Blog

Iceland comprises several volcanic zones that partially intersect and overlap. One of these, the North Volcanic Zone (NVZ), is distinguished by a generally north–south alignment, expressed through en-echelon volcanic systems and long fissure swarms that extend both northward and southward beyond the traditionally mapped limits of the zone.

When interpreted within the framework of the Mantle Convection Rolls Model, the NVZ can be defined with comparatively high geometric precision. A key reference is the Reykjanes Ridge division line, which can be extended mathematically across Iceland. This line intersects the terminal regions of the Tjörnes Fracture Zone, coinciding with the eastern limits of the epicentral swarms associated with the Húsavík–Flatey Fault Zone and the Grímsey Oblique Rift. The same division line also marks the termination of the Reykjanes Peninsula Volcanic Zone, where it merges with the Reykjanes Ridge itself.

At the southern end of Iceland, a second well-defined boundary occurs near 64.9° N, within a narrow latitudinal band south of this line. Here, a pronounced and abrupt change in volcanic and tectonic alignment is observed, involving the West Volcanic Zone, the Central Iceland Volcanic Zone, and the sharp bend separating the NVZ from the East Volcanic Zone.

Taken together, these two geometrically and dynamically constrained boundaries imply that the NVZ can be defined with high precision as the volcanic domain bounded to the south by approximately 64.9° N, and to the north by the Reykjanes Ridge division line intersecting the terminal epicentral swarms of the Húsavík–Flatey Fault Zone and the Grímsey Oblique Rift.

In this study, volcanic zones are defined exclusively on the basis of volcanic architecture and mantle-scale organization, rather than seismic fault systems or plate-boundary kinematics.

The 65th parallel, extending from the Snæfellsnes Volcanic Belt eastward to Snæfell and the surrounding region, is here divided into three equal segments.

The western segment, referred to as the Snæfellsnes window, extends eastward to Reykholtsdalur, an area notable for hosting Deildartunguhver, the most powerful hot spring in the world, with a natural discharge of approximately 180 liters per second of boiling water. The second segment, equal in size, spans the region between Reykholtsdalur and the western boundary of the East Volcanic Zone. The third segment includes Snæfell and its surrounding volcanic features. Notably, this eastern window occupies a position that is geometrically mirrored relative to the Snæfellsnes window when evaluated within the defined division framework. The locations of Hekla and Eyjafjallajökull further illustrate the symmetry inherent in this configuration.

The motivation for emphasizing this observation lies in a particularly robust spatial constraint: Snæfellsjökull and Snæfell are located at exactly the same latitude. In addition, both volcanic centers are positioned at equal distances from Hekla volcano and its north–south–oriented axis. This coincidence is independent of any applied rotation and therefore represents an objective geometric relationship rather than a constructed one. Furthermore, when mirrored, both volcanic centers align with the same division-line grid, suggesting that their placement within their respective volcanic belts is not arbitrary.

Snæfell is geologically separated from the East Volcanic Zone (EVZ), as it belongs to the Öræfajökull Volcanic Belt. Nevertheless, the Snæfellsnes Volcanic Belt and the corresponding section of the EVZ are compared here as structural counterparts within this geometric framework. In addition, the Langjökull volcanic systems within the West Volcanic Zone and the Hofsjökull system within the Mid-Iceland Volcanic Belt—represented here by a single polygon—can be compared using identical window dimensions centered on the north–south axis defined by Eyjafjallajökull and Hekla.

At this latitude, five volcanic zones are intersected, all of which conform to the convection-roll division lines as outlined here. The 65th parallel is also of particular importance because it coincides with a regional transition from predominantly NE–SW-oriented volcanic and fissure systems to a primarily N–S orientation.

Although geometric similarity alone cannot establish causation, the degree of correspondence observed in this analysis supports the internal consistency of a model based on geophysically constrained layer thicknesses within the Earth and the physics of mantle convection. In particular, these observations are consistent with the hypothesis that mantle convection rolls, together with the associated regional stress-field symmetry, exert a first-order control on the spatial organization of volcanic zones in Iceland.

The two parallel volcanic regions of Iceland—the Reykjanes Ridge together with the Reykjanes Oblique Rift Zone and the West Volcanic Zone—form a continuous tectonic structure. A second, parallel structure is found approximately 1.5° farther east and consists of the Vestmannaeyjar (Westman Islands), the South Iceland Volcanic Belt, and the East Volcanic Zone. These two volcanic lineaments are compared here.

The parallel geometry of the two structures is discussed, followed by a closer look at their internal details. The western set of volcanic systems is divided into polygons 1A–6A, while the eastern set is divided into polygons 1B–6B.

Comparison of individual polygons

1A and 1B:
Polygon 1A represents the northern end of the Reykjanes Ridge before it turns westward. Polygon 1B contains the Vestmannaeyjar volcanic system.

2A and 2B:
Polygon 2A still represents the Reykjanes Ridge and includes the first volcanic systems on the Reykjanes Peninsula. Polygon 2B contains Eyjafjallajökull, Katla, and several additional volcanic centers of the South Iceland Volcanic Belt.

3A and 3B:
Polygon 3A contains numerous volcanic systems arranged in a clear en echelon pattern. The westernmost system is Hengill, which extends into polygon 4A. The combined active areas of polygons 3A and 3B span approximately 1.5° in an east–west direction. The Grímsvötn volcanic system extends into polygon 3B and then turns sharply southward into the next polygon.

4A and 4B:
Polygon 4A contains two volcanic systems, both located in the western half of the polygon. A structural shift is evident here: instead of the Reykjanes Ridge being aligned along the western boundary of the polygon set, the volcanic systems are now aligned along the eastern boundary. Þingvellir National Park lies near the center of this polygon and is commonly interpreted as a clear expression of plate divergence.
In contrast, polygon 4B is almost completely filled with volcanic systems, dominated by the Grímsvötn and Bárðarbunga systems.

5A and 5B:
Polygon 5A is dominated by Langjökull and its associated volcanic systems. These systems occupy a wider zone than those in polygon 4A but are still concentrated toward the western side of the polygon. Polygon 5B is again densely populated with volcanic systems, including Grímsvötn in the south, Kverkfjöll in the east, and Bárðarbunga near the center.

6A and 6B:
Polygons 6A and 6B belong to the two parallel volcanic belts, but in both cases the tectonic alignment of fissures and volcanic systems changes at this latitude. North of polygon 6A lies the extinct Skagafjörður volcanic zone, which is not shown on the map because volcanic activity ceased there several hundred thousand years ago. Polygon 6B marks the onset of the North Volcanic Zone, which is aligned directly northward.

Interpretation

The observed geometry and continuity of these volcanic belts can be explained by the presence of long-lived mantle convection rolls beneath Iceland. The two parallel A and B polygon sets are connected by a transitional region, often referred to as the Mid-Iceland Belt. Examination of the details shows that the division lines correspond closely to the southern and northern limits of volcanic activity within this region.

This framework provides a clearer understanding of volcanic activity in Iceland. The two parallel volcanic structures are particularly well suited for analysis and interpretation. The next step is to examine the remaining volcanic zones, including Snæfellsnes, Öræfajökull, North Iceland, and Grímsey.

Dividing the Ring of Fire into eight approximately equal sections reveals a remarkable symmetry.

1. Cascadia and western Canada, extending southward to the San Andreas Fault.
2. California and the Middle America Trench.
3. The Nazca Plate and the Peru–Chile Trench.
4. The main volcanic region of Antarctica.
5. The section containing Mount Erebus.
6. An exceptional segment, where most tectonic and volcanic activity occurs inside the outer elliptical structure. This includes the Tonga–Kermadec Arc, with New Zealand located on the minor axis between sections 5 and 6.
7. The Philippine Plate, where the eastern plate boundary extends beyond the inner ellipse.
8. The island arcs of the Aleutian and Kuril Islands. Japan lies near the major axis, while the Hawaiian Islands extend outward from the north–south axis of the elliptical structure.

The outer ellipse is defined by connecting equatorial trench locations at the coasts of Indonesia and South America, specifically the Philippine Trench and the Peru–Chile Trench.

The origin of this horizontally oriented elliptical geometry is not immediately obvious; however, the San Andreas Fault represents a key constraint. Along this fault, motion is smooth and continuous where the minor axis intersects the inner ellipse, reflecting a kinematic balance between the westward drift of the North American continent and the motion of the Pacific Plate.

This geometric framework also incorporates Yellowstone, which lies at the outer intersection of the minor axis, with New Zealand forming its opposing counterpart.

Earth’s rotation is clearly a primary factor in shaping these large-scale patterns. The geometry can also be meaningfully compared with the convection-rolls model, suggesting a deeper, organized structure beneath the observed surface tectonics.

Here is my essay about the Ring of Fire for further reading: