Tag: iceland

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Iceland’s Seven Geothermal Power Stations

Steingrimur Thorbjarnarson
The seven geothermal power stations currently producing electricity in Iceland

Iceland is unique among nations because nearly all of its geothermal power production is located directly within an active plate boundary zone. The country stands astride the northern section of the Mid-Atlantic Ridge, where the North American Plate and Eurasian Plate slowly drift apart.

Within this environment, geothermal activity is not isolated. Instead, it forms part of a large interconnected tectonic and volcanic framework extending from the Reykjanes Ridge in the south to the volcanic systems of northeast Iceland.

The seven geothermal power stations producing electricity in Iceland are therefore much more than industrial facilities. Together they outline the geometry of the active volcanic belts of Iceland itself.

The Hengill Geothermal Complex

The largest concentration of geothermal power production in Iceland is found at Hengill, one of the most active volcanic systems in southwest Iceland.

Hellisheiði Power Station

Hellisheiði Power Plant

Located on the southern side of the Hengill volcanic system, Hellisheiði Power Station is the largest geothermal power station in Iceland. It produces both electricity and hot water for the Reykjavík metropolitan area. Steam rises from wells drilled deep into fractured volcanic rocks directly above the active rift zone.

However, it is noticeable that Hellisheiði Power Station is not situated exactly above the tectonic division line between the plates, but slightly offset along the mantle convection rolls division lines interpreted in the area. These red upwelling lines, associated with the second and fourth convective layers, being rather evenly distributed between approximately 120 and 670 km below Earth’s surface,  form the boundary between the Reykjanes Oblique Rift Zone and the West Volcanic Zone.

In this respect, the location of Hellisheiði resembles that of Svartsengi Power Station, as both are positioned along opposite sides of the same convection-roll framework.

Nesjavellir Geothermal Power Station

Situated near Þingvallavatn, Nesjavellir Geothermal Power Station occupies another section of the same tectonic environment. Together, Hellisheiði and Nesjavellir form the largest continuous geothermal utilization area in Europe. The two power stations largely make use of the same geothermal resources associated with the Hengill Volcanic System.

The location is highly significant geologically. The Hengill region lies exactly where volcanic activity, tectonic spreading, and large-scale fracture systems intersect.

Reykjanes Peninsula — Directly Above the Plate Boundary

The geothermal stations on the Reykjanes Peninsula are perhaps the clearest examples in the world of energy production directly tied to an exposed oceanic rift zone on land.

Svartsengi Power Station

Svartsengi Power Station became internationally known because of the nearby Blue Lagoon. However, geologically it is equally fascinating. The station extracts geothermal fluids from highly permeable volcanic formations created by repeated rifting episodes.

The intersections between the tectonic division line of Iceland and the interpreted convection-roll division lines are particularly apparent in this area.

Reykjanes Power Station

At the southwestern tip of Iceland, Reykjanes Power Station operates in one of the most tectonically active environments in the North Atlantic. Here, geothermal reservoirs are strongly influenced by seawater interaction and high-temperature magmatic systems beneath the peninsula.

The recent volcanic activity on Reykjanes has demonstrated how dynamic this part of Iceland remains.

Northeast Iceland — Rift Volcanism and High Heat Flow

The northeastern volcanic zone contains another cluster of geothermal power production associated with active crustal spreading.

Krafla Power Station

Krafla Power Station stands within one of Iceland’s most famous volcanic systems. The eruptions and rifting events of 1975–1984 transformed scientific understanding of how magma intrusions accompany plate spreading. A central hub, where several interpreted convection-roll division lines intersect within a comparatively small area, coincides with the geothermal activity associated with Krafla, Bjarnarflag Power Station, and Þeistareykir Power Station.

All of these three power stations are located slightly west of the tectonic division line, in apparent association with the mantle convection-roll division lines.

Bjarnarflag Power Station

Located near Mývatn, Bjarnarflag was one of Iceland’s earliest geothermal power stations. Though relatively small, it occupies an extremely important geological setting along the active rift.

Þeistareykir Power Station

Þeistareykir is one of Iceland’s newest geothermal developments. The area had long been known for extensive geothermal manifestations, but only in recent years has large-scale utilization become possible.

A Geological Pattern

What makes these seven power stations especially interesting is their apparent relationship both to the tectonic division line between the North American and Eurasian plates and to the interpreted divisions between the modeled mantle convection rolls mapped here. They are not randomly distributed across the country. Reykjanes Power Station and Svartsengi Power Station are found at the western end of the Reykjanes Peninsula, closely associated with the plate boundary zone itself.

In addition, Svartsengi appears to coincide with two downwelling lines associated with the second and fourth convective mantle layers. As mentioned before, these four modeled layers are interpreted as being rather evenly distributed between approximately 120 and 670 km below Earth’s surface.In many ways, the geothermal power stations themselves appear to reflect the tectonic framework of Iceland.

The pattern also illustrates a broader geological principle: geothermal energy is fundamentally linked to large-scale heat transport within Earth’s crust and upper mantle. Iceland simply exposes this relationship more clearly than almost anywhere else on Earth. For that reason, Iceland remains one of the world’s most remarkable natural laboratories for studying mantle processes, crustal spreading, volcanism, and geothermal systems.

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Six Geological Chapters Along Iceland’s Most Popular Tourist Route

Steingrimur Thorbjarnarson
The six “chapters” of the tourist route through South Iceland

For the first chapter marked on the map, you visit Þingvellir National Park. In order to get there, you pass through the highland structure of the West Volcanic Zone, and at its central axis you find the rift valley of Þingvellir. You then drive all the way to Laugarvatn, where abundant geothermal activity is found along the boundary of polygon 2. From there, you turn north until you reach the Geysir area and Gullfoss at the northern end.

If you wish to continue to other scenic areas in the south, you can follow the main road running parallel to the boundary between polygons 1 and 2 until you reach the Ring Road, where you make a 90° turn toward the southeast. The road remains fairly straight until it crosses the boundary between polygons 2 and 3. After that, it curves around the two glaciers Eyjafjallajökull and Mýrdalsjökull.

Polygon 3 is centered around Eyjafjallajökull and includes two famous waterfalls: Seljalandsfoss at its western end and Skógafoss on its southern slopes. After passing the town of Vík í Mýrdal, at the southernmost point of Iceland, you enter chapter 4.

There, you pass two enormous lava fields, the largest on Earth formed in recorded history, one from the Eldgjá eruption of 939 and the other from the Laki eruption of 1783. There are two parallel roads there, and you would probably choose the northern one (road No. 1), but I chose the southern one for illistration 🙂 At the boundary between polygons 4 and 5, another turn is made to the right, crossing that polygon and passing the glacial rivers flowing from Vatnajökull. This area is generally known as Skeiðarársandur.

Upon reaching the end of polygon 5, you drive around Öræfajökull, the largest volcano in Iceland. Entering polygon 6, you are on the road toward the Glacier Lagoon, Jökulsárlón. You can then continue along the road running parallel to the side of the polygon all the way to the eastern end.

If you notice other roads that fit this pattern in a similar way, convection rolls underneath affecting the road system, it would be very interesting to examine them as well.

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Understanding the Geothermal Areas in the North of Iceland

Steingrimur Thorbjarnarson

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.

The study area
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The 1.5° Spatial Sequence of Iceland

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.

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.

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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.

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.