Iceland Within the Northern Atlantic, Volume 1. Группа авторов

Figure I.22. A subglacial tabular volcano: the Herðubreið, north of Vatnajökull, North Volcanic Zone (Brigitte Van Vliet-Lanoë©)

Figure I.23. Jökulsá á Kreppa north of Vatnajökull with hyaloclastite or tindar ridges (Brigitte Van Vliet-Lanoë©)

Figure I.24. A key Icelandic resource: water. (A) Bruarjökull outlet (the glacier is at the bottom of the photograph) (LMIs©). (B) One of the Dettifoss waterfalls (Jökulsá á Fjöllum). (C) The Haslsón dam on the Jökulsá á Brú. (D) The Fannahlið aluminum plant (Hvalfjörður) (photos B, C and D: Brigitte Van Vliet-Lanoë©)

On land, Iceland’s only important and renewable resources are its water and, as a result, its hydroelectricity, as well as its many geothermal sites related to the presence of the hot spot.

      In this two-volume book, we will present the geological and glacial history of this island, its current tectonic and volcanic activity and the impact of its formation on the climatic evolution of the last few millions of years. Volume 1 replaces Iceland within the geological framework of the North Atlantic, and describes its tectonic and geodynamic evolution. Volume 2 (Van Vliet-Lanoë 2021) is dedicated to the study of the interactions between Icelandic volcanism and external geodynamics, i.e. with glaciations and the climatic evolution of the Atlantic zone during the Neogene and the Quaternary.

      For color versions of the figures in this Introduction see, www.iste.co.uk/vanvliet/iceland1.zip.

      1

      Iceland, in the Lineage of Two Oceans

       Brigitte VAN VLIET-LANOË and Françoise BERGERAT with the collaboration of René MAURY, Hervé GUILLOU and Laurent GEOFFROY

There is no active region on Earth comparable to Iceland and its ocean environment (Figure 1.1). Situated in the Northeast Atlantic, Iceland is indeed located within a particularly complex geodynamic evolutionary domain, illustrating the problems inherent to the break-up of continents in the plate tectonic model, especially the recycling of ancient structures such as the suture of the Iapetus Ocean (section 3.2.2.3) and its paleoslab active during the Silurian. The latter has been mapped along the eastern coast of Greenland and is associated with calc-alkaline palaeo-volcanism (Andresen et al. 2007; Rhenström 2010).

      The existence of Iceland probably dates back to the Oligocene. Its position east of Greenland and its insularization make it a key witness of the great changes controlling the evolution of the oceanic circulation. It has thus controlled the evolution of the climate since the Neogene, through the North Atlantic Current. It has also been, since 9 My, a key recorder of the onset of glaciation in the northern hemisphere, and also of glacier–volcanism interactions. Its location in the middle of the Greenland–Faroe Islands Ridge (GFIR) controls the descent of cold salty waters from the Arctic and North Atlantic into the thermohaline circulation section 3.4 of Volume 2).

Figure 1.1 summarizes the broad physiographic features and toponymy of the different structural domains (ridges and basins) of the North Atlantic and the Labrador-Baffin axis (LBA) on both sides of Greenland.

Figure 1.1. The Northeast Atlantic Ocean and the Labrador–Baffin axis (Gebco 2019 base, L. Gernigon processing)

      These submerged domains are made up of lithospheres of oceanic and continental nature (section 3.2) with, sometimes, uncertain limits between these two types.

The emerged geology of Iceland shows a relatively recent differentiation. Large outcrops of so-called ancient basalts (15–5 My, in blue in Figure 1.2(b)) occupy coastal areas and are overlain by younger lavas (between 5 and 7 My, in green). This second generation of basalts is itself intersected by an active rift zone associated with Pleistocene (gray) and Holocene (pink) volcanism that crosses the whole island from south to north. In addition, four ice sheets cap presently the island in relation with especially wide brown bands (Figure 1.2(b)), which are the traces of subglacial volcanism, witnesses of a wider extension of the glaciers. It is also associated with a strong sedimentary splay along its southern coast (in light blue). Iceland has thus experienced a very complex history.

      Figure 1.2. (a) Geological map of Iceland, originally at 1/600,000e (H. Johanesson 2014). Náttúrufræðistofnun Ísland (Icelandic Institute of Natural History) (available at: https://en.ni.is/resources/publications/maps/geological-maps)

Figure 1.2. (b) Simplified geological map of Iceland (Icelandic Geographical Institute/Landmælingar Ísland)

1.1. Geographic and geodynamic context

The surface of Iceland appears as a vast plateau of about 600 m altitude (Figure 1.3, in orange), overlain by four large volcanic systems covered by four wide ice caps. Another surface, called strandflat, surrounds the island at about the level of the present coast and extends into the sea down to about −50 m; it is underlined by large swarms of small islands. Finally, a lowered submarine plateau surrounds the island to a depth of 300 m (Figure 1.3). The fact that it is cut by Neogene glacial scouring attests to its age (section 3.2 of Volume 2).

Figure 1.3. Current morphology of Iceland.