Tag: geology

Uncategorized

The Central Role of Hekla Volcano

Steingrimur Thorbjarnarson

Hekla is known to occupy a uniquely important geological position within Iceland. It lies at the eastern end of the South Iceland Seismic Zone (SISZ) and simultaneously forms the southwestern gateway into the East Volcanic Zone (EVZ). In many ways, Hekla stands at the transition between two fundamentally different tectonic expressions: the transform-style seismic deformation of South Iceland and the broad volcanic rifting of the eastern volcanic systems.

The rifting process commonly described in Icelandic geology, where one side of Iceland drifts roughly 1 cm westward each year while the other moves about 1 cm eastward, can be visualized as being organized around a central tectonic division line that reaches the latitude and structural position of Hekla. This gives Hekla a particularly important geometric and tectonic role within the overall framework of Iceland.

The East Volcanic Zone is more difficult to represent with a single line than the oceanic ridges north and south of Iceland, because the EVZ is not a narrow ridge crest but rather a broad tectono-volcanic corridor 1.5° wide from east to west. In this interpretation, special emphasis is placed on the eastern boundary of the EVZ, which appears to function as a major division between tectonic domains associated with the North American and Eurasian plates. Rather than viewing the EVZ simply as a diffuse volcanic belt, it can therefore be examined as a structured rift system occupying a broad zone between deeper mantle flow divisions.

When zooming out to examine the large-scale geometry of Iceland itself, including the mid-ocean ridges and the surrounding continental shelf, an even more remarkable arrangement becomes visible, with Hekla occupying a central position within the overall symmetry.

Location of Hekla (red circle) and the Elliptical Outline of the Continental Shelf of Iceland.

The continental shelf surrounding Iceland has a surprisingly regular form. The southeastern quarter of the shelf, in particular, remains relatively undisturbed and displays a sharp elliptical geometry that can be detected mathematically. The ellipse possesses clearly identifiable major and minor axes aligned directly east–west and north–south respectively. Significantly, Hekla is located on the north–south minor axis of this elliptical structure.

If the major and minor axes of the Icelandic shelf ellipse are drawn, and the oceanic segments of the Reykjanes Ridge and Kolbeinsey Ridge are extended toward Iceland from the south and north, the two ridge extensions converge precisely in the central point of the ellipse itself (extrapolation shown with dotted lines). This creates a striking geometric relationship between:

  • the elliptical form of the Icelandic continental shelf,
  • the mid-ocean ridge system north and south of Iceland,
  • the tectonic division between the North American and Eurasian plates,
  • and the position of Hekla within the overall structure.
https://images.openai.com/static-rsc-4/f0-26YLRxhCiJe-Z8uX1Q2B7ceulF2OD7H-1f2yVrPH5odNHbqA4tI9Z60AV0DdbyQbG7U0xvQZqy8F5o3SFFts3s8l2aDaW7zROriGXKW_8bQwV4MMAjj4BZzGOvQavqSl9XDhOBwfYs9x2TPJwF0-AMJY-NMqUhZ_rI9iOXk9R2U2qgLRgWCi-sHkWsqZT?purpose=fullsize

The tectonic division line through Iceland also appears remarkably symmetrical when compared with both the elliptical outline of the shelf and the extended ridge axes. North and south of Iceland alike, the plate division lines merge naturally into the mid-ocean ridges exactly where those ridges intersect the elliptical margins of the shelf.

Within this broader framework, the detailed geometry of mantle convection-roll polygons and their division lines becomes increasingly important. The interaction between different mantle layers, tectonic boundaries, volcanic zones, and continental-shelf geometry may together help explain why Hekla occupies such an exceptional position within Icelandic geology.

Location of Hekla.

Hekla has been regarded as Iceland’s most famous volcano for centuries, and perhaps not only because of its frequent eruptions and dramatic appearance. Its location suggests that it occupies one of the most structurally significant positions in the entire geological framework of Iceland.

Hekla
Uncategorized

The Three Corners of Vatnajökull

Steingrimur Thorbjarnarson

The largest glacier in Iceland, Vatnajökull, covers several major volcanic systems. Direct geological research beneath the glacier is difficult because of the extreme environmental conditions, thick ice cover, and active geothermal areas. Nevertheless, a remarkable amount is known about the volcanic framework beneath the ice.

Vatnajökull with Öræfajökull, Grímsvötn and Kverkfjöll.

Three prominent volcanic regions are especially important in this context because they appear to fit clearly into the proposed pattern of mantle convection roll division lines.

The first is Öræfajökull, the tallest volcano in Iceland, situated close to the 64th parallel. The second is Grímsvötn, a vast but more obscure volcanic and geothermal complex beneath central Vatnajökull. The third is Kverkfjöll, which occupies a relatively small polygon directly north of Öræfajökull.

Kverkfjöll is particularly significant because it marks the southern starting point of the North Volcanic Zone. From there, a remarkably direct volcanic axis can be traced northward all the way to Öxarfjörður, where the North Volcanic Zone meets the Tjörnes Fracture Zone. This fracture zone, in turn, connects the volcanic systems of Iceland with the offshore Kolbeinsey Ridge.

The geometrical relationship between these three volcanic centers is striking. The polygon formed by Öræfajökull, Grímsvötn, and Kverkfjöll appears exceptionally clear within the proposed convection-roll framework. In addition, Grímsvötn and Kverkfjöll are known to be petrologically related, suggesting a deeper structural connection beneath Vatnajökull.

Grímsvötn was also the source region of the magma and dyke propagation that eventually produced the catastrophic Laki eruption in 1783. Within this framework, the magma migration becomes especially interesting because the dyke propagated from one calculated division line toward another before the eruption began. Laki itself lies on one division line, whereas Grímsvötn occupies another.

The line extending from Kverkfjöll through Grímsvötn to Laki closely coincides with the eastern boundary of the East Volcanic Zone. The width of this volcanic zone can be measured directly on the surface, and it corresponds closely to the calculated width of the relevant convection roll in the model.

On the opposite side of the Grímsvötn–Kverkfjöll line lies Öræfajökull, which also marks the beginning of another volcanic alignment: the Öræfajökull Flank Zone. This zone trends northeast–southwest and extends toward Snæfell northeast of Vatnajökull. In total, the flank zone spans approximately the equivalent of two polygons within the proposed geometrical framework.

The repeated appearance of the same fundamental geometrical unit — polygons with an approximate east–west width of 1.5° — is one of the main reasons the model may provide a valuable tool for examining geological structures. According to this interpretation, the same geometrical relationships are not confined to Iceland alone, but may also appear in tectonic and volcanic systems throughout the world.

Geothermal areas of Iceland with superimposed mantle convection roll division lines and the tectonic boundary between the North American and Eurasian plates.

Within Iceland, however, Vatnajökull provides one of the clearest large-scale examples. Beneath the ice cap, some of the country’s most powerful volcanic systems appear organized in a pattern that mirrors the calculated geometry of the mantle convection roll model. Each polygon therefore becomes something like a chapter in a book, with each one containing its own distinct geological characteristics, tectonic structures, volcanic systems, geothermal activity, and landscape evolution.

Viewed in this way, Iceland can be examined as a sequence of interconnected geological “chapters,” where every polygon reveals a slightly different expression of the same underlying mantle convection roll system. One polygon may be dominated by rifting and fissure swarms, another by central volcanoes and geothermal fields, while a third may display transform faulting, glacial volcanoes, or complex magma interactions beneath ice caps.

This approach is valuable because it provides a structured way to examine geology step by step. Instead of viewing Icelandic geology as a collection of isolated volcanic systems, each region can be interpreted as part of a larger geometrical framework extending through the crust and into the mantle below.

The same method can also be applied to other parts of Iceland. The Reykjanes Peninsula, the South Iceland Seismic Zone, the Hengill area, the central highlands, and the northern volcanic systems all become individual “chapters” whose geological behaviour can be compared within the same overall framework.

In that sense, the polygon system is not only a geometrical model. It also becomes an organizational tool for understanding geology across many different scales — from magma migration beneath a glacier to the overall tectonic structure of Iceland itself.

Uncategorized

Comparing the three equatorial landmasses of South America, Africa, and Indonesia

Steingrimur Thorbjarnarson
Comparing the Equatorial Landmasses

Comparing the three equatorial landmasses of South America, Africa, and Indonesia, we should consider the geometry of these regions and the geological features that immediately stand out on a global map.

Starting with South America, the enormous Peru–Chile Trench forms the westernmost tectonic boundary of the continent. To the north lies the Caribbean region, partly encircled by another major subduction system. The easternmost point of this equatorial landmass is represented by the Amazon Estuary. The next diamond-shaped equatorial landmass, Africa, is located roughly 60° farther east. Its western margin lies along the Atlantic coast of Africa, while its eastern corner corresponds to the region of the Great Rift Valley, one of the most tectonically active continental structures on Earth. Looking farther east toward Indonesia, the western boundary lies near Sumatra, close to the site of the enormous eruption about 74,000 years ago, commonly associated with the largest caldera in the world of Lake Toba, which some researchers suggest almost wiped out early human populations. The eastern margin of this equatorial region lies within what is probably the most geologically complex area in the world, where multiple tectonic plates, island arcs, microcontinents, and subduction systems interact.

This regularity, both in the geometry of the landmasses and in the distribution of major geological structures, is intriguing. It corresponds remarkably well with the pattern predicted by modeled mantle convection rolls, based on laboratory studies showing that mantle material naturally tends to organize into elongated convection structures under conditions that can logically be expected within Earth’s interior.

From the perspective of the scientific method, this represents a prediction-and-observation type of correspondence. The large-scale surface geometry and tectonic structures visible on world maps are objective features that can be examined directly. The additional step taken here is to propose an explanation for why this pattern may have emerged. Laboratory experiments, the known layered structure of Earth, and mapped geological surface features can, in this interpretation, be viewed as parts of a single coherent framework. Within that framework, Iceland also fits naturally into the larger pattern, positioned between the equatorial regions of South America and Africa along the Mid-Atlantic Ridge. No advanced mathematics are required to recognize the broad geometric relationships visible on a world map. The spatial arrangement itself already suggests a striking degree of large-scale organization.

Hawaii, Iceland and Indonesian lines

The global pattern of the mantle convection roll system can be examined in many different ways. Focusing on the distribution of landmasses along the equator is particularly revealing, but the pattern also appears in other large-scale geological alignments. When tracing the regularity of the division lines, resembling those observed in Iceland, one can see that Hawaii is connected to the system farther west, while Indonesia aligns with the system farther east. These are observations on a planetary scale. Yet when the same framework is examined in greater detail, for example in Iceland, it also appears capable of explaining aspects of local geology.

The mantle convection rolls model is theoretical and is based primarily on seismic measurements from around the world, which reveal the layered internal structure of Earth. Nevertheless, the model becomes significant because its explanatory value extends far beyond what might initially be expected. Within this framework, the large-scale structure of the mantle can be anticipated by inserting convection rolls into the known layers of Earth’s interior. Because mantle motion is extremely slow, and no oscillation takes place, the horizontal alignment of the rolls can be calculated very accurately. In this interpretation, the geometry is controlled by convection itself, the spherical shape of Earth, and the fact that the planet rotates.

The proposed alignment of the convection rolls can then be compared with observable geological features at the surface. According to this interpretation, the boundary lines become identifiable in many locations around the world through tectonic, volcanic, geothermal, and topographic patterns. From this perspective, Iceland becomes especially important because it provides a relatively accessible surface expression of processes that may otherwise be difficult to recognize at a global scale. The combination of active rifting, volcanism, seismicity, geothermal systems, and clear tectonic boundaries allows the larger mantle framework to be examined in unusually fine detail.

Uncategorized

Indonesia’s Divide: Mantle Geometry Between Bali and Lombok

Steingrimur Thorbjarnarson

Indonesia is one of the most remarkable geological regions on Earth. Thousands of islands stretch across the equator between Asia and Australia, while some of the world’s most powerful volcanic systems rise above active subduction zones. Yet the geological structure of Indonesia is not random. Certain large-scale patterns appear repeatedly, and some of them may reflect deep convection geometry within Earth itself.

One of the clearest examples is found near the equator. The Indonesian subduction system contains major volcanic and tectonic segments spaced at surprisingly regular intervals. Particularly interesting are the great subduction arcs found 30° apart along the equatorial region. This large-scale spacing resembles geometrical organization rather than isolated local structures.

The deep channel between Bali and Lombok is not simply a surface feature. It coincides with a major tectonic and geological boundary zone. From the perspective of mantle convection geometry, this location represents a downwelling division line between adjacent convection rolls beneath the lithosphere.

https://images.openai.com/static-rsc-4/GdlPb5j_7Ogjq5KGKDyaL9h0isxZxo-Cs90XBDyUPwMHbxuAf9O1VGZMOLE7S7ahngtGIdptrdT7_qo2fCYrxXryLSddYhNtp2xDWILWAK8l9gKRlTjOzM5CxNd31yFrV36fzhJXscUj4uv-o31Xx-zTH5GvcuOo91sbEHj7MobT-czQMnEM7VClc1H0jyO5?purpose=fullsize
https://images.openai.com/static-rsc-4/gQ_LHrMi19-X9LybLDpET2fpr5xwAnpEkXv-BaTgWKbZt1uJ8N7S00xbOmPhuPRYnpaZSaaZ9p1fOq9nxI3lgFjbkQS6JlVCJboeGXN_9CcrspaS7Bfvd8qaeyll8VRlZUAxLeU7pI89bLy0AA6e4EIneDlwjMVDjf9JCWYQ-c0BnX2t4cocvJpEjWTHWXpp?purpose=fullsize
https://images.openai.com/static-rsc-4/hIbTrpCd4acRQ15NxNGTT-fY-j-sEd-gqd2U-lxbBf0uAQhNhJ0gGsh8BM6bBHVba6mcAmqesa45BJucB0ErOdCyWhDmxNBishkr5DLjHS5kDinlLrReGRyoProDv3ib5LQTaZxUe4UVKk0MDplxoTg3QOiwCHRDPKbybgkLFsvdkv0UBlK7ciB4twjc3nBA?purpose=fullsize

The Wallace Line

The naturalist Alfred Russel Wallace observed during the nineteenth century that an extraordinary biological boundary exists between Bali and Lombok.

West of the line, Asian flora and fauna dominate. Monkeys, woodpeckers, and many placental mammals are characteristic. East of the line, Australian affinities begin to appear. Cockatoos and other species linked to Australia become increasingly common farther east.

This boundary became known as the Wallace Line. What makes this especially remarkable is the geography itself. Bali and Lombok are very close together. At first sight one might expect that during Ice Age sea-level lowering the two islands would have been connected by dry land. But they never were, and the reason is that the strait between them is unusually deep. Even when sea level fell more than 100 meters during glacial periods, deep water remained between the islands. This preserved the biological separation over very long periods of time.

Deep Water and Downwelling

Division lines of the framework of the convection rolls model are of course both downwelling and upwelling. Sometimes the different effect of downwelling and upwelling becomes apparent, as downwelling zones may produce long-lived subsidence and deep marine corridors.

The Bali–Lombok Strait therefore becomes more than a biological curiosity. It may represent a surface expression of deep mantle organization.

The geometry is especially interesting because the downwelling line is parallel to a major lower-mantle upwelling division of the lower mantle (see cross section above). In this interpretation, the deep Earth structure controls not only volcanic belts, but also long-term oceanic depth patterns.

Geological Contrast Between Bali and Lombok

The difference between the two islands is therfore first and foremost to be traced to geophysics.

https://images.openai.com/static-rsc-4/eLNRzBD2E-YGQO8Te9YwUd_jy1uDa5z8EgFBTePdwBLO_Vw1P8Vt7FIuhoTZhdkypDpQxo8WwIk4O2gcQHnVfpoCsLlxp56oWV3LFLQMm4rqqk1hNLsQmHlutd4sUJJVjQOvwoGkl8C3LW0K3vF_9NtqiwLyM0MXaaRAgO0tmpfVVKCT_Wbs4th-YK2g2JlT?purpose=fullsize
https://images.openai.com/static-rsc-4/FPt3EcUtp57zB8bYGgRVl3RRZSBsd2b7kYqgoQ5wA2JcjhU4t9zMSTpErFCH_FwFt-tKk1-cx50QlbudJXCim-fHThb4e-zg38-YW5eJbDo-0qfyTGg9QUseA6BuZijsCoeksCzAUSxspmu6RNusHGlrR2ddavPdOF-gFAUTGD9YbtgfUzwHgrAbTPjW-v3F?purpose=fullsize
https://images.openai.com/static-rsc-4/L79n7OU4J8p0hCC9jS1hCY3ZWC8jtYN2NzEk80nl6xvalN8k-EmTwzKqt1d_nHvMxc_dXSWPcK8Wq2jsNWydmEjyVxtTKCuMmdQXsFqK_or_wlZ6PfdaKeaYvbJ0HHMgH4fD1qfwyH34iU_tt5wDJ7M_Md126AB-jdER59rNXBUZBsdPrJkYZ1K5aQhmso9N?purpose=fullsize

Mount Agung on Bali and Mount Rinjani on Lombok belong to the same general volcanic arc system, yet the geological environment changes noticeably eastward toward the Banda Arc transition.

Lombok also contains the remains of the gigantic 1257 eruption of Mount Samalas, one of the largest eruptions of the last two millennia.

Eastward from Lombok tectonic complexity increases, crustal deformation becomes stronger, and the Indonesian arc system begins bending toward the Banda Sea region.

Thus the Wallace Line coincides with biological change, bathymetric change, tectonic change, volcanic change, and of course mantle-flow geometry of the convection rolls model itself.

Inner Earth and Surface Evolution

The Bali–Lombok division demonstrates how deeply Earth’s internal structure may influence the surface environment. The persistent deep-water boundary prevented land bridges to form when water was trapped in large glaciers of the ice age and separated the ecosystems,

In this interpretation, the contrast between Asian and Australian realms did not arise merely from chance migration patterns or sea-level fluctuations. Instead, the geometry of mantle convection itself may have maintained the separation over geological time.

The result is one of the clearest examples on Earth where deep mantle structure, as derived from the convection rolls model, coincides with tectonics, in this case ocean depth, volcanism and biological evolution

How Wallacea, and its division, coincides with the mantle convection rolls framework.

It all appears to be interconnected within the same regional framework. https://en.wikipedia.org/wiki/Wallacea

Uncategorized

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.