Silfra ( Icelandic pronunciation: [ˈsɪl(v)ra] ) is a rift formed in the Mid-Atlantic Ridge – the divergent tectonic boundary between the North American and Eurasian plates – and is located in the Þingvallavatn Lake in the Þingvellir National Park in Iceland .
22-581: Silfra lies in the Þingvellir valley and within the Þingvellir National Park. The valley, and Silfra itself, were formed by the divergent tectonic drift of the Eurasian and North American plates. The plates drift about 2 cm (0.79 in) farther apart every year, building up tension between the plates and the earth mass above. This tension is relieved through periodic major earthquakes at approximately ten-year intervals, which have caused cracks and fissures to form in Þingvellir valley; Silfra lies at
44-438: A strong current that flushes every diver straight down. Although this practice is no longer allowed due to the instability of the tunnel, it still holds importance because it is the entrance to the cave. Towards the end of the fissure, it opens up to a shallow lagoon with the most visibility covered in green algae. It is about 120 metres (390 ft) long and is used as the exit point for divers and snorkelers. The water temperature
66-465: A tectonic plate world map. For purposes of this list, a microplate is any plate with an area less than 1 million km . Some models identify more minor plates within current orogens (events that lead to a large structural deformation of Earth's lithosphere ) like the Apulian, Explorer, Gorda, and Philippine Mobile Belt plates. The latest studies have shown that microplates are the basic elements of which
88-418: Is a list of ancient cratons , microplates , plates , and terranes which no longer exist as separate plates. Cratons are the oldest and most stable parts of the continental lithosphere, and shields are exposed parts of them. Terranes are fragments of crustal material formed on one tectonic plate and accreted to crust lying on another plate, which may or may not have originated as independent microplates:
110-623: Is between 2–4 °C (36–39 °F) but can be comfortably dived using a dry suit . Although aquatic life is scarce in the extremely cold water temperatures, it is a habitat for some such as the amphipod called Crymostygius Thingvallensis found only in Thingvellir Lake and the surrounding fissures. A fish species called the Arctic Char also occasionally venture into Silfra during mating season in August and September. However,
132-832: The Anatolian sub-plate and the Arabian plate . The Anatolian sub-plate is currently being squeezed by the collision of the Eurasian plate with the Arabian plate in the East Anatolian Fault Zone . The boundary between the North American plate and the Eurasian plate in the area around Japan has been described as "shifty". There are different maps for it based on recent tectonics, seismicity and earthquake focal mechanism . The simplest plate geometry draws
154-520: The 1783 eruption of Laki and the 2010 eruption of Eyjafjallajökull , are caused by the North American and the Eurasian plates moving apart, which is a result of divergent plate boundary forces. The convergent boundary between the Eurasian plate and the Indian plate formed the Himalayas mountain range. The geodynamics of Central Asia is dominated by the interaction between the Eurasian plate and
176-789: The Indian plate. In this area, many sub-plates or crust blocks have been recognized, which form the Central Asian and the East Asian transit zones. List of tectonic plates This is a list of tectonic plates on Earth's surface . Tectonic plates are pieces of Earth's crust and uppermost mantle , together referred to as the lithosphere . The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium ) and continental crust ( sial from silicon and aluminium ). The composition of
198-539: The Silfra fissure. Silfra is spring fed by groundwater originating as meltwater from Langjökull , Iceland's second largest glacier , about fifty kilometres north of the Þingvallavatn Lake. In the distant past, this Langjökull meltwater ran through a river directly and unimpeded into the Þingvallavatn Lake. This river was blocked a few thousand years ago by lava flows from the Skjaldbreiður volcano causing
220-701: The boundary from the Nansen Ridge through a broad zone of deformation in North Asia to the Sea of Okhotsk then south through Sakhalin Island and Hokkaido to the triple junction in the Japan Trench . But this simple view has been successfully challenged by more recent research. During the 1970s, Japan was thought to be located on the Eurasian plate at a quadruple junction with the North American plate when
242-664: The bulk of the continents and the Pacific Ocean . For purposes of this list, a major plate is any plate with an area greater than 20 million km (7.7 million sq mi) These smaller plates are often not shown on major plate maps, as the majority of them do not comprise significant land area. For purposes of this list, a minor plate is any plate with an area less than 20 million km (7.7 million sq mi) but greater than 1 million km (0.39 million sq mi). These plates are often grouped with an adjacent principal plate on
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#1732780924679264-413: The continental rift. Silfra is about a 45 to 60-minute drive east of Iceland's capital Reykjavik . There are three main dive sites: Silfra Hall, Silfra Cathedral, and Silfra Lagoon. The Silfra Hall consists of multiple cave systems underwater with a maximum depth of about 45 metres.The Cathedral is a 100 metres (330 ft) long fissure with visibility almost from end to end. Shallow at the entry points and
286-420: The crust is composed and that the larger plates are composed of amalgamations of these, and a subdivision of ca. 1200 smaller plates has come forward. In the history of Earth, many tectonic plates have come into existence and have over the intervening years either accreted onto other plates to form larger plates, rifted into smaller plates, or have been crushed by or subducted under other plates. The following
308-586: The eastern boundary of the North American plate was drawn through southern Hokkaido . New research in the 1990s supported that the Okhotsk microplate was independent from the North American plate and a boundary with the Amurian microplate , sometimes described as "a division within the Eurasian plate" with an unknown western boundary. All volcanic eruptions in Iceland, such as the 1973 eruption of Eldfell ,
330-426: The ends of the fissure, Silfra descends to a maximum depth of 63 metres (207 ft) but diving to this depth is seldom done as it requires technical diving skills. To get to the main part of Silfra from the caves, divers must go down through the "toilet" headfirst which is a narrow tunnel to a depth of 16 metres. It is the only opening from the Silfra cave to the Silfra crack for the water to go through, thus creating
352-451: The meltwater to pond and seep underground into the porous lava rock to form an aquifer . This water then percolates through the aquifer for thirty to a hundred years before emerging from the fissure springs in the Þingvallavatn Lake fifty kilometres to the south. The emerging, highly filtered groundwater is exceptionally clear and potable . Scuba diving and snorkeling in Silfra are popular because of its clear water and location within
374-464: The month of June in 930 CE marked Iceland's birth. The sessions continued until the year 1798 when it was then replaced by the High Court until it was reinstated about 50 years later. Ruins of the ancient stone "booths" are still visible and visitors can walk between two tectonic plates. Visitors can look out from the uplifted tectonic ridgeline and see the numerous fissures varying in size as well as
396-582: The only fish life that lives in the fissure year-round is the Dwarf Char, a subspecies of the Arctic Char. They are rarely seen because they live in the deeper and darker recesses of the fissure. 64°15′16″N 21°07′05″W / 64.254323°N 21.117958°W / 64.254323; -21.117958 Cave dive sites: Eurasian Plate The Eurasian plate is a tectonic plate that includes most of Eurasia (a landmass consisting of
418-452: The rim of the Þingvallavatn Lake and is one of the largest and deepest of these fissures. The Silfra fissure intercepts a major aquifer, which feeds multiple springs at its base. Boulders and rocks falling into the widening cracks have formed caves within the fissures. Þingvellir (Thingvellir) National Park is a UNESCO world heritage area and home to Iceland's first parliamentary assembly called Althingi . The initial two-week meeting in
440-540: The seismically active Azores triple junction extending northward along the Mid-Atlantic Ridge towards Iceland . Ridges like the Mid-Atlantic ridge form at a divergent plate boundary . They are located deep underwater and very difficult to study. Scientists know less about ocean ridges than they do the planets of the solar system. There is another triple junction where the Eurasian plate meets
462-681: The traditional continents of Asia and Europe ), with the notable exceptions of the Arabian Peninsula , the Indian subcontinent , and the area east of the Chersky Range in eastern Siberia . It also includes oceanic crust extending westward to the Mid-Atlantic Ridge and northward to the Gakkel Ridge . The western edge is a triple junction plate boundary with the North American plate and Nubian plate at
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#1732780924679484-541: The two types of crust differs markedly, with mafic basaltic rocks dominating oceanic crust, while continental crust consists principally of lower- density felsic granitic rocks. Geologists generally agree that the following tectonic plates currently exist on Earth's surface with roughly definable boundaries. Tectonic plates are sometimes subdivided into three fairly arbitrary categories: major (or primary ) plates , minor (or secondary ) plates , and microplates (or tertiary plates ). These plates comprise
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