Magic Magma

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.

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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.

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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

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Iceland’s Seven Geothermal Power Stations

May 11, 2026 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

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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To Clarify: Mantle Convection Rolls and the Geological Framework of Iceland

May 11, 2026 Steingrimur Thorbjarnarson

Here is a good way to take a first look at how the mantle convection-roll system beneath Iceland works:

The convection rolls, once incorporated into a model of Iceland and the layers below it, appear to explain much of the country’s main geological framework. It is easiest to begin with the uppermost layers, since they likely have the most direct influence on the tectonic plate above. Here, a section is shown with reference points A and B. We can then focus on four distinct convection-roll sections.

The first roll, extending from the Kolbeinsey Ridge, corresponds closely with the West Volcanic Zone and the Reykjanes Volcanic Zone, eventually meeting the Reykjanes Ridge system of rolls at the southwestern corner of the country.

The second roll passes beneath the northern part of the North Volcanic Zone and extends toward the center of Iceland, framing the Central Volcanic Zone. It also aligns well with the South Iceland Seismic Zone.

The third convection roll is situated beneath the complex formed by the southern part of the North Volcanic Zone, the East Volcanic Zone, the South Iceland Volcanic Belt, and the Westman Islands volcanic system.

The fourth roll, located near point B, appears to provide the conditions necessary for the Öræfajökull Volcanic Belt.

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The Geologically N-American Part of Iceland

May 10, 2026 Steingrimur Thorbjarnarson

The tectonically N-American part of Iceland. Different aspects of seismic and volcanic activity explained.

The volcanic activity of Iceland can be examined by emphasizing the role of the North American side of the plate boundary system. In general, the North American Plate lies west of the mid-ocean ridges, the Kolbeinsey Ridge north of Iceland and the Reykjanes Ridge south of it. Iceland, however, is different, because two regions appear to transfer the volcanic activity eastwards. This is commonly explained simply by referring to a mantle hotspot beneath Vatnajökull, but here the process is interpreted somewhat differently.

According to this interpretation, convection rolls in the mantle layers beneath the tectonic plate contain both upwelling and downwelling sides. At the latitude of Iceland, the volcanic activity shifts eastwards from one side of the convection rolls to the other. Instead of forming a simple linear ridge, volcanic zones develop because the convection-roll structure interacts with the tectonic forces associated with the overall westward drift of the North American Plate. This interaction results in a broader rifting process and the formation of distinct volcanic and seismic zones across Iceland.

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The Symmetry of the Equatorial Mid-Atlantic Ridge

May 9, 2026May 9, 2026 Steingrimur Thorbjarnarson

The equatorial symmetry of the Mid-Atlantic Ridge

What is special about the equatorial section of the Mid-Atlantic Ridge? This segment extends across roughly one third of the distance between South America and Africa along the equator — approximately 20° of longitude within the roughly 60°-wide Atlantic Ocean at equatorial latitudes. The geometrical midpoint of the Atlantic at the equator therefore lies near 21°W, with about 30° extending westward to the coast of South America near 51°W and about 30° eastward to the African coast near 9°E.

When examining the zigzag geometry of this section of the Mid-Atlantic Ridge, an additional symmetry appears. The major deviations toward more northerly and southerly alignments occur at approximately equal distances from this central point, around 9° to either side. If one considers a basic upper-mantle convection-roll width of roughly 1.5°, together with a broader large-scale equatorial spacing pattern of about 30°, the geometry becomes particularly intriguing.

Naturally, this section of the Mid-Atlantic Ridge has been studied extensively using the full range of modern marine geophysical methods. The individual segments and fracture zones are well mapped and documented. Two of the most prominent equatorial fracture zones are the St. Paul Fracture Zone and the Romanche Fracture Zone, which together form a striking en-echelon pattern along the equatorial Atlantic.

To realize the importance of the equator, the most basic map of convection rolls division lines can be added: