Magic Magma

The volcanoes of Eyjafjallajökull and Katla are among the most famous volcanic systems in Iceland. They occupy a prominent position in the geology of South Iceland and have long attracted attention because of their apparent connection. Historically, eruptions of the two volcanoes have often occurred within relatively short intervals of one another, suggesting that some form of interaction may exist between the neighboring volcanic systems.

Eyjafjallajökull, an east-west aligned elliptical volcano,
with a glacial tongue flowing northward from the summit crater.
(https://www.visindavefur.is/svar.php?id=77035)

Geological maps reveal a remarkable east-west arrangement extending across the region. Katla lies beneath Mýrdalsjökull to the east, while Eyjafjallajökull forms an elongated volcanic edifice immediately to the west. The volcanic structures, fissure swarms, and associated tectonic features display a pronounced east-west alignment.

Eyjafjallajökull itself is an elliptical volcano. Its fissure swarm follows the long east-west axis of the edifice, indicating that the orientation is deeply rooted in the tectonic framework of the area. At the western end of this axis lies Seljalandsfoss, one of Iceland’s best-known waterfalls. At the eastern end, the glacier tongue of Kötlujökull marks the outlet area where meltwater and jökulhlaups from Katla most commonly emerge.

This eastern opening is particularly significant. When Katla erupts beneath its ice cover, large floods are generated. These floods frequently escape through the Kötlujökull outlet, effectively utilizing the same east-west corridor that connects Katla with Eyjafjallajökull. The repeated use of this pathway suggests that the axis represents a long-lived structural weakness within the crust.

Within the framework of the mantle convection rolls model, this east-west trend coincides with the central axis of a polygon formed by convection-roll division lines. In this interpretation, the geometry observed at the surface reflects deeper patterns within the mantle. The Eyjafjallajökull–Katla axis occupies the center of one such polygon, while other volcanic systems define its boundaries and corners.

Polygonal pattern formed by mantle convection roll division lines. According to the model, volcanic zones,
tectonic boundaries, and major geological features tend to develop along these persistent structural lines.

The north-south arrangement of volcanic centers is equally intriguing. Hekla occupies a prominent position to the north-east, while Vatnafjöll lies between Hekla and Eyjafjallajökull. Drawing a line through Hekla, Vatnafjöll, and the summit crater of Eyjafjallajökull reveals a clear north-south trend. According to the mantle convection rolls interpretation, this line represents another major axis of the same polygon.

The north-south axis and east-west axis through Eyjafjallajökull.

When viewed in a broader context, the north-south alignment does not end in South Iceland. Similar trends can be traced along the Mid-Atlantic Ridge, which itself forms one of the most prominent north-south geological structures on Earth. Extending the same geometric framework to a global scale, the trend can be followed toward the Southern Ocean and ultimately to the minor axis of the elliptical form of Antarctica identified elsewhere in this study.

Whether examined locally or globally, Eyjafjallajökull and Katla occupy a unique position within Icelandic geology. Their historical relationship, their shared east-west structural alignment, the pathway of Katla’s jökulhlaups, and their position within larger tectonic patterns all point toward an underlying degree of geometric organization. The volcanoes are not merely neighboring volcanic systems; they appear to form part of a larger structural framework extending across Iceland and beyond.

The Eyjafjallajökull–Katla connection therefore provides an excellent example of how local volcanic features can be examined within a wider geodynamic context. The geological observations themselves are well established. The challenge is to understand whether these observations are isolated phenomena or components of a larger pattern linking Icelandic volcanism to the geometry of mantle processes on a planetary scale.

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South Iceland Seismic Zone — A Geometric Link Between Iceland’s Rift Systems

May 27, 2026May 27, 2026 Steingrimur Thorbjarnarson

Iceland Seismic Zone — A Geometric Link Between Iceland’s Rift Systems

The South Iceland Seismic Zone is one of the most remarkable tectonic regions in Iceland. It is not only a zone of frequent earthquakes, but also a key to understanding how stress, volcanic systems, and crustal deformation interact across the island. While the volcanic zones of Iceland often receive most public attention, the seismic zone between them reveals an equally important part of the tectonic structure.

The mantle convection rolls division lines polygon
framing the South Iceland Seismic Zone.

The zone stretches across southern Iceland, roughly between the western volcanic systems near Hengill and the eastern systems connected with Hekla and the East Volcanic Zone.

The hypothetical sequence of north-south aligned earthquake faults
superimposed on a map of the South Iceland Seismic Zone.

Unlike the volcanic rift zones, where extension is expressed through volcanism and fissure swarms, the South Iceland Seismic Zone mainly releases tectonic stress through earthquakes.

Simplified map showing earthquake and volcanic zones of Iceland.

A Transform Zone Across Iceland

In plate tectonics, Iceland is usually described as a place where the Mid-Atlantic Ridge rises above sea level. The North American and Eurasian tectonic plates move apart across the island. However, the spreading is not expressed as one single continuous rift. Instead, the volcanic zones are offset from each other.

The South Iceland Seismic Zone acts as a transfer structure between these volcanic segments. In standard tectonic terminology, it is often described as a transform zone, although it differs from classical oceanic transforms because deformation is distributed across a broad area rather than concentrated along one fault.

The earthquakes of the zone commonly occur on north-south oriented faults, even though the broader tectonic movement across Iceland is mainly east-west extension. This apparent contradiction is one of the most interesting aspects of the region.

The Diamond-Shaped Geometry

One of the clearest large-scale geometric features of the seismic zone is its tendency toward polygonal organization. The region can be interpreted as a broad diamond-shaped area between volcanic systems.

The eastern and western ends connect naturally with major volcanic centers, to the west: the Hveragerði geothermal region, and to the east at Hekla and the western margin of the East Volcanic Zone

Within this framework, stress appears to organize itself along lines that connect opposite corners of the polygonal area. The result is the repeated formation of north-south fracture structures inside an overall east-west tectonic setting.

This is one reason why the South Iceland Seismic Zone is so important geologically. It demonstrates that tectonic deformation is not simply linear. Instead, it becomes organized into geometric structures where local stress fields redirect movement into highly regular patterns.

Earthquakes and Historical Activity

The South Iceland Seismic Zone has produced many destructive earthquakes throughout Icelandic history. Some of the strongest historical earthquake sequences occurred in this region, affecting farms, churches, and settlements across the lowlands.

Notable earthquake episodes include:

The great earthquakes of 1784
The 1896 earthquake sequence
The June 2000 earthquakes
The May 2008 earthquakes

The earthquakes are usually shallow, which increases their impact at the surface. Even moderate earthquakes can therefore produce significant shaking.

Connection With Hekla

Hekla occupies a uniquely important tectonic position at the eastern end of the seismic zone. It lies where several tectonic tendencies intersect:

Connecting the South Iceland Seismic Zone and the East Volcanic Zone
A key function within the regional spreading across Iceland
Direct north-south structural alignments

Because of this, Hekla can be viewed as both a volcanic center and a tectonic focal point.

The geometry becomes especially interesting when Iceland is examined together with its continental shelf and offshore ridge systems. The South Iceland Seismic Zone appears not merely as a local fracture belt, but as part of a broader structural organization extending into the North Atlantic.

A Broader Geometric Interpretation

The South Iceland Seismic Zone also provides an opportunity to examine tectonics through geometric relationships.

The repeated north-south fracture orientation inside a broader east-west tectonic environment suggests that deformation is influenced by organized stress fields rather than random faulting alone. Similar geometric tendencies can be observed elsewhere in Iceland, particularly where polygonal crustal blocks form between volcanic systems and fracture zones.

In the mantle convection rolls interpretation, these polygonal structures emerge naturally from the division lines between adjacent convection cells. Pressure along the sides of such polygons can produce fracture systems that connect one corner to another, generating north-south alignments within larger east-west tectonic regions.

Whether examined through conventional tectonics or broader geometric models, the South Iceland Seismic Zone remains one of Iceland’s clearest examples of how crustal deformation organizes itself into remarkably regular patterns.

A Geological Laboratory

Few places on Earth allow such direct observation of active tectonics as Iceland. In the South Iceland Seismic Zone, earthquakes, volcanic systems, geothermal areas, and visible surface fractures all interact within a relatively compact area.

The landscape of southern Iceland preserves these processes in extraordinary clarity. Every earthquake sequence adds another chapter to the evolving tectonic story of Iceland.

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Hawaii at the Center of the Global Tectonic Pattern

May 23, 2026 Steingrimur Thorbjarnarson

It is well known that the African Tectonic Plate has been drifting relatively slowly compared with many of the surrounding plates. On the opposite side of the globe, the Pacific Plate also appears exceptional in several respects. At its center lies Hawaii, one of the most volcanically active regions on Earth.

Theoretic Pacific-centered tectonic map emphasizing the approximately equal spacing
of the Mid-Atlantic Ridge and Mid-Indian Ridge relative to Hawaii.

The S-shaped red lines show the location of the divisions, according to the mantle convection rolls model, associated with the minor and major axes of Antarctica. When the globe is viewed from a Pacific-centered perspective, with Hawaii near the middle of the map, an interesting geometric relationship appears. The theoretical central axes of the Mid-Atlantic Ridge and the Mid-Indian Ridge lie at equal distances from Hawaii. This relationship can best be illustrated with a world map centered on the Pacific Ocean.

In such a representation, the three major mid-ocean ridge systems — the Mid-Atlantic Ridge, the Mid-Indian Ridge, and the East Pacific Rise — together with the principal subduction zones of the western Pacific, appear geometrically connected with the endpoints of the major and minor axes of the elliptical form associated with the Antarctic Tectonic Plate.

Within this framework, Hawaii occupies a particularly central position. It lies midway between the axial region of the Pacific spreading system, represented by the East Pacific Rise, and the extensive subduction systems of the western Pacific Ring of Fire. Seen in this way, Hawaii becomes part of a broader large-scale geometric arrangement linking the Pacific basin, Antarctica, and the global mid-ocean ridge network.

This concept can be illustrated effectively with a Pacific-centered world map, where Africa appears on both outer edges of the projection, emphasizing the symmetry and large-scale relationships of the global tectonic system.

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The Function of Indonesia’s Subduction Zones and the Caribbean Subduction and Transform Zones within the Ring of Fire

May 23, 2026May 23, 2026 Steingrimur Thorbjarnarson

Comparing the geometry of Indonesia and the Caribbean reveals a remarkable degree of similarity. Although these two tectonic systems are located on opposite sides of the Pacific realm, many of their large-scale structural relationships appear comparable.

The Identical Shape of Indonesia and the Caribbean:
Comparable Subduction and Transform Geometry on Opposite Sides of the Ring of Fire

First, both systems are closely associated with the equatorial region. The Indonesian arc faces southward, with one important eastern endpoint located near the coast of Sumatra. Another major subduction-related crossing appears roughly 30° farther east along the equatorial zone, connected with the subduction framework surrounding the Philippine Plate.

A similar arrangement can be observed in the Caribbean region, although shifted slightly north of the equator. The Caribbean basin is associated with another pair of crossings of lower-mantle flow structures, where subduction-related zones occur at points approximately 30° apart, comparable to the Indonesian case. The Caribbean arc also extends outward in a manner resembling the Indonesian arc.

The Central American Trench stretches from the inner part of the Ring of Fire toward its outer margin, where the division line appears to turn toward the key region of the Peru–Chile Trench near the equatorial framework. This geometry resembles the relationship between the New Guinea Trench and the continuation of the Philippine Trench on the Indonesian side of the Pacific.

In this way, many aspects of the Indonesian and Caribbean plate-boundary systems appear strikingly similar, although effectively rotated by 180° relative to one another.

Considering that these two tectonic regions connect the Pacific Ocean with the Indian Ocean and the Atlantic Ocean respectively, the broader function of this arrangement becomes important to examine. The fundamental span of a 30° convection-roll unit, together with an additional extension east of the eastern crossing points, may help explain the tectonic importance of these paired regions on opposite sides of the Ring of Fire.

South of Indonesia, subduction is the dominant tectonic process, whereas in the Caribbean region transform motion and tectonic transition play a larger role, especially along the northern boundary of the Caribbean Plate. Even so, both systems appear to participate in a broader structural unity within the Ring of Fire.

The anticlockwise rotational tendency associated with the North American sector of the Ring of Fire is consistent with the northward-facing curvature of the Caribbean arc and the southward-facing curvature of the Indonesian arc. At the same time, the long-term expansion of the Atlantic Ocean on one side and the Indian Ocean on the other appears to be buffered near equatorial latitudes by these major subduction and transform systems situated between the large ocean basins.

The similarities are therefore sufficiently striking that they may partly reflect an underlying large-scale geometric organization. At the same time, this comparison leaves many important questions unanswered and suggests several directions worthy of further investigation. Further information: https://pangea.stanford.edu/ERE/db/GeoConf/papers/SGW/2024/Thorbjarnarson.pdf

All of these characteristics of the two archipelagic systems are, of course, well known. They can first be summarized as follows:

Both archipelagos are associated with the Ring of Fire.
Both archipelagos are located close to the equator.
Both archipelagos have a predominantly east–west orientation.

However, when compared within the framework of the mantle convection rolls model, several additional observations can be made:

When the tectonic features of Central America are included, the overall mathematical framework becomes directly comparable to that of Indonesia.
The width of both archipelagic systems is comparable when measured in degrees of longitude along their respective latitudes.
The relative position of both archipelagos appears comparable in the context of the large-scale convection-roll geometry proposed in the mantle convection rolls model.

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From Antarctica to Iceland and Yellowstone: A Geometric Framework

May 22, 2026May 22, 2026 Steingrimur Thorbjarnarson

The influence of mantle convection upon the Earth’s surface can be examined through the tectonic patterns that develop above it. In this study, several recurring geometrical expressions are considered. First are the division lines between convection rolls. Second are the polygonal regions enclosed by those division lines, where geological structures frequently develop from one corner of a polygon to another, commonly in north–south or east–west directions. A third recurring expression is the appearance of elliptical forms under certain large-scale conditions.

These observations suggest that many aspects of geology may be investigated through geometric analysis. Once geometric consistency is identified, detailed geographic and geoscientific data can be used to further evaluate the resulting patterns and their possible physical significance.

The Pacific Ring of Fire provides an important example. Although the exact physical processes governing its overall geometry remain uncertain, the arrangement itself displays remarkable large-scale regularity. Antarctica presents a similar challenge. Its tectonic framework is difficult to explain in simple terms, yet its geometry also appears highly organized.

Antarctica is particularly difficult to examine because most world maps distort the continent, stretching it along the southern edge of the map projection. When viewed directly from above the South Pole, however, its remarkably circular form becomes evident. It is also well known that Antarctica can be divided into East and West Antarctica, with the western sector being considerably more tectonically and volcanically active.

The boundary between East and West Antarctica appears to coincide closely with the center of the minor axis of the system of mid-ocean ridges encircling the continent. Near this axis lies the famous volcano Mount Erebus, one of the most persistently active volcanoes on Earth. Because Erebus is located at approximately 77.5°S latitude, its distance from the inferred minor axis is only about 100 km.

Another important geometric relationship emerges offshore from Erebus. At this location, the minor axis of the Antarctic system appears to intersect the minor axis of the Pacific Ring of Fire. Thus, the most active volcano in Antarctica occupies a position where two large-scale tectonic geometries appear to converge: the minor axis of the Antarctic ring of mid-ocean ridges and the minor axis of the Ring of Fire.

This geometric axis can then be examined further in relation to external geological conditions. When the Antarctic minor axis is extrapolated northward, it intersects the inner margin of the Ring of Fire at the location of the Valley of Geysers on the Kamchatka Peninsula. A similar relationship appears when extending the major axis of Antarctica northward toward the East Pacific Rise, where the projected line crosses the region of Yellowstone National Park, also situated at the geometrical margin of the Ring of Fire.

These two regions, Kamchatka and Yellowstone, contain by far the greatest concentration of geysers on Earth. Beyond them, only a few additional major geyser regions exist worldwide, and these too may potentially be interpreted within a similar geometric framework, such as Iceland. New Zealand is another obvious example.

The implication is not necessarily that geometry alone explains tectonic activity, but rather that persistent mantle organization may leave detectable large-scale geometric expressions at the Earth’s surface. Such relationships may provide an additional tool for examining the long-term structure of mantle convection and its connection to volcanism, tectonics, and geothermal activity. The degree of accuracy is very high, only to be understood in context with the mathematics of the shape of the Earth.

For more details: https://pangea.stanford.edu/ERE/db/GeoConf/papers/SGW/2024/Thorbjarnarson.pdf