Tag: iceland

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.

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

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.