Þingvellir Tectonic Plates - Þingvellir, Iceland - Places of Geologic Significance on Waymarking.com

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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.
Almannagjá is 7.7 km long. Its greatest width is 64 m, and its maximum throw is 30-40 m. It marks the eastern boundary of the North American plate. Its equivalent across the graben, marking the western boundary of the Eurasian plate is Hrafnagjá. It is 11 km long, 68 m wide and has a maximum throw of 30 m. The Þingvellir faults are believed to be the surface expressions of deeply rooted normal faults. The numerous fissures encountered on the valley floor are of similar origin.
The bedrock of the Þingvallavatn catchment is consists mostly of postglacial lavas that are most extensive in the central part of the graben and Upper Pleistocene pillow lavas and hyaloclastites of subglacial origin and sub-aerial lavas. The Þingvellir graben is surrounded by volcanoes, that illustrate the connection between rifting and volcanism. Postglacial lava flows that measure estimated 30 km3 have flown into the graben, and fissure eruptions within the graben have left their marks.The Þingvellir lava (Þingvallahraun) floors the northern part of Lake Þingvallavatn and the graben floor north and east of the lake (dark green on the map above). It originated in a major fissure eruption to the southeast of Hrafnabjörg, around 9.100 years ago. The many single flows of this lava are best exposed in the fault scarp of Almannagjá, where numerous sheets of individual lava lobes have been successfully stacked as the eruption progressed."

Waymark is confirmed to be publicly accessible: yes Parking Coordinates: N 64° 15.517 W 021° 06.967 Access fee (In local currency): .00 Requires a high clearance vehicle to visit.: no Requires 4x4 vehicle to visit.: no Public Transport available: yes Website reference: [Web Link]

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