Tag: science

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.

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.

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:

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:

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:

The northerly flowing rivers of northern Iceland provide an intriguing window into the deeper tectonic and geological structure of the region. North of Iceland lies the Kolbeinsey Ridge, a spreading ridge that exerts a significant influence on the country’s geology. Unlike the Reykjanes Ridge, the Kolbeinsey Ridge does not visibly intersect or “reach” the Icelandic mainland. Nevertheless, its structural imprint is evident.

The ridge exhibits a pronounced north–south (N–S) orientation, and this same directional trend can be observed across much of northern Iceland. One of the most compelling expressions of this alignment is seen in the river systems. Major rivers such as Hrútafjarðará, Héraðsvötn, Eyjafjarðará, Skjálfandafljót, Jökulsá á Fjöllum, Hofsá, and Lagarfljót largely follow northerly courses, reflecting a structural control that is unlikely to be coincidental.

In addition to their general N–S alignment, these rivers display occasional deviations that appear to coincide with subtle structural boundaries or division lines in the crust. These interruptions in flow direction may mark transitions between different tectonic domains or the influence of underlying mantle dynamics.

The estuaries of these rivers further reinforce this pattern. Their distribution shows a striking regularity that aligns with the proposed grid of convection rolls beneath Iceland. Each estuary can be interpreted as forming a “hub” within this grid, suggesting that surface hydrology may be responding to deeper, organized mantle processes. This spatial consistency lends support to the idea that convection rolls patterns influence not only volcanic and tectonic features, but also the development of drainage systems.

A careful comparison of topographic and geological maps with the river network makes these relationships more apparent. The rivers are not randomly distributed; rather, they appear to trace out an underlying structural framework. In this sense, northern Iceland’s river systems may serve as surface indicators of deeper geodynamic organization (the grid formed by mantle convection rolls), reflecting the combined influence of the Kolbeinsey Ridge and broader mantle convection patterns.

The Reykjanes Ridge is the dominant structural feature in the geology of Iceland. Its importance lies not only in its scale, but also in the way it appears to express a broader tectonic principle that influences much of the country’s geological architecture.

On the map, a red line traces the continuous (holistic) segment of the Reykjanes Ridge, extending for roughly 900 km. What is particularly notable is that this line can be described by a simple geometric relationship (of relevant degrees of latitude x and logitude y. In this case Cn = -7.66):$$(x – C_n)^2 + (y – 32)^2 = 35.34^2$$This is not merely a mathematical curiosity. In the southern half of Iceland, several major rivers and geomorphological features align closely with this same trend. Among the most prominent examples are Norðurá, Hvítá, and Þjórsá, as well as the lake Langisjór. Many additional rivers, lakes, and volcanic features follow these orientations across southern Iceland.

This alignment is not a new observation. It is widely recognized that Iceland’s rivers and tectonic features often follow consistent directional trends, and this has long been apparent to geologists and observers alike. However, what is less commonly emphasized is that this pattern can be captured, and better understood, through a specific mathematical form such as the equation above.

Seen in this light, the alignment is not just descriptive but diagnostic. It points toward an underlying organizing mechanism. The interpretation proposed here is that convection rolls beneath the lithosphere are arranged in a geometry that gives rise to this pattern at the surface.

If the Earth’s interior consisted of only a single layer of convection rolls, the resulting surface pattern would likely be much simpler and more direct. In reality, multiple layers and interacting systems of mantle flow are involved, which complicates the expression of these structures at the surface. A full treatment of these layered interactions is beyond the scope of this discussion. Nevertheless, the essential idea can be understood by focusing on one layer, which includes the pair of convection rolls shaping this section of the Reykjanes Ridge.

A useful way to visualize this is to imagine convection rolls arranged side by side, like parallel cylinders. In this framework, the Reykjanes Ridge occupies precisely a boundary between two of those rolls, and its path follows the equation given above with notable accuracy. At Iceland’s latitudes, tectonic activity becomes more diffuse. Instead of being confined to a narrow ridge, divergence is distributed across broader volcanic zones. This produces a wider ara of deformation, magmatism, and surface restructuring. As a result, the structural signal of the underlying convection is expressed not only with a single line, but across a much wider region.

This broader influence is clearly reflected in the landscape. The rivers of southern Iceland do not flow randomly; their courses frequently align with the same geometric trend as the Reykjanes Ridge. When viewed from this perspective, their paths are not merely shaped by local topography, but are part of a larger, coherent tectonic pattern. Recognizing this connection is important. Everyone knows this trend, but general trend is not the same as accurate mathematical equation. This is how over a century of accurate measurements and mapping can be used to take an additional step towards understanding tectonics of the surface, and of course the inner structure of the Earth.