Thingvellir Fissure Zone Iceland meeting of the North American Plate the Euro Asian Plate
The Þingvellir area is a part of the North Atlantic rift system, almost entirely nested within the Reykjaneshryggur-Langjökull rift system. It can be described as an area of sea-floor spreading, displaying the close association of crustal rifting and volcanism. Þingvellir and the Great Rift Valley of Eastern Africa are the only sites on Earth where the effects of two major plates drifting apart can be observed. The rift zone constitutes a graben bounded by major faults. The rift valley narrows from about 20-25 km in the NE to about 10 km in the SW. The extension appears as nearly parallel fissures and down-dropped fault blocks running along the length of the valley. On the west (North American) side of the valley, the blocks step down toward the east, while the situation is reversed on the east (European) side. Thus the valley floor is a linear block that has subsided as the valley walls were pulled apart by plate motions. The valley walls are moving apart at a rate of about 7 mm per year, and during the past 9000 years the estimated horizontal extension is of the order of 70 m. The floor is subsiding at about 1 mm per year, with a total subsidence of 40 m for the past 9000 years. Rifting within the graben is episodical, with the last major earthquake activity occurring in 1789. During the 1789 earthquakes the graben floor subsidised 1-2 m.
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Photo credit: © Phil Degginger / Alamy / Afripics
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Keywords: american, asian, colliding, euro, euro-asian, faulting, faults, fissure, geological, geology, heritage, iceland, icelandic, north, plate, plates, rift, site, tectonics, thingvellir, unesco, vulcanism, world, zone, Þingvellir
