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Þingvellir National Park is located on the northern shore of the Lake Þingvallavatn. It is about 240 km2 in size and its protection is based on the Þingvellir Conservation Act dating back to 1928. The national park was enlarged and the conservation status improved through better conservation and management with new legislation in 2004 by Act no. 47/2004 on Þingvellir National Park and by regulation no. 848/2005 on Þingvellir National Park. The old national park, part of the current national park, was inscribed on the World Heritage List in 2004 as a cultural landscape.
Þingvellir and Lake Þingvallavatn occupy a NE-SW elongated graben within the western branch of the rift zone in SW-Iceland. The rift zone represents the continuation of the Mid-Atlantic ridge across Iceland. Holocene lavas are most extensive in the central part of the graben, while Upper Pleistocene hyaloclastites and pillow lavas of sub-glacial origin and inter- or supraglacial lavas are most extensive at the periphery of the graben. All the rocks are basaltic.
The topography slopes gently away from the Langjökull glacier in the northeast towards the Reykjanes peninsula in the southwest. The Hengill central volcano closes the lake basin towards the southwest. The morphology and structure of the lake surroundings are strongly dominated by faults with throws of locally more than 100 m towards the actively sinking and expanding graben.
Water from the catchment area is filtered through lavas and hyaloclastites before emerging as springs within fractures and fissures at the shores of the lake. Lake Þingvallavatn and its catchment are almost entirely nested within the rift zone of SW-Iceland.
The presence of a glacier during the ice age had a profound effect on volcanism and the resulting volcanic landforms in the area. Within a glacier the interaction of melt water and magma leads to pillow lava formation, magma fragmentation and explosive activity. Ridges and mounds are built up of pillow lava, hyaloclastite tuffs, breccias and minor intrusions. If the eruptions break through the ice, subaerial cap lavas can form on top. The resulting landforms, called tindars and tuyas, are quite common around Þingvellir and in Iceland, but are exceedingly rare elsewhere.
Since the ice retreated from the area around 11.000 years ago volcanic eruptions have mainly produced lavas. Voluminous basaltic lavas flowed into the Þingvellir graben in early Holocene time (around 10.000 years ago). Most prominent are the lava shields of Skjaldbreiður to the northeast and Eldborgir to the east. Some of the lavas at Þingvellir and Gjábakki are thought to be from eruptions which occurred slightly earlier than Eldborgir. About 3.600 years ago a fissure eruption NE of Lake Þingvallavatn (northeast of Hrafnabjörg) produced the Þjófahraun lava, which extends towards Þingvellir. The youngest lava in the area, Nesjahraun, erupted from a crater row at the southwestern shore of Þingvallavatn about 2000 years ago. At the same time the phreatic tuff cone of Sandey was formed in the middle of the lake. Earlier lavas are also found at the southwestern shore of the lake.
A large geothermal system is associated with the Hengill central volcano to the southwest. Part of it extends towards the lake in the Nesjavellir area.
The faults and ground fissures in the vicinity of Þingvellir have been studied extensively and provide exceptionally clear evidence for continental drift and plate tectonics. The total amount of subsidence during the past 9.000 years is more than 40 m between Almannagjá and Hrafnagjá. During the same time horizontal extension of the graben has been estimated at about 70 m. The last tectonic event to hit the area occurred in 1789 when the area at the northern shore of Lake Þingvallavatn subsided by 1-2.6 m.
Situated about 100 m above sea level, Lake Þingvallavatn is the largest natural lake in Iceland with a surface area of approximately 84 km2, mean depth of 34 m and maximum depth of 114 meters and ca. 3 km3 (2.855 Gl) in volume. Close to 90% of all water entering the lake (ca. 100 m3 s-1) is cold (3-4° C), subterranean spring fed water. The lake is crystal clear, with Secchi depth visibility down to 12 m, oligotrophic in nature and with nitrogen as a limiting factor for primary production. The lake outlet, River Efra-Sog, is one of Europe's largest spring fed rivers, flushing out about 100 tons of water every second. The retention time of water in the lake is about one year.
The catchment area of Lake Þingvallavatn, about 1300 km2, lies in the same direction as the fissures in the area, and its existence is closely connected to the geological history. The majority of the catchment area is covered by neovolcanic lava, through which water easily drains. Due to the young age and volcanic nature of the bedrock, it contains high levels of soluble minerals. Consequently, there is a high uptake of minerals in the groundwater as it percolates through the lava, and the spring fed water entering the lake is therefore rich in minerals. The great diversity of life in Lake Þingvallavatn can be traced back to these processes, as algae and plants, food for invertebrates, make use of the abundant nutrients in the water. The catchment area is protected by regulation no. 650/2006 that applies to the entire watershed area from Langjökull glacier.
The lake is particularly fertile and rich in vegetation, despite the very cold temperatures. A third of the bottom area down to a depth of 10 m is covered by ephytic diatoms whereas between 10-20 m depth there is a zone of quite tall (up to 50 cm) and dense stands of charophytes.
The fish in the lake
In general, Iceland is rather poor in species numbers, whether in fauna or flora. The main reason is a combination of isolation, i.e. the long distance between Iceland and the mainland, along with relatively short colonisation time since the end of the last Ice Age and rather tough climatic conditions. In turn, populations of existing species are often large. Moreover, they show a high degree of intraspecific variability in morphology, life history and use of habitat and food - a feature termed resource polymorphism in evolutionary biology. Low numbers of species, lack of interspecific competition and diversity of habitats (empty niches) are thought to be key factors in promoting intraspecific resource polymorphism and sympatric speciation among vertebrates.
Lake Þingvallavatn is abundant in fish. Three of the five species of freshwater fish found in Iceland, brown trout (Salmo trutta), Arctic charr (Salvelinus alpinus) and three-spine stickleback (Gasterosteus aquleatus) live in the lake. The Arctic charr is most abundant, with an estimated biomass of 700 tons and annual production of 300 tons for fish one year old and older. In the late 1980s and early 1990s, annual catch of charr from the lake ranged between 40-70 tons. For a deep, cold subarctic lake, such a high fish production is rare.
The presence of four Arctic charr morphs in the lake, representing one of the most spectacular examples of resource polymorphism among fish in the Subarctic, gives the lake a special status. Differentiation of charr into two specialized sympatric sub-populations within lakes is recognized throughout the northern hemisphere, but Lake Þingvallavatn is the only lake in the Subarctic where four charr morphs are known to exist sympatrically. Moreover, the morphology and ecology of the Arctic charr morphs in Lake Þingvallavatn are much more distinct and dissimilar from each other than in other lakes. Recent studies on sticklebacks also show that two different morphs of this species exist in the lake.
Based on geological evidence, it is known that evolution of the Arctic charr morphs has taken place within Lake Þingvallavatn. This evolutionary event has been going on for only 10.000 years at most, or for only ca. 3.000 generations of fish. Although some reproductive mixing occurs between the morphs in Lake Þingvallavatn, they may in fact now be considered as distinct species. The rapid evolution and diversification of the Arctic charr in the lake is attributed mainly to habitat stability and diversity, limited competition with other species and intense competition within the charr population itself. Regarding the habitat factor, scientists have underpinned the important role of the young, uneroded lava in the area, both with respect to physiochemical effects on the water body, and to physical properties of the lava bedrock, with its complex surface textures and three-dimensional spaces for fish to occupy.
The subterranean amphipods
In 1998, a new endemic family of subterranean gammaridean amphipod (Crustacea), was discovered in Iceland, representing a new species and genus to science, Crymostygius thingvallensis, found in spring inlets feeding Lake Þingvallavatn. This was the first report of a stygobiont freshwater amphipod from Iceland and the northernmost report of a stygobiont species in Europe. In 2000 another new species to science, Crangonyx islandicus, was discovered at Lake Þingvallavatn. There are indications that this species may have survived the Quarternary glacial period in sub-glacial refuge, e.g. in the groundwater of the porous lava, and even that they have persisted in Iceland for millions of years.
Vegetation and wildlife
Birch woodland is characteristic of the Þingvellir area, indicated by the original name of the area in Icelandic: Bláskógar (literally "Blue Woods"). In the National Park, 172 species of higher plants have been found, or about 40% of the Icelandic flora. Birch, dwarf birch and willow, plants of the heath family, transform the appearance of Þingvellir in autumn, and many visitors make their way there to enjoy the beauty of its pastel colours.
Lake Þingvallavatn is particularly deep and thus does not attract as many waterfowl as do shallower lakes such as Lake Mývatn. Generally, 52 bird species live by the lake while 30 others come and go. The most famous bird is the great northern diver which nests in a few places by the lake. It is grouchy and protects its territory energetically.
The Outstanding Universal Value of Þingvellir as a cultural landscape has already been confirmed by the inscription on the World Heritage List in 2004 under criteria III and VI. The Þingvellir area is also a natural wonder on a global scale, with the geologic history and the biota of Lake Þingvallavatn and its catchment area forming a unique entity, a magnificent showcase in geology and biology and an extraordinary ecosystem. The area is part of the world rift system which is normally a sub-oceanic feature. Being subaerial, Iceland is a rare exception of a mature oceanic rift system. This is caused by high volcanic production associated with an upwelling mantle plume beneath Iceland. Being able to witness the evolution and formation of new species of life in Lake Þingvallavatn - the diversification of the Arctic charr (Salvelinus alpinus) into four different morphs, is of immense value, as is the recent discovery of two new species to science of blind „cave" animals, the subterranean amphipod crustaceans (Crymostygius thingvallensis and Crangonyx islandicus), inhabiting spring fed groundwater inlets in the catchment area.
Criterion (vii): The landscape at Þingvellir has beautiful and mystical forms created entirely by continental drift, volcanism and glacial interaction. The three fundamental natural phenomena which created Iceland can all be found at Þingvellir.
Criterion (viii): Þingvellir is an outstanding, visible example of the drift of the Eurasiatic and American Tectonic Plates. Unique geological and geomorphological processes of great international importance are taking place at Thingvellir.
Criterion (ix): Lake Þingvallavatn has the only known instance of Arctic charr (Salvelinus alpinus) which has evolved into four different forms in the same lake in a span of less than 10,000 years. The basis for this is the creation of new habitats through continental drift.
Criterion (x): A new endemic family of subterranean gammaridean amphipod (Crustacea) was discovered in the lake in 1998, representing a new species and genus to science, Crymostygius thingvallensis, and again in 2000 a new species to science, Crangonyx islandicus, was discovered at Lake Þingvallavatn.
Continued protection of Þingvellir from 1928 has maintained and conserved the integrity and pristine nature of the area. The national park was enlarged and the conservation status improved with new legislation in 2004 by the Þingvellir National Park Act no. 47/2004 and by regulation no. 848/2005 on Þingvellir National Park. The old national park, part of the current national park, was inscribed on the World Heritage List in 2004 as a cultural landscape.
The management plan for Þingvellir National park 2004-2024 contains the Þingvellir Commission's management plan and vision for the national park for the next twenty years. The plan provides guidance on the interaction of protection and utilisation, planning and operations. The master plan for Bláskógabyggð municipality 2004-2016, which includes the Þingvellir area, addresses and emphasizes the integrity of the area.
The main concern for the area and pressure that could threaten the integrity stems from tourism and development in the vicinity of Þingvellir National Park. Current legislation is considered adequate to safeguard the integrity of the area of natural heritage considered for nomination. Legislative Act no. 85/2005 on protection of Lake Þingvallavatn and its catchment area with relevant regulation no. 650/2006 safeguards the hydrological quality of the area.
Landforms resulting from volcanic activities under glaciers, known as tindars and tuyas, are quite common around Þingvellir and in Iceland, but are exceedingly rare elsewhere.
Volcanoes on the Mid-Atlantic Ridge are only visible above sea level in very few places, including Jan Mayen, the Azores and Tristan da Cunha. However, it is only in Iceland that the axis of the ridge can be observed.
In many respects, the Arctic charr morphs of Lake Þingvallavatn have much in common with the Darwin´s finches of the Galapagos Islands. The evolution of new species is at a much earlier stage in Lake Þingvallavatn though, due to the younger ecosystems.
Þingvellir, on the middle of the Mid-Atlantic Ridge, can be compared with the East African Rift Valley System, on account of the geological and limnological factors, in other words the places where the plates are drifting apart and forming lake landscapes. This comparison has not been performed, but is necessary as a part of a nomination process.