Tag: science

Uncategorized

Iceland’s Seven Geothermal Power Stations

Steingrimur Thorbjarnarson

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.

Uncategorized

Two outposts of the Ring of Fire: Yellowstone and Changbai

Steingrimur Thorbjarnarson

At first glance, the Yellowstone hotspot and the Changbai Mountains seem to lie far outside the familiar boundaries of the Ring of Fire. They are usually treated as exceptions, features belonging to entirely different systems. But what if they are not exceptions at all? What if they are clues? See: https://www.youtube.com/watch?v=3C2HVOB-g5s

Ring of Fire – geometrical shape with Changbai Volcano and Yellowtone Caldera pointed out.

A geometrical starting point

Trying to define a strict geometrical shape for the Ring of Fire may seem futile. Still, it is worth attempting, not as a final answer, but as a way of revealing structure. A useful starting point is to consider two major anchor regions roughly 150° apart along the equator: the subduction zones along Indonesia and those along the west coast of South America. These are not arbitrary points; they represent fundamental expressions of how the Pacific Plate interacts with its surroundings.

From here, an elliptical form can be traced around the Pacific basin. It is basically a perfect ellipse. The Earth is rotating, and the Coriolis effect acts in opposite directions in the two hemispheres. The result is a systematic distortion: the structure is skewed westward in the Northern Hemisphere and eastward in the Southern Hemisphere.

Why the Ring is not a ring

This distortion helps explain something that has long puzzled geologists: the Ring of Fire is not actually a closed ring. It resembles a horseshoe.

One key reason lies in the western Pacific. Subduction zones there, particularly the Tonga–Kermadec system, do not simply trace the outer boundary. Instead, they appear within it, as if mirrored inward. This is consistent with a rotating system where structures are not just arranged spatially, but dynamically shaped. The “ring” is therefore not a rigid boundary. It is the visible expression of a deeper, moving system.

Extending the pattern

If this geometrical framework has any validity, it should not stop neatly at the edges of the Pacific. And indeed, it does not. Volcanic regions in Antarctica can be fitted into the same broad pattern. This alone suggests that we are not dealing with a local phenomenon, but with something that reflects global-scale mantle behavior. And this is where the two outposts come back into focus.

Rethinking Changbai

The Changbai Mountains have long been considered outside the Ring of Fire. Yet seismic evidence shows that material from the Pacific Plate has descended into the mantle transition zone (410–660 km depth) and then spread laterally beneath northeastern Asia. In other words, the influence of Pacific subduction does not stop at the trench. It continues far beneath the surface, so therefore Changbai is not disconnected. It is linked, but in a way that is not immediately visible from above.

Yellowstone as a counterpart

On the opposite side, Yellowstone sits deep within the North American continent. It is typically explained as a mantle plume, rising independently from great depth. But its position relative to the broader geometry is striking. If we extend the distorted elliptical framework, Yellowstone lies close to its outer margin, mirroring Changbai on the other side of the Pacific system.

Beyond the outline

So what lies behind the geometry? The Ring of Fire, when viewed not as a boundary but as a pattern, appears to outline something larger: a system of long, connected mantle flows encircling the Pacific. Subduction zones are only the surface expression of this system. The deeper structure may extend far beyond them, both laterally and vertically.

In that context, Yellowstone and Changbai are not anomalies. They are signals. They suggest that the system does not end at the edges we draw on maps. It continues beneath them. And that may be where the real structure lies.

Uncategorized

The division line of the West Volcanic Zone of Iceland

Steingrimur Thorbjarnarson

By examining a relief map of Iceland, key geological features become far more apparent than they would otherwise. One such map is displayed in the lobby of the visitor center at Þingvellir.

The main division line of West Volcanic Zone and its surroundings

A broken red line has been drawn to delineate the boundary along the western margin of the Western Volcanic Zone. This boundary can be traced continuously from north to south across the landscape. At its northernmost extent lie Hveravellir, a significant high-temperature geothermal field situated in the central highlands. Immediately to the west is Langjökull, beneath which two volcanic systems are located. Proceeding southward, one encounters Hvítárvatn, a proglacial lake that serves as a major outlet for meltwater from Langjökull and lies directly on this geological boundary.

Further south, the Jarlhettur form a row of hyaloclastite ridges aligned along the same divisional trend. This boundary corresponds to the interface between two mantle convection rolls beneath the approximately 120 km thick lithospheric plate. In addition to this division, deeper convection rolls boundaries are present, above which lies the Geysir geothermal area.

South of this part, volcanic formations of a different character emerge, including Laugarvatnsfjall, located above the lake Laugarvatn, pointed out on the map. These formations extend westward to Kálfstindar at the side of the Þingvellir graben, which follows the same orientation as the main boundary shown here. The geothermal activity at Laugarvatn is well documented. Immediately south of Laugarvatn lies the shield volcano Lyngdalsheiði. The boundary intersects the summit crater Þrasaborgir.

Notably, the hydroelectric power stations along the Sog river are situated on this boundary, marking a transition from highland terrain to the west to lower elevations in the east. The former waterfall Ljósafoss was located precisely along this division. Further south lies the mountainous region associated with Hrómundartindur, of which Reykjafell, near Hveragerði, forms a part. Here, deeper boundaries between mantle convection rolls extend westward beneath the Hengill volcanic system. South of this area, sharply defined structural boundaries known as Hlíð appear. These correspond in practice to the eastern flank of the shield volcano Skálafell and associated volcanic formations along the eastern edge of the Western Volcanic Zone.

In this region, the mantle convection rolls rotate in opposite directions. The western side coincides with the West Volcanic Zone, where one convection roll resists the northwestward motion of the North American Plate. In contrast, the area to the east is transported along with the underlying mantle flow. Consequently, the western region is subjected to continuous extensional forces, resulting in crustal rifting. This process is most clearly expressed in the rift valley at Þingvellir.

Uncategorized

Mapping Volcanoes to Mantle Flow in the Aegean Sea

Steingrimur Thorbjarnarson

The South Aegean Volcanic Arc, including Santorini, is one of the most active and famous volcanic regions of the Mediterranean. It formed mainly through subduction of the African Plate beneath the Aegean/Eurasian region along the Hellenic subduction zone. The arc includes, from west to east, the volcanic fields of Sousaki–Aegina–Methana–Poros; Milos; Christiana–Santorini–Kolumbo; and Kos–Nisyros–Yali/Gyali.

In the convection-roll model, the arc is highly symmetrical around the central axis of the Aegean Sea, and the model as well, while still being affected by the westward tectonic drift of the Anatolian region. The volcanoes appear to fall along specific modeled convection-roll lines. This close fit between a mathematical model and observed surface volcanism adds statistical support to the relevance of the model.

The volcanic alignment can be summarized as follows:

Sousaki, Aegina, Methana, and Poros are situated above the westernmost set 1.
Milos lies above the second set of downwelling lines.
Central Axis: Santorini and Kolumbo are located near the central axis of the Aegean Sea.
Nisyros, Gyali (Yali), and Kos are positioned above the easternmost downwelling line of set 4.

Within the South Aegean volcanic arc, four sets of lines are identified in the convection-roll model. However, volcanic centers are concentrated above only three of these. Notably, no volcanoes are observed directly above the line of the pair marked as number 3. Instead, volcanic activity, most prominently at Santorini and Kolumbo, is located between lines marked as 2 and 3, aligning closely with the central axis of the Aegean Sea.

This pattern suggests that the central axis may act as a preferential path for magma ascent. Similar axial focusing has been observed in other tectonic settings, such as Iceland (particularly the North Volcanic Zone), where mantle upwelling and crustal weaknesses combine to localize volcanism and high temperature areas along a central N-S aligned axis.

Within the framework of this model, it can be hypothesized that mantle material associated with line 3 does not produce surface volcanism directly above it. Instead, the flow may be laterally redistributed, potentially westward, before rising along zones of reduced lithospheric strength at the central axis. This would imply that the interaction between convection patterns and lithospheric structure plays a key role in determining the final location of volcanic activity.

This suggests that the division lines of the convection rolls play a decisive role in determining the exact locations of volcanic activity. The activity itself is, of course, initiated by the subduction of the African Plate and the associated processes. As in many other regions of the world, subduction creates a volcanic arc that is clearly detectable at the surface and is dotted with volcanoes. It is precisely at the points where the convection-roll division lines intersect this arc that volcanic centers appear.

In this context, the blue downwelling lines may also be interpreted as marking conduits for ascending magma. The term “downwelling” refers to the slow convection of plastic mantle material; however, along the boundaries between convection rolls, at the division lines, partial melting can occur. This process may create zones of weakness within the lithosphere, providing favorable conditions for magma ascent and, ultimately, volcanic activity at the surface.

Uncategorized

What We Learn from Ophiolites

Steingrimur Thorbjarnarson

Ophiolites are slices of oceanic crust that have been uplifted and exposed, making it possible to examine a cross-section of a tectonic plate. This provides a valuable opportunity to study the different layers of the Earth. There are many ophiolites, the most famous probably being those found in Oman and Cyprus. These were emplaced onto continental crust through obduction and are in some cases tilted or rotated.

After: http://www.gulfpetrolink.com/geoarabia/index.php/ga/article/view/31997

The uppermost ~5 kilometers of the brittle oceanic crust can thus be examined in cross-section. At the top lies a layer of pillow lavas, beneath which are sheeted dikes, followed by a gabbro layer extending down to the Moho discontinuity. In favorable cases, ophiolites also expose portions of the underlying mantle.

At the Moho, there is typically a transition zone composed mainly of two rock types: wehrlite just below the gabbro, followed by dunite. Beneath this lies the lithospheric mantle, which is composed mainly of harzburgite. This is a type of peridotite that remains after the original lherzolite of the asthenosphere has undergone partial melting to produce basalt.

Basalt originates from the asthenosphere at depths of around 120 km. The temperature of basalt at eruption at the Earth’s surface is surprisingly close to the temperature at which it originally formed. In Iceland, basalt may represent up to about 20% partial melting of the original lherzolite.

One particularly important feature revealed by the exposure of mantle below the Moho is the presence of conduits through which partial melt (basaltic magma) has traveled. These conduits consist of dunite, composed almost entirely of olivine. They form vertical channels leading up toward the Moho. This indicates that partially molten material can flow upward relatively rapidly, entering the gabbroic section immediately above the Moho transition zone.

The gabbro zone is commonly divided into two parts, with the lower portion showing layered structures. Within this zone, basaltic magma can accumulate in sills and magma chambers, where it may partially crystallize before continuing its ascent. When conditions allow, the magma rises again, typically vertically, through the sheeted dike complex, forming successive dikes.

As frequently observed in Iceland, such processes can eventually lead to volcanic eruptions at the surface. On the ocean floor, these eruptions typically produce pillow lavas. The vertical continuity and rather fast flow of basalt up through the tectonic plate can explain how it maintains temperature (almost) found at the depth of 120 km at the surface. This AI picture expresses the process:

AI-version of the ascending path of magma – not to scale.

The vertical movement of partially melted material through the tectonic plates can partly explain why division lines in the asthenosphere can be detected at the surface. This process continues over long distances, forming dikes of considerable length. Even more importantly, this ongoing process creates divisions around which different parts, often described here as polygons, can adjust to the tectonic drift that constantly alters the positions of continents and oceanic crust. Another contributing factor is the local horizontal movement, combined with the global tectonic drift trend, which can lead to localized rifting or pressure at the surface.

For mainland crust, the section looks slightly different for the upper most part. Again, this AI image can be made:

AI-generated cross-section of a continental plate – not to scale.

The result of this activity, which can be traced in mantle remains of ophiolites, can be detected on the surface. This is the map of Iceland: