Each of Iceland’s volcanic systems shows a double character, meaning that the volcanic zone or belt tends to appear as a pair of structurally or spatially related units — in most cases corresponding to two adjacent polygons within the framework of the convection roll system. Since mantle convection rolls occur as paired structures, the volcanic systems that form above them naturally reflect this geometry. In this way, nearly every volcanic zone or belt in Iceland can be divided into two complementary parts.
West Volcanic Zone (WVZ) – The WVZ displays a continuous rifted region along its southwest portion, including the famous Þingvellir rift valley, and a secondary, wider area toward the northeast. Although the polygon northeast of the WVZ, here marked with a question mark, is commonly considered part of the same zone, its characteristics suggest it may instead be linked more closely with the Mid Iceland Belt.
East Volcanic Zone (EVZ) – The EVZ is sometimes defined as covering five polygons, but here only two, where active spreading takes place.
South Iceland Volcanic Belt (SIVB) – The SIVB also follows a paired pattern, the two polygons being quite different though, with Katla and Eyjafjallajökull in the southern one, and long fissures covering the northern one. Hekla is found between them, marking the division between spreading and non-spreading along the 64th latitude.
Westman Islands (WI) – The WI system is an exception, as it currently appears confined to a single polygon. However, if the general two-part pattern holds true, there should be a counterpart polygon located southwest of the islands. This hypothetical extension, designated as WI(2), would complement the known island polygon WI(1), completing the expected double structure. That is one part of science, right? Let’s go there and check it out!
Reykjanes Oblique Rift Zone (RORZ) – The RORZ demonstrates its double character both geographically and structurally. The Reykjanes Peninsula forms the onshore part of the system, while the offshore segment of the rift continues as a second polygon on the seafloor. These two parts together define the complete oblique rift zone.
Mid Iceland Belt (MIB) – The MIB is another exception to the general rule, as it occupies only one polygon in present definitions. However, given its central location and the symmetry of the convection roll system, it is logical to expect a complementary polygon in close proximity. The missing half of the MIB is therefore indicated by one of the question marks on the map. It is mainly up to petrologists to answer that question.
Skagafjörður Volcanic Belt (SKVB) – It volcanically extinct, and neglected, and even here I do not define the two parts 🙂
North Volcanic Zone (NVZ) – The NVZ can be divided into two principal parts: the northern portion associated with the Theistareykir–Krafla systems, and the southern portion extending toward Askja. These two subdivisions mark distinct volcanic corridors following separate polygons but functioning as a single rifting system.
Grímsey Oblique Belt (GOB) – The GOB likely mirrors the Reykjanes Oblique Rift Zone in both form and behavior. Its paired geometry supports its classification as an oblique twin to the RORZ.
Öræfajökull Volcanic Belt (ÖVB) – The double character of the ÖVB is particularly pronounced, as it clearly spans two distinct polygons: one centered on Öræfajökull and the other on Snæfell to the north. The two volcanic centers form a strongly defined pair, consistent with the structural control of the convection rolls beneath.
Snæfellsnes Volcanic Belt (SVB) – The SVB, is very similar to the ÖVB, and is divided into two parts here, although it actually extends over parts of 3 different polygons, it should not break the main rule of duality of each volcanic zone or volcanic belt.
In summary, the double character of Iceland’s volcanic systems reflects the paired arrangement of mantle convection rolls beneath the crust. Each volcanic zone or belt typically spans two adjacent polygons, forming a conjugate structure that mirrors the flow patterns of the underlying mantle. The only exceptions — MIB and WI — highlight potential locations where the complementary polygon remains unrecognized, indicated on the map by the two question marks.
Magic Magma 