Читать книгу Iceland Within the Northern Atlantic, Volume 1 - Группа авторов - Страница 23

Since its insularization, 16 My ago, Iceland has formed a volcanic land located in a central position in the Atlantic Ocean, a site subject to numerous effusive fissural eruptions. Therefore, it is also one of the main areas of the northern hemisphere generating explosive eruptions emitting into the atmosphere ashes, tephra and gases.

Icelandic quaternary volcanism allows us to understand, by its outcrop along coastal cliffs or canyons, the mechanisms of formation of numerous eruptive figures in aerial or underwater basaltic environments. This is the case of rootless volcanoes and lava lakes (section 1.2 of Volume 2), the establishment of dykes or sills and their control by tectonics, or the evolution of stresses related to glaciations. We have shown that close mechanical and physical links probably exist between deglaciation, volcanism, seismicity and tectonic deformations (section 2.1 of Volume 2). The key process lies in variations in the adiabatic melting rate of the mantle near the lithosphere/asthenosphere boundary, induced by decompression related to crustal extension or glacio-isostatic discharge. The emission zones of these lava flows have therefore constrained the evolution of Iceland since the onset of glaciations. It also enabled the understanding of the formation of SDRs (Seaward Deeping Reflectors), a mode of accumulation of lava flows especially recognized by seismic reflection along the margins of the North Atlantic.

Tephra successions are commonly recorded in the cores drilled in the Greenland ice cap and in marine sediments deposited on the bottom of the North Atlantic. Some of these tephras were distally dated by radiocarbon as in the peat bogs of northern Europe, others by age patterns in ice or marine sedimentary accumulations (sections 1.3 and 3.2 of Volume 2). More rarely, their dating has been performed directly by K-Ar analysis (section 2.4 of Volume 2). These emissions of tephra and associated gases have a significant environmental impact on ocean fertility, as the GIFR seabed is an important breeding ground for the majority of fish consumed, as well as on the health of human or animal populations and on air safety, as shown by the recent eruption of Eyjafjallajökull (2010).