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The 1.5° Spatial Sequence of Iceland

April 26, 2026 Steingrimur Thorbjarnarson

The Active South

Looking closely at southern Iceland, from the Reykjanes Ridge in the west to Öræfajökull in the east, a sequence of 1.5° spatial intervals can be observed. This pattern can be analyzed in detail, as many geological features align consistently within it.

First, the mid-ocean ridge forms a continuous structural trend, including a section approximately 900 km long. The Reykjanes Peninsula can be interpreted as a single volcanic zone, although its westernmost part represents a transition from a side-stepping arrangement of volcanic systems to a more continuous ridge structure.

Within this framework, a polygonal area can be identified that is densely filled with volcanic systems. A southwest (SW) division line within this polygon marks the location of the Blue Lagoon. At present, this line appears to provide a steady flow of magma into the crust, feeding a magma chamber beneath the area. When this chamber empties, eruptions occur along the Sundhnúkur crater row.

A dike intrusion and associated surface deformation have developed along a SW–NE trend, extending across much of the peninsula, from the southern coast toward the area near the road connecting Reykjavík and Keflavík Airport in the north.

To the east, the volcanic systems of Krýsuvík, Trölladyngja, and Hengill are aligned along the same structural trend. The eastern boundary of Hengill is marked by a clear slope known as Hlíð, after which other volcanic systems of the West Volcanic Zone (WVZ) continue along the calculated division line.

These intersections also define the western boundary of the South Iceland Seismic Zone (SISZ), which dominates the next 1.5° interval eastward, extending toward the volcano Hekla.

Hekla lies at a key boundary:

between the SISZ and the East Volcanic Zone (EVZ)
between the divergent tectonic region to the north and the volcanic but non-divergent region to the south

The southern region is therefore often referred to as the South Iceland Volcanic Belt, distinguishing it from the actively rifting EVZ. South of this lies the Westman Islands, which are sometimes treated separately, although they can also be viewed as part of a continuous volcanic system with the EVZ and the southern belt.

As in the West Volcanic Zone, the calculated division line clearly marks the eastern boundary of the EVZ. Across the region, the main volcanic systems consistently align with the pattern expected from underlying convection rolls. The division lines, their intersections, and the polygonal areas all appear to play structural roles. Even the north–south and east–west axes that subdivide these polygons seem to influence volcanic behavior.

A comparable polygonal structure includes the volcanic systems of Katla and Eyjafjallajökull. This has both:

an east–west axis from Katla to Eyjafjallajökull
a north–south axis running from Hekla through Vatnafjöll to Eyjafjallajökull

Eyjafjallajökull lies at the center of this polygon. The 2010 eruption of Eyjafjallajökull can be interpreted within this framework: basaltic magma flowed along the east–west axis from the east into the volcano, triggering an eruption from a more silica-rich magma chamber with a lower melting point.

From the EVZ, another 1.5° step to the east leads to Öræfajökull, the highest volcano in Iceland. A narrow volcanic zone extends northeast from it along a division line. At this location, four inferred convection-roll division lines appear to converge. A similar structural role is observed at Grímsvötn, located to the northwest and also separated by a polygon of 1.5° span from east to west.

There are, of course, many additional details, which are explored in other posts.

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A Convection Roll Model of Earth’s Interior: Layering and Discontinuities – and Iceland

April 25, 2026 Steingrimur Thorbjarnarson

The map used below to indicate the location of convection rolls beneath Iceland is derived from this section of the Earth’s layers. Tracing the process from the consistent thickness of each layer to the exact location of the convection rolls—and thereby constructing a three-dimensional model of the Earth—is, of course, a complex and lengthy task. With this map, however, meaningful comparisons can be made, and a few are outlined below.

Convection roll model showing the discontinuities at 120, 410, and 670 km, along with the relevant layers;
the lower mantle contains two sets of rolls, each 15° wide.

A geological map of Iceland can then be compared with the model:

Map base: https://jokull.jorfi.is/articles/jokull2008.58/jokull2008.58.197.pdf

This map shows the location of both the Reykjanes Ridge and the Kolbeinsey Ridge. Although the map is a simplification and is neither fully accurate nor perfectly aligned with the calculated grid, a few features can still be immediately observed:

1. Volcanic zones match the grid.
Those familiar with the geology of Iceland will notice that the sharp boundaries of the volcanic zones correspond closely with the division lines between convection rolls. The distinction between upwelling and downwelling also clearly influences the distribution of these volcanic zones. Furthermore, the pattern defined by the division lines has explanatory value: the differing orientations of the East Volcanic Zone and the North Volcanic Zone are consistent with the distinct grid patterns observed in the southern and northern halves of Iceland.

2. Seismic zones match the grid.
The South Iceland Seismic Zone, as identified through geophysical measurements, is located between Hekla and Hveragerði, precisely within one of the polygons defined by the grid. The Tjörnes Fracture Zone also aligns with the division-line pattern observed along the northern coast.

3. Distribution of geothermal areas.
The distribution of geothermal areas also corresponds with the model. Low-temperature areas are associated with specific polygons and tend to cluster within them. In contrast, high-temperature areas are associated with division lines, their intersections, and the boundary between the Eurasian Plate and the North American Plate.

4. Local tectonic alignment within polygons.
Tectonic features within the polygons, such as volcanic fissures, are aligned according to the geometry of each polygon, reflecting the structure imposed by the convection rolls. These alignments do not follow the general direction of plate motion, suggesting that the model explains a major structural trend not accounted for in previous models.

5. NW–SE and NE–SW fissure patterns.
In some cases, fissures exhibit a NW–SE alignment consistent with the mirrored structure of the underlying convection rolls. Different layers display different roll orientations, while maintaining symmetry relative to the north–south axis. The coexistence of NW–SE and NE–SW trends has not been satisfactorily explained by other models.

Many additional aspects of consistency between the model and surface expressions have been discussed here.

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April 24, 2026April 24, 2026 Steingrimur Thorbjarnarson

The difference between a typical mid-ocean ridge and Iceland can be described as a contrast between a purely divergent process and a more resistant one.

The two ridges to the north and south of Iceland are clearly related, forming parts of what is generally known as the Mid-Atlantic Ridge. However, they are given specific names: the Reykjanes Ridge in the south and the Kolbeinsey Ridge in the north. Iceland is often said to lie on the Mid-Atlantic Ridge, but this can sound misleading, as it is actually situated between these two ridge segments.

If we consider the nomenclature of these sections individually, we can divide the system into three parts from north to south: the Kolbeinsey Ridge, Iceland, and the Reykjanes Ridge. The volcanic zones of Iceland perform the same role in terms of tectonic drift and divergence as the ridge crests do along the mid-ocean ridges. However, these zones are much broader than the narrow rift valleys typically found at ridge tops. This is especially evident in southern Iceland, where two parallel zones, the East and West Volcanic Zones, are present, along with a third adjacent system, the Öræfajökull Volcanic Zone. In northern Iceland, the North Volcanic Zone is currently singular, but a few hundred thousand years ago it was accompanied by a parallel structure, the Skagafjörður Volcanic Belt.

These differences can be better understood by considering mantle flow. At mid-ocean ridges, the sharp, narrow divisions at the ridge crest suggest that tectonic plates diverge with relatively little resistance. In contrast, the development of wide volcanic zones in Iceland indicates a different process occurring at depth.

This type of rifting appears to result from resistance: the surface plate motion is not fully aligned with the underlying mantle flow. While the large tectonic plate moves in one direction, local mantle convection may flow in the opposite direction. This interaction creates resistance, and it is this resistance that leads to broader and more complex rifting zones.

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Northerly Flowing Rivers of North Iceland: Indicators of Tectonic Structure

April 23, 2026 Steingrimur Thorbjarnarson

The northerly flowing rivers of northern Iceland provide an intriguing window into the deeper tectonic and geological structure of the region. North of Iceland lies the Kolbeinsey Ridge, a spreading ridge that exerts a significant influence on the country’s geology. Unlike the Reykjanes Ridge, the Kolbeinsey Ridge does not visibly intersect or “reach” the Icelandic mainland. Nevertheless, its structural imprint is evident.

The ridge exhibits a pronounced north–south (N–S) orientation, and this same directional trend can be observed across much of northern Iceland. One of the most compelling expressions of this alignment is seen in the river systems. Major rivers such as Hrútafjarðará, Héraðsvötn, Eyjafjarðará, Skjálfandafljót, Jökulsá á Fjöllum, Hofsá, and Lagarfljót largely follow northerly courses, reflecting a structural control that is unlikely to be coincidental.

In addition to their general N–S alignment, these rivers display occasional deviations that appear to coincide with subtle structural boundaries or division lines in the crust. These interruptions in flow direction may mark transitions between different tectonic domains or the influence of underlying mantle dynamics.

The estuaries of these rivers further reinforce this pattern. Their distribution shows a striking regularity that aligns with the proposed grid of convection rolls beneath Iceland. Each estuary can be interpreted as forming a “hub” within this grid, suggesting that surface hydrology may be responding to deeper, organized mantle processes. This spatial consistency lends support to the idea that convection rolls patterns influence not only volcanic and tectonic features, but also the development of drainage systems.

A careful comparison of topographic and geological maps with the river network makes these relationships more apparent. The rivers are not randomly distributed; rather, they appear to trace out an underlying structural framework. In this sense, northern Iceland’s river systems may serve as surface indicators of deeper geodynamic organization (the grid formed by mantle convection rolls), reflecting the combined influence of the Kolbeinsey Ridge and broader mantle convection patterns.

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Consistency between the Reykjanes Ridge and Tectonics of Iceland

April 22, 2026April 23, 2026 Steingrimur Thorbjarnarson

The Reykjanes Ridge is the dominant structural feature in the geology of Iceland. Its importance lies not only in its scale, but also in the way it appears to express a broader tectonic principle that influences much of the country’s geological architecture.

The Reykjanes Ridge Equation: $(x – C_n)^2 + (y – 32)^2 = 35.34^2$

On the map, a red line traces the continuous (holistic) segment of the Reykjanes Ridge, extending for roughly 900 km. What is particularly notable is that this line can be described by a simple geometric relationship (of relevant degrees of latitude x and logitude y. In this case Cn = -7.66): $(x – C_n)^2 + (y – 32)^2 = 35.34^2$ This is not merely a mathematical curiosity. In the southern half of Iceland, several major rivers and geomorphological features align closely with this same trend. Among the most prominent examples are Norðurá, Hvítá, and Þjórsá, as well as the lake Langisjór. Many additional rivers, lakes, and volcanic features follow these orientations across southern Iceland.

South Iceland and the Reykjanes Ridge.
Upwelling lines are red, downwelling lines are blue.

This alignment is not a new observation. It is widely recognized that Iceland’s rivers and tectonic features often follow consistent directional trends, and this has long been apparent to geologists and observers alike. However, what is less commonly emphasized is that this pattern can be captured, and better understood, through a specific mathematical form such as the equation above.

Lake Langisjór looking toward N42°W, calculated according to the curve: $(x – C_n)^2 + (y – 32)^2 = 35.34^2$

Seen in this light, the alignment is not just descriptive but diagnostic. It points toward an underlying organizing mechanism. The interpretation proposed here is that convection rolls beneath the lithosphere are arranged in a geometry that gives rise to this pattern at the surface.

If the Earth’s interior consisted of only a single layer of convection rolls, the resulting surface pattern would likely be much simpler and more direct. In reality, multiple layers and interacting systems of mantle flow are involved, which complicates the expression of these structures at the surface. A full treatment of these layered interactions is beyond the scope of this discussion. Nevertheless, the essential idea can be understood by focusing on one layer, which includes the pair of convection rolls shaping this section of the Reykjanes Ridge.

A useful way to visualize this is to imagine convection rolls arranged side by side, like parallel cylinders. In this framework, the Reykjanes Ridge occupies precisely a boundary between two of those rolls, and its path follows the equation given above with notable accuracy. At Iceland’s latitudes, tectonic activity becomes more diffuse. Instead of being confined to a narrow ridge, divergence is distributed across broader volcanic zones. This produces a wider ara of deformation, magmatism, and surface restructuring. As a result, the structural signal of the underlying convection is expressed not only with a single line, but across a much wider region.

This broader influence is clearly reflected in the landscape. The rivers of southern Iceland do not flow randomly; their courses frequently align with the same geometric trend as the Reykjanes Ridge. When viewed from this perspective, their paths are not merely shaped by local topography, but are part of a larger, coherent tectonic pattern. Recognizing this connection is important. Everyone knows this trend, but general trend is not the same as accurate mathematical equation. This is how over a century of accurate measurements and mapping can be used to take an additional step towards understanding tectonics of the surface, and of course the inner structure of the Earth.