grasp. The mantle behaves neither as a simple liquid nor as a rigid solid. Instead, temperatures are close to the solidus, allowing slow but organized flow to take place over geological timescales. Molten magma—which may eventually erupt as lava at the surface—is originally supplied along the division lines between adjacent convection rolls, where hot mantle undergoes partial melting and ascends through the tectonic plate.

A model showing correct proportions of the convection rolls along 64°N.

These rolls exert a direct influence on the tectonic plates above them. Through basal traction, the organized mantle flow causes tectonic drift. In most cases, the direction of mantle flow reinforces the dominant tectonic drift. However, in certain regions, a smaller convection roll may locally oppose the main trend of plate motion. When this occurs, extensional stresses can develop in the overlying crust, leading to rifting.

Such rifting is not merely conceptual but measurable. Over time, an active rift zone does typically span 1.5 degrees from east to west. The East Volcanic Zone in Iceland provides a clear example. Its width, orientation, and volcanic productivity are consistent with localized interaction between mantle convection rolls.

By combining mathematical descriptions of mantle flow with AI-based visualization and geological observation, mantle convection rolls can be treated as physically coherent structures linking Earth’s deep interior to its surface expression. Rather than being abstract or speculative, they offer a unifying framework for understanding why geological features appear where they do.