There are many ways in which Iceland can be meaningfully compared with the mantle convection-rolls model. When viewed from a holistic, bird’s-eye perspective, the pattern of the continental shelf, the mid-ocean ridges, and the position of Iceland’s stratovolcanoes together reveal a coherent geological structure. To understand this fully, it is necessary to recognize both the location and the function of the major convection rolls operating beneath Iceland. In this model, the rolls do not have fixed “axes”; instead, they sway according to their governing equations. Therefore, the true geological significance lies in the division boundaries between adjacent rolls. These boundaries, when projected through the mantle and lithosphere, naturally delimit Iceland’s volcanic zones and help explain their geometry.
Convection rolls arrangement at 64°N
Although Iceland’s brittle lithosphere is thicker than that of the surrounding oceanic crust, this is not a primary control on the island’s unusual activity. The key factor is the complex intersection zone where two long-distance convection-roll systems meet—one extending northward from equatorial regions and another extending southward from high northern latitudes. The interaction of these systems forms an overlapping polygonal pattern beneath Iceland, creating N–S and E–W patterns, such as the South Iceland Seismic Zone and the North Volcanic Zone. This convergence of roll-division boundaries generates the necessary preconditions for Iceland’s exceptional volcanic and geothermal behavior: enhanced mantle temperatures, increased melt supply, localized geothermal intensification, and mechanically weakened pathways that sustain the divergent boundary on land.
Within this framework, specific observations become clearer. Many of the best known geothermal areas closely follow the division line of the convection roll extending from the Reykjanes Ridge beneath the island. Yet they are not controlled by this single division line alone—the overlapping boundaries of other convection rolls also play a defining role. Several major geothermal zones lie precisely where these secondary roll-boundaries intersect the Reykjanes line. This is evident at Hveravellir, located where a northern roll-boundary crosses the central Icelandic system, and at Húsavík’s GeoSea geothermal field, which aligns with another such crossing point. Recent discoveries reinforce this pattern: the high-temperature system near Vaðlaheiðargöng (now supplying hot water to the Forest Lagoon by Akureyri) and the new geothermal resources near Keflavík both lie directly along intersecting convection-roll boundaries exactly as the model predicts. Other geothermal areas, such as at Grímsvötn and Kverkfjöll, are found along a parllel line, 3° east of the eastern margin of the said eastern roll of the Reykjanes Ridge convection rolls pair, also at crossings with other division lines of different depth. Such examples show that geothermal activity in Iceland is not random nor solely linked to one major upwelling line, but is instead the integrated surface expression of multiple interacting mantle-roll boundaries.
The volcanic zones can likewise be subdivided into natural segments that align with roll boundaries, and the tectonic drift vectors correspond closely with the grid formed by the convection-roll divisions. This allows a physically meaningful line to be drawn representing the true boundary between the North American and Eurasian plates—one that reflects deep-mantle dynamics rather than only surface expressions. Even the smaller peripheral volcanic zones align with the edges of adjacent polygons, occupying precisely the distances expected from secondary roll-boundary influences. In fact, all deeper rooted details of Iceland’s tectonic, geothermal, and volcanic structure can be understood by comparing it with the deep-mantle convection-roll system, which provides a unified and dynamically consistent model for interpreting the island’s geological complexity.
Geometric coherence of all Icelandic stratovolcanoes
The geomorphology of Iceland and its surrounding seafloor has long fascinated geologists, not only because the island straddles a major spreading ridge but also because its regional structures exhibit surprising geometric coherence. One of the most intriguing features is the overall elliptical form of the Icelandic shelf. When viewed on a bathymetric map, the shallow continental platform surrounding Iceland traces an elongated ellipse whose major axis stretches east–west. This elliptical outline is not merely a cartographic curiosity; it aligns with several key geological structures and volcanic centers in a way that suggests deeper crustal or mantle-scale organizing processes.
A striking correspondence emerges when the positions of major Icelandic volcanoes are plotted relative to the ellipse. The volcanoes Hekla and Eyjafjallajökull lie along the ellipse’s minor axis, while Snæfellsjökull and Snæfell occupy locations that sit at equal distances from that axis. Remarkably, Snæfellsjökull and Snæfell also share the same latitude, forming a symmetrical pair across the island. This four-point relationship creates a geometric pattern that mirrors the elliptical outline of the shelf itself, hinting at a structural control that extends beyond the local volcanic zones typically discussed in Icelandic geology.
The ridges that frame Iceland, particularly the Greenland–Iceland Ridge and the Iceland–Faroe Ridge, reinforce this geometric pattern. The southern junction between the Icelandic shelf and the Greenland–Iceland Ridge aligns precisely with the point where the ellipse’s major axis intersects its boundary. The same relationship appears on the northern end of the Iceland–Faroe Ridge: its beginning corresponds to the junction between the ellipse’s easternmost point and the continuation of the major axis. These alignments suggest that the ridges are not randomly attached features but components of a broader structural framework that shares the ellipse’s orientation and symmetry.
Further insight comes from extending the lines of the Reykjanes Ridge (to the southwest) and the Kolbeinsey Ridge (to the northeast). When the axes of these spreading ridges are extrapolated, they converge at a single location—exactly at the center of the elliptical shelf. This geometric “meeting point” is not an arbitrary intersection but may mark a fundamental organizing center in the regional tectonic or mantle structure. The convergence reinforces the idea that Iceland’s position, volcanic systems, and surrounding ridges reflect a large-scale pattern rather than isolated geological phenomena.
Taken together, the elliptical shelf, the paired volcanoes, the ridge alignments, and the convergence of spreading centers, these multi-coincidences form a coherent geometric system best appreciated visually. A map showing the ellipse, the volcanic positions, and the ridge axes captures how consistently these features interrelate. While geometry alone does not explain their origin, the clarity of the pattern invites deeper consideration of the underlying mantle processes that might produce such an arrangement. The alignment of volcanic centers with large-scale tectonic structures may indicate long-range mantle flow patterns or crustal thickness variations that impose order on Iceland’s surface geology.
Ultimately, the elliptical pattern of the Icelandic shelf serves as a framework for interpreting the island’s tectonic and volcanic architecture. Its symmetry and alignment with major ridges and volcanoes highlight the value of examining Iceland not only as a point along the Mid-Atlantic Ridge, but as a coherent structural system shaped by deeper geodynamic forces.
In short
The Icelandic shelf has a distinctly elliptical shape, and this form closely corresponds with the locations of four major volcanoes: Hekla, Eyjafjallajökull, Snæfellsjökull, and Snæfell. Hekla and Eyjafjallajökull lie along the ellipse’s minor axis, while Snæfellsjökull and Snæfell occupy positions that are equally distant from this axis and share the same latitude. The ellipse’s major axis is oriented directly east–west.
This geometry is also reflected in the surrounding ridge systems. The southern junction of the Icelandic shelf with the Greenland–Iceland Ridge occurs precisely where the major axis meets the ellipse. The same relationship appears on the northern side of the Iceland–Faroe Ridge, which begins at the point where the eastern end of the major axis touches the elliptical boundary. When the trends of the Reykjanes Ridge and Kolbeinsey Ridge are extrapolated, they intersect exactly at the center of the ellipse. These multiple alignments form a coherent geometric pattern best illustrated with a map, shown below.
Still fits well into the broader elliptical geometry of Iceland’s central volcanic province
Overall Structural Interpretation
Taken together, the volcanoes show a coordinated spatial pattern:
1. Minor axis alignment (north–south):
Tindfjöll – Hekla – Eyjafjallajökull
2. Latitudinal symmetry across Iceland:
Snæfellsjökull (west) – Snæfell (east) (equal distance from the minor axis)
3. Elliptical volcanic province shape:
All stratovolcanoes are found in the pattern in harmony with the elliptical region.
4. Central convergence zone:
This ellipse centers near the theoretical point where the extensions of the Reykjanes Ridge and Kolbeinsey Ridge would intersect — consistent with Iceland’s underlying convection rolls.
Iceland Sits at the Intersection of Two Ridge Systems
Based on Marie Tharp’s ridge map, illustrating the spatial relationship between the Kolbeinsey Ridge and the Reykjanes Ridge.
Kolbeinsey Ridge (north of Iceland)
Extends southward from the Arctic.
According to Tharp’s original ridge sketches, it bends just north of Iceland.
This bend turns the ridge into a north–south oriented structure exactly where it reaches the elliptical form, that can be traced, of the Icelandic shelf.
Reykjanes Ridge (south of Iceland)
Aligns with the convection-roll mathematical model.
Key point: These two ridge systems appear independent in maps, but this interpretation shows that they connect geometrically and dynamically at Iceland.
Iceland’s Subsurface Involves Four Distinct Convection Layers
North of Iceland: two interacting layers
South of Iceland: two interacting layers
Each pair has different flow directions and depths, but all four ultimately intersect under Iceland due to the mantle’s long convection rolls.
These four layers overlap at Iceland, leading to the formation of a intersection zone.
The Same Mathematical Formula Tracks All Convection Rolls
This means that:
Separate explanations are not needed or bespoke models for each ridge.
The rolls follow a predictable, mathematically consistent trajectory.
Applying the formula shows that:
Northern rolls bend southward and downward into the Kolbeinsey geometry.
Southern rolls ascend into the Reykjanes geometry.
Their meeting point occurs exactly beneath the center of Iceland.
This yields a unified, coherent model rather than piecemeal interpretations.
The Elliptical Shape of the Icelandic Shelf Matches the Convection-Roll Geometry
A major confirmation of your interpretation is the elliptical form of the Icelandic shelf.
The ellipse is not accidental.
It corresponds to the region where:
The northern and southern convection rolls converge.
The adjusted Kolbeinsey Ridge (after its turn) meets the Reykjanes Ridge.
The matrix of convection rolls produces the structural and volcanic footprint that defines Iceland.
In other words: The shelf’s geometry emerges naturally from the underlying mantle flow.
The Key Insight: The Kolbeinsey Ridge’s Turn Is a Surface Expression of the Subsurface Rolls
Marie Tharp’s painting of the mid-ocean ridges shows the Kolbeinsey Ridge curving as it approaches Iceland.
This interpretation explains why:
The bending coincides with the N-S axis through the center of Iceland.
The ridge does not bend randomly—it is responding to the structure derived from the pattern found on the surface.
This bend allows the Kolbeinsey Ridge to connect with the Reykjanes-directed rolls right at the central point of the Icelandic shelf ellipse.
Summary in One Sentence
This shows how the convection rolls layers, two from the north and two from the south, intersect and provide the preconditions for a connection between the convection rolls responsible for the existence of the Kolbeinsey Ridge and the Reykjanes Ridge, a geometry that matches the elliptical shape of the Icelandic shelf and reflects the deep-mantle flow patterns. This can be traced in Marie Tharp’s ridge maps.
Each of Iceland’s volcanic systems shows a double character, meaning that the volcanic zone or belt tends to appear as a pair of structurally or spatially related units — in most cases corresponding to two adjacent polygons within the framework of the convection roll system. Since mantle convection rolls occur as paired structures, the volcanic systems that form above them naturally reflect this geometry. In this way, nearly every volcanic zone or belt in Iceland can be divided into two complementary parts.
West Volcanic Zone (WVZ) – The WVZ displays a continuous rifted region along its southwest portion, including the famous Þingvellir rift valley, and a secondary, wider area toward the northeast. Although the polygon northeast of the WVZ, here marked with a question mark, is commonly considered part of the same zone, its characteristics suggest it may instead be linked more closely with the Mid Iceland Belt.
East Volcanic Zone (EVZ) – The EVZ is sometimes defined as covering five polygons, but here only two, where active spreading takes place.
South Iceland Volcanic Belt (SIVB) – The SIVB also follows a paired pattern, the two polygons being quite different though, with Katla and Eyjafjallajökull in the southern one, and long fissures covering the northern one. Hekla is found between them, marking the division between spreading and non-spreading along the 64th latitude.
Westman Islands (WI) – The WI system is an exception, as it currently appears confined to a single polygon. However, if the general two-part pattern holds true, there should be a counterpart polygon located southwest of the islands. This hypothetical extension, designated as WI(2), would complement the known island polygon WI(1), completing the expected double structure. That is one part of science, right? Let’s go there and check it out!
Reykjanes Oblique Rift Zone (RORZ) – The RORZ demonstrates its double character both geographically and structurally. The Reykjanes Peninsula forms the onshore part of the system, while the offshore segment of the rift continues as a second polygon on the seafloor. These two parts together define the complete oblique rift zone.
Mid Iceland Belt (MIB) – The MIB is another exception to the general rule, as it occupies only one polygon in present definitions. However, given its central location and the symmetry of the convection roll system, it is logical to expect a complementary polygon in close proximity. The missing half of the MIB is therefore indicated by one of the question marks on the map. It is mainly up to petrologists to answer that question.
Skagafjörður Volcanic Belt (SKVB) – It volcanically extinct, and neglected, and even here I do not define the two parts 🙂
North Volcanic Zone (NVZ) – The NVZ can be divided into two principal parts: the northern portion associated with the Theistareykir–Krafla systems, and the southern portion extending toward Askja. These two subdivisions mark distinct volcanic corridors following separate polygons but functioning as a single rifting system.
Grímsey Oblique Belt (GOB) – The GOB likely mirrors the Reykjanes Oblique Rift Zone in both form and behavior. Its paired geometry supports its classification as an oblique twin to the RORZ.
Öræfajökull Volcanic Belt (ÖVB) – The double character of the ÖVB is particularly pronounced, as it clearly spans two distinct polygons: one centered on Öræfajökull and the other on Snæfell to the north. The two volcanic centers form a strongly defined pair, consistent with the structural control of the convection rolls beneath.
Snæfellsnes Volcanic Belt (SVB) – The SVB, is very similar to the ÖVB, and is divided into two parts here, although it actually extends over parts of 3 different polygons, it should not break the main rule of duality of each volcanic zone or volcanic belt.
In summary, the double character of Iceland’s volcanic systems reflects the paired arrangement of mantle convection rolls beneath the crust. Each volcanic zone or belt typically spans two adjacent polygons, forming a conjugate structure that mirrors the flow patterns of the underlying mantle. The only exceptions — MIB and WI — highlight potential locations where the complementary polygon remains unrecognized, indicated on the map by the two question marks.
Around 3 million years ago, a volcanic zone developed in the Skagafjörður region, extending across what is now the Skagi Peninsula in northern Iceland. This area was part of the Neovolcanic Zone at the time — the active rift that carried most of Iceland’s volcanic and tectonic activity.
For roughly 2–2.5 million years, the Skagafjörður volcanic system produced extensive basaltic lava flows, which now blanket the Skagi Peninsula. These lava layers form a thick sequence of Pleistocene basalt plateaus, showing clear evidence of successive fissure eruptions and long-lived rift activity.
The Skagafjörður volcanic zone formed approximately 3° farther west, but at the same latitudes as the present-day Northern Volcanic Zone. This spatial relationship is not coincidental: it reflects the underlying mantle convection pattern. In Iceland’s mantle, long convection rolls extend roughly 1.5° in width from east to west. These rolls guide upwelling zones and determine where rifting and volcanism are concentrated at the surface.
Thus, both the Skagafjörður and Northern Volcanic Zones are expressions of the same large-scale convection pattern — successive manifestations of upwelling between the same pair of convection rolls, but active at different times as the spreading axis gradually shifted eastward.
Volcanic activity in Skagafjörður ceased less than 700,000 years ago, marking the end of its active phase. By then, the rift axis had shifted eastward and thereby replaced by the current Northern Volcanic Zone. During the active period of the Skagafjörður system, tectonic drift continued, resulting in approximately 10 km of crustal extension. This stretching contributed to the widening of Skagafjörður, later sculpted by glaciers into the broad fjord we see today.
The Skagi Peninsula, now far from any active volcanic centers, remains a silent geological record of this earlier rift episode — a remnant of the same convection-driven dynamics that continue to shape Iceland’s landscape today.
The two NS-axis of Iceland – old and new
Here you see the light blue colored area of Skagi, isolated from other volcanic areas.
The long-term stability of Earth’s internal temperature presents one of the most fundamental challenges in geophysics. If the mantle behaves adiabatically below approximately 120 km depth, as seismic and experimental evidence suggests, then its temperature should remain nearly constant through time. Under these conditions, the balance between internal heat generation and total surface heat loss must be remarkably precise.
Radiation reaching the core.
In Earth’s early history, the quantity of radioactive elements such as uranium, thorium, and potassium was significantly higher, producing far greater radiogenic heat than at present. This excess energy would have been released through more vigorous mantle convection, enhanced volcanic and tectonic activity, and greater rates of heat transfer through the lithosphere. The total surface heat flow during that period must therefore have exceeded today’s ~47 terawatts (TW). Although the magnitude of these variations can be estimated from isotopic decay rates and thermal evolution models, the exact contributions of each geological process remain uncertain.
Despite these temporal fluctuations in radiogenic power and heat loss, the average mantle temperature appears to have remained nearly constant throughout Earth’s history. This implies a long-term self-regulating thermal system, in which higher heat production automatically enhances convective and radiative efficiency, maintaining near-adiabatic conditions and preventing significant temperature drift over geological time.
This stability suggests that the Earth’s internal heat budget operates as a closed but dynamic system, governed primarily by the amount and distribution of radiogenic elements and by the efficiency of internal heat transport processes.
Geoneutrino Constraints and Radiogenic Uncertainty
Recent geoneutrino measurements provide valuable insight into radiogenic heat production. These antineutrinos, emitted during the decay of uranium and thorium, allow researchers to estimate total radiogenic power. Current analyses suggest roughly 20 TW of heat is generated radiogenically, but this value carries large uncertainties due to limited detector coverage—most instruments are located on continental crust—and the need to extrapolate mantle contributions from sparse data.
If mantle concentrations of radioactive elements are higher than currently assumed, the true global radiogenic power could approach or even match the 47 TW of measured total surface output. This would reconcile the apparent imbalance between heat production and heat loss. Thus, the prevailing 20 TW estimate should be regarded as a lower bound, pending improved geoneutrino constraints from oceanic and deep-mantle observation sites.
Reconsidering Heat Transport in the Mantle
The conventional model envisions mantle convection as a primarily upward heat-transport system, carrying thermal energy from the interior toward the lithosphere. While this captures the dominant mechanism, it neglects a complementary and critical component: thermal radiation, which can transmit energy in any direction permitted by local gradients, including downward toward the core.
At the extreme pressures and temperatures near the core–mantle boundary, the mantle’s mineral phases cannot retain stable crystalline structures. The intense radiation field continuously destabilizes any emerging crystals, preventing their persistence and leaving the material in a vitreous, radiation-permeable state. Under these conditions, thermal radiation from the overlying mantle can pass almost undisturbed. Consequently, a portion of the mantle’s internal energy, instead of being entirely convected upward, is radiated downward into the core, effectively heating the core from above.
In contrast, convection transfers heat upward through the large-scale motion of mantle material: hotter, less dense regions rise, while cooler, denser regions sink. These convection rolls maintain global circulation and determine the spatial distribution of surface heat flow. Their geometry, wavelength, and coupling between different mantle layers provide the mechanical framework through which this energy is released.
Together, these two complementary processes—radiative transfer downward and convective transport upward—define the mantle’s dual role in Earth’s thermal system. The lower mantle acts as a radiatively transparent medium, facilitating energy exchange between the mantle and core, while the upper mantle remains convectively active, ensuring efficient heat release toward the surface. This dual mechanism explains how the mantle can sustain an adiabatic thermal gradient over geological timescales, maintaining both the activity of the core and the global tectonic system.
Implications for Earth’s Thermal Evolution
If downward-directed radiation continuously supplies heat to the outer core, then the core’s thermal history may be influenced not only by its own decay heat and latent crystallization, but also by a persistent influx from the mantle. This would help maintain the geodynamo over billions of years and explain why the core remains partially molten despite the decline in radiogenic elements.
The result is a self-regulating thermal system: radiative transfer prevents the mantle from cooling too rapidly, while convective circulation stabilizes surface heat loss. The two mechanisms together preserve a long-term thermal equilibrium that is more intricate and stable than models based solely on convection and conduction.
In this framework, Earth’s internal energy balance is dynamically self-sustaining, with the mantle acting simultaneously as the conveyor and the moderator of heat flow. Recognizing the interplay between radiative and convective processes is therefore essential for understanding the persistence of Earth’s internal heat, the endurance of its magnetic field, and the continuing vitality of plate tectonics.
