The geothermal activity of central North Iceland can be divided into three main sections: Skagafjörður, Eyjafjörður, and the Mývatn region. Skagafjörður was an active and distinct volcanic zone until a few hundred thousand years ago, after which the main rifting and volcanic activity gradually shifted eastward.
The distribution of geothermal activity in central parts of Norht Iceland
Eyjafjörður, however, remains an important area of geothermal utilization. Significant activity is found there, particularly in the Hjalteyri geothermal field, which produces around 110 liters per second of hot water. This accounts for roughly 60% of the heating supply for Akureyri, a town of about 20,000 inhabitants and often referred to as the capital of North Iceland. The use of geothermal energy here highlights how Iceland effectively harnesses subsurface heat for sustainable urban development.
Further east lies the Mývatn region, one of the most volcanically active areas in the country, centered around the Krafla volcanic system. This area has experienced numerous eruptions in historical times, including the well-known Krafla Fires in the 18th century and rifting episodes in the late 20th century. The region is characterized by high-temperature geothermal systems, extensive lava fields, pseudocraters, and active fissure swarms.
Geothermal and volcanic activity in this region continues northward beneath the surface, extending all the way to the ocean in Öxarfjörður. This follows the active plate boundary between the North American and Eurasian tectonic plates, part of the Mid-Atlantic Ridge system that crosses Iceland.
Knowing the location of convection rolls of different layers, the geothermal activity can be analyzed in more detail than previously possible. The impact of horizontal drift of the tectonic plates on one hand, and that of vertical effect of ascending magma on the other hand can be studied, and besides that local effect of horizontal flow of magma within particular convection rolls can be taken into account. Understanding those three main factors, geology becomes much more understandable.
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.
Study area of South Iceland
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.
Study area of South Iceland enlarged
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.
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.
The volcanic systems of Reykjanes
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.
A number of Iceland’s most well-known geothermal and bathing sites appear to follow a striking spatial pattern. They can be interpreted as lying along a convection roll situated on the eastern side of the Reykjanes Ridge.
These sites form two parallel groupings:
Sites 1–5: located along the same line as the rift system (ridge axis continuation)
Sites 6–10: located slightly to the east, marking the adjacent sites of the same convection structure
This arrangement suggests a relationship between deep mantle flow, rift geometry, and surface permeability.
Sites Along the Rift-Aligned Division Line (1–5)
These sites are found along a line that can be calculated by extrapolating the main structure of the Reykjanes Ridge.
1. Blue Lagoon
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The Blue Lagoon is located directly within the Reykjanes rift system. It sits on the inferred convection roll, but more specifically at the intersection with a division line perpendicular to the roll.
This is significant:
The heat source reflects deep upwelling along the ridge-parallel structure
The surface expression is controlled by fractures oriented across that structure
It demonstrates how geothermal systems depend on both mantle heat supply and crustal pathways.
2. Deildartunguhver / Krauma
This area represents one of the strongest geothermal outputs in Iceland.
Deildartunguhver is a major source of hot water
Krauma utilizes this heat for bathing
Its position suggests a direct connection to the main upwelling zone, where heat is transferred efficiently from depth.
3. Skógaböðin
Located near Akureyri, this site taps geothermal water from depth.
The water source appeared unexpectedly during the excavation of a tunnel through a nearby mountain—an observation that fits well with the idea of a linear geothermal corridor aligned with the ridge.
4. GeoSea
GeoSea represents a coastal manifestation of geothermal flow.
Hot water flows from the mountain and mixes with seawater, showing how geothermal systems can extend laterally from the division line between mantle convection rolls.
5. Skógalón í Öxarfirði
This remote site is less well known but important.
Its position suggests it may trace the northern continuation of the same division line.
Sites Along the Eastern Parallel Division Line (6–10)
These sites lie 1.5° east of the main division line of the Reykjanes Ridge, reflecting a parallel effect of the same convection roll, combined with the additional effect of perpendicular lines.
6. Reykjadalur (and nearby lagoon being constructed)
Reykjadalur is a clear example of active hydrothermal circulation.
It lies along a fracture-controlled area, likely aligned with a division line perpendicular to the main convection roll.
7. Laugarvatn Fontana
This site had a natural steam bath for a long time, but has now been developed further into a spa called Fontana.
It is on the parallel line, not being assisted by any perpendicular line.
8. Geysir
Although not developed as a bathing site, Geysir could function as one.
It is particularly important because:
It sits within a well-defined geothermal area.
It is associated with a perpendicular line, slightly east of the main Reykjanes Ridge convvection roll.
This reinforces the idea that geothermal sites often occurs at structural intersections.
9. Hveravellir
Hveravellir lies in the central highlands and is key to the overall pattern.
It effectively links southern and northern geothermal sites, supporting the idea of a continuous structure.
10. Mývatn Nature Baths
This site lies within one of Iceland’s most active volcanic systems, that of Krafla.
It represents a major hub of geothermal activity.
Overall Interpretation
This arrangement suggests:
A primary convection rolls division line aligned with the Reykjanes rift
A secondary row of geothermal sites 1.5° to the east
Frequent control by perpendicular divisions of other layers
The most important takeaway is:
Geothermal sites are not simply located above heat sources—they occur where heat, and permeability intersect, often at intersecting structures.
All the sites, except Laugarvatn, illustrate this especially well, as they appear linked not only to the onvection structure but also to cross-cutting, perpenidculary aligned, division lines.
Tectonic drift is measured quite accurately, and the relevant main division line through Iceland is marked here.
The division between the North American and Eurasian plates in Iceland has a chain of geologically significant landmarks. These sites, when viewed together, outline the structure of the plate boundary and reveal a coherent tectonic pattern that aligns with large-scale mantle flow processes.
1. Njörður volcanic site (offshore)
To the west, the system begins offshore at the Njörður volcanic site, an area characterized by frequent earthquakes. This location acts as a shifting point in the tectonic framework. South of it lies the typical structure of the Mid-Atlantic Ridge, which can be traced according to a regular geometric pattern as it extends southwestward. At Njörður, however, the ridge bends more sharply toward Iceland, marking a transition from a classic mid-ocean ridge into a more complex on-land system with volcanic systems, grouped into volcanic zones.
2. Reykjanes Peninsula – Bridge Between Continents
Bridge between continents
The next key landmark is the Bridge Between Continents, a man-made structure that directly reflects geological reality. It sits at the northern edge of a rift valley and marks the visible boundary between the plates. Interestingly, the bridge itself is located on the North American Plate, illustrating how the plate boundary is not a single line but a zone of deformation.
3. Svartsengi / Blue Lagoon volcanic system
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In this region, magma actively ascends from depth, accumulating in a shallow magma chamber beneath the Blue Lagoon. From there, it propagates into dikes aligned southwest–northeast, consistent with the regional stress field. These intrusions periodically reach the surface, producing fissure eruptions characteristic of the Reykjanes volcanic zones.
4. Þríhnúkahellir and Bláfjöll
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Further inland lies the volcanic area of Þríhnúkahellir and Bláfjöll. This region provides rare access to the interior of a magma chamber and represents a structurally distinct volcanic system within the broader plate boundary zone.
5. Hveragerði
The town of Hveragerði, often called the “hot spring town” or “flower town,” sits directly within a geothermal field. Its numerous hot springs and greenhouse agriculture reflect high heat flow and shallow geothermal activity.
6. South Iceland Seismic Zone
Between Hveragerði and Hekla lies the South Iceland Seismic Zone, a region of intense seismic activity. This transform-like zone accommodates lateral motion between segments of the plate boundary and is clearly detectable through geophysical measurements.
7. Hekla
Hekla is one of Iceland’s most famous volcanoes. Its frequent eruptions and mixed eruptive style make it a key marker within this tectonic alignment.
8. Landmannalaugar
The geothermal area of Landmannalaugar is known for its rhyolitic formations, hot springs, and complex volcanic history, representing a more evolved magmatic system.
9. Laki (Lakagígar)
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The Laki fissure system produced the devastating 1783 eruption, one of the largest lava outpourings in recorded history, with profound climatic and societal impacts.
10. Grímsvötn
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Grímsvötn is a powerful subglacial volcanic and geothermal system beneath Vatnajökull, known for frequent eruptions and strong geothermal activity.
11. Kverkfjöll
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At Kverkfjöll, geothermal heat interacts directly with glacial ice, forming a complex volcanic environment. Within your framework, this site fits particularly well into the broader convection-roll pattern.
12. Askja
The Askja caldera lies near the central axis of the North Volcanic Zone. It represents a major կենտրոն point in the tectonic and magmatic system.
13. Krafla
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The Krafla volcanic system sits within a structurally complex region, where multiple smaller tectonic segments intersect, forming what can be interpreted as a hub within the larger pattern.
14. Öxarfjörður
Finally, at Öxarfjörður, geothermal activity reaches the coastline. This marks the northern continuation of the system and again aligns with the broader structural framework.
Magic Magma 