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Strandflat ( no , strandflate) is a landform typical of the Norwegian coast consisting of a flattish
erosion surface In geology and geomorphology, an erosion surface is a surface of rock or regolith that was formed by erosion and not by construction (e.g. lava flows, sediment deposition) nor fault displacement. Erosional surfaces within the stratigraphic ...
on the coast and near-coast
seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
. In Norway, strandflats provide room for settlements and
agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled peop ...
, constituting important
cultural landscape Cultural landscape is a term used in the fields of geography, ecology, and heritage studies, to describe a symbiosis of human activity and environment. As defined by the World Heritage Committee, it is the "cultural properties hatrepresent the ...
s. The shallow and protected waters of strandflats are valued fishing grounds that provide sustenance to traditional fishing settlements. Outside Norway proper, strandflats can be found in other high-latitude areas, such as
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest co ...
,
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S ...
, the Canadian Arctic, the Russian Far North,
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is ...
, Svalbard, Sweden and
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to th ...
. The strandflats are usually bounded on the landward side by a sharp break in slope, leading to mountainous terrain or high plateaux. On the seaward side, strandflats end at submarine slopes. The
bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of be ...
surface of strandflats is uneven and tilts gently towards the sea. The concept of a strandflat was introduced in 1894 by Norwegian geologist Hans Reusch.


Norwegian strandflat


Characteristics

Strandflats are not fully flat and may display some local relief, meaning that it is usually not possible to assign them a precise elevation above sea level. The Norwegian strandflats may go from above sea level to below sea level. The undulations in the strandflat relief may result in an irregular coastline with skerries, small embayments and peninsulas. The width of the strandflat varies from a few kilometers to 50 km and occasionally reaching up to 80 km in width. From land to sea the strandflat can be subdivided into the following zones: the supramarine zone, the skjærgård (skerry archipelago), and the submarine zone. Residual mountains surrounded by the strandflat are called rauks. On the landward side, the strandflat often terminates abruptly with the beginning of a steep slope that separates it from higher or more uneven terrain. In some locations this sharp boundary is lacking and the landward end of strandflat is diffuse. On the seaward side, the strandflat continues underwater down to depths of , where a steep submarine slope separates it from older low relief paleic surfaces. These paleic surfaces are known as bankflat, and make up much of the continental shelf. At some locations, the landward end of the strandflat or the region slightly above contains relict sea caves partly filled with sediments that predate the last glacial period. These caves lie near the post-glacial marine limit or above it. Overall, strandflats in
Nordland Nordland (; smj, Nordlánnda, sma, Nordlaante, sme, Nordlánda, en, Northland) is a county in Norway in the Northern Norway region, the least populous of all 11 counties, bordering Troms og Finnmark in the north, Trøndelag in the south, ...
are larger and flatter than those of
Western Norway Western Norway ( nb, Vestlandet, Vest-Norge; nn, Vest-Noreg) is the region along the Atlantic coast of southern Norway. It consists of the counties Rogaland, Vestland, and Møre og Romsdal. The region has no official or political-administrat ...
. Also in Nordland, many strandflats are found next to active seismic faults.


Geological origin

Despite being together with
fjord In physical geography, a fjord or fiord () is a long, narrow inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Alaska, Antarctica, British Columbia, Chile, Denmark, Germany, Greenland, the Faroe Islands, Icela ...
s the most studied coastal landform in Norway, as of 2013 there is no consensus as to the origin of strandflats. An analysis of the literature shows that during the course of the 20th century, explanations for the strandflat shifted from involving one or two processes to including many more. Thus most modern explanations are of polygenetic type. Grand-scale observations on the distribution of strandflats tend to favour an origin in connection to the
Quaternary glaciation The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describ ...
s, while in-detail studies have led scholars to argue that strandflats have been shaped by chemical weathering during the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Creta ...
. According to this second view, the weathered surface would then have been buried in sediments to be freed from this cover during Late Neogene for a final reshaping by erosion.
Hans Holtedahl Hans Holtedahl (8 December 1917 – 24 February 2001) was a Norwegian geologist. He was a professor of geology at the University of Bergen. Biography He was born in Krisitania (now Oslo, Norway) a son of geologist Olaf Holtedahl (1885–19 ...
regarded the strandflats as modified paleic surfaces, conjecturing that paleic surfaces dipping gently to the sea would favoured strandflat formation. In his original description, Reusch regarded the strandflat as originating from
marine abrasion Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...
prior to glaciation, but adding that some levelling could have been caused by non-marine erosion. In his view, the formation of the strandflat preceded the
fjords of Norway This list of Norwegian fjords shows many of the fjords in Norway. In total, there are about 1,190 fjords in Norway and the Svalbard islands. The sortable list includes the lengths and locations of those fjords. Fjords See also * List of gla ...
. Years later, in 1919, Hans Ahlmann assumed the strandflat formed by erosion on land towards a base level. In the mid-20th century, W. Evers argued in a series of publications that the strandflat was a low-erosion surface formed on land as part of a stepped sequence ( piedmonttreppen) that included the Paleic surfaces. This idea was refuted by Olaf Holtedahl, who noted that the position of the surfaces were not that of a piedmonttreppen.


Frost weathering, glaciers and sea ice

The Arctic explorer
Fritjof Nansen Fridtjof Wedel-Jarlsberg Nansen (; 10 October 186113 May 1930) was a Norwegian polymath and Nobel Peace Prize laureate. He gained prominence at various points in his life as an explorer, scientist, diplomat, and humanitarian. He led the team t ...
agreed with Reusch that marine influences formed the strandflat, but added in 1922 that
frost weathering Frost weathering is a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedgi ...
was also of key importance. Nansen discarded ordinary marine abrasion as an explanation for the formation of the strandflat, as he noted that much of the strandflat lay in areas protected from major waves. In his analysis, Nansen argued that the strandflat formed after the fjords of Norway had dissected the landscape. This, he argued, facilitated marine erosion by creating more coast and by creating nearby
sediment sink Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
s for eroded material. In 1929, Olaf Holtedahl favoured a glacial origin for the strandflat, an idea that was picked up by his son
Hans Holtedahl Hans Holtedahl (8 December 1917 – 24 February 2001) was a Norwegian geologist. He was a professor of geology at the University of Bergen. Biography He was born in Krisitania (now Oslo, Norway) a son of geologist Olaf Holtedahl (1885–19 ...
. Hans Holtedahl and E. Larsen went on to argue in 1985 for an origin in connection to the Quaternary glaciations with material loosened by
frost weathering Frost weathering is a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedgi ...
, and sea-ice transporting loose material and making the relief flat. Tormod Klemsdal added in 1982 that cirque glaciers could have made minor contributions in "widening, levelling and splitting the strandflat".


Deep weathering and antiquity

Contrary to the glacial and
periglacial Periglaciation (adjective: "periglacial", also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and ...
hypotheses, Julius Büdel and Jean-Pierre Peulvast regard
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movemen ...
of rock into
saprolite Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops its color comes from ferric compounds. Deeply weathered profiles are widesprea ...
as important in shaping the strandflat. Büdel held that weathering took place in a distant past with tropical and sub-tropical climates, while Peulvast considered that present-day conditions and a lack of glaciation were enough to produce the weathering. As such, Peulvast considered the saprolite found in the strandflat, and the weathering that produced it, to predate the Last glacial period and possibly the
Quaternary glaciation The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describ ...
s. For Büdel, the strandflat was a surface shaped by weathering dotted with inselbergs. In 2013, Odleiv and co-workers put forward a mixed origin for the strandflat of
Nordland Nordland (; smj, Nordlánnda, sma, Nordlaante, sme, Nordlánda, en, Northland) is a county in Norway in the Northern Norway region, the least populous of all 11 counties, bordering Troms og Finnmark in the north, Trøndelag in the south, ...
. They argue that this strandflat in northern Norway could represent the remnants of a weathered peneplain of
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
age that was buried in sediment for long time before made flat again by erosion in
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the '' Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed ...
times. A 2017 study concerning
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...
of illite, a clay formed by weathering, is interpreted to indicate that the strandflat at
Bømlo Bømlo is a municipality in the southwestern part of Vestland county, Norway. It is located in the traditional district of Sunnhordland. The administrative centre of the municipality is the village of Svortland. Other villages in Bømlo inclu ...
in
Western Norway Western Norway ( nb, Vestlandet, Vest-Norge; nn, Vest-Noreg) is the region along the Atlantic coast of southern Norway. It consists of the counties Rogaland, Vestland, and Møre og Romsdal. The region has no official or political-administrat ...
was weathered ''c''. 210 million years ago during
Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...
times. Haakon Fossen and co-workers disagree with this view citing
thermochronology Thermochronology is the study of the thermal evolution of a region of a planet. Thermochronologists use radiometric dating along with the closure temperatures that represent the temperature of the mineral being studied at the time given by the da ...
studies to claim that the strandflat in Western Norway was still covered by sedimentary rock in the Triassic and did only got free of its sedimentary cover in the Jurassic. Same authors note that movement of geological faults in the Late Mesozoic imply the strandflats of Western Norway took their final shape after the
Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the ...
or else they would occur at various heights above sea level. A similar opinion is expressed by Hans Holtedahl who wrote that " e strandflat must have formed later the main (
Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non- avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...
) uplift of the Scandinavian landmass". To this Holtedahl added that in
Trøndelag Trøndelag (; sma, Trööndelage) is a county in the central part of Norway. It was created in 1687, then named Trondhjem County ( no, Trondhjems Amt); in 1804 the county was split into Nord-Trøndelag and Sør-Trøndelag by the King of Denmar ...
between Nordland and Western Norway the strandflat could be a surface formed before the Jurassic, then buried in sediments and at some point freed from this cover. In the understanding of Tormod Klemsdal strandflats may be old surfaces shaped by deep weathering that escaped the uplift that affected the
Scandinavian Mountains The Scandinavian Mountains or the Scandes is a mountain range that runs through the Scandinavian Peninsula. The western sides of the mountains drop precipitously into the North Sea and Norwegian Sea, forming the fjords of Norway, whereas to the ...
further east. The strandflat at Bømlo is considered by Ola Fredin and co-workers to be equivalent to the sediment-capped top of Utsira High offshore west of
Stavanger Stavanger (, , US usually , ) is a city and municipality in Norway. It is the fourth largest city and third largest metropolitan area in Norway (through conurbation with neighboring Sandnes) and the administrative center of Rogaland county. T ...
. This view is also disputed by Haakon Fossen and co-workers who state that the
basement A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the Furnace (house heating), furnace, ...
surface under the northern
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...
formed not at a single time.


Outside Norway

Strandflats have been identified in high-latitude areas such as the coast of
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S ...
, Arctic Canada,
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is ...
, Svalbard,
Novaya Zemlya Novaya Zemlya (, also , ; rus, Но́вая Земля́, p=ˈnovəjə zʲɪmˈlʲa, ) is an archipelago in northern Russia. It is situated in the Arctic Ocean, in the extreme northeast of Europe, with Cape Flissingsky, on the northern island ...
and
Taymyr Peninsula The Taymyr Peninsula (russian: Таймырский полуостров, Taymyrsky poluostrov) is a peninsula in the Far North of Russia, in the Siberian Federal District, that forms the northernmost part of the mainland of Eurasia. Administrat ...
in Russia and the western coasts of Sweden and
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to th ...
. These strandflats are usually smaller than the Norwegian. In
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest co ...
strandflats can be found in the
Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...
as well as in the
South Shetland Islands The South Shetland Islands are a group of Antarctic islands with a total area of . They lie about north of the Antarctic Peninsula, and between southwest of the nearest point of the South Orkney Islands. By the Antarctic Treaty of 195 ...
. In addition there have been mentions of strandflats in
South Georgia Island South Georgia ( es, Isla San Pedro) is an island in the South Atlantic Ocean that is part of the British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around east of the Falkland Islands. Stretching in the eas ...
. In
Robert Island Robert Island or Mitchells Island or Polotsk Island or Roberts Island is an island long and wide, situated between Nelson Island and Greenwich Island in the South Shetland Islands, Antarctica. Robert Island is located at . Surface area . ...
in the South Shetland Islands raised strandflats show that the island has been subject to a relative change in sea level. Raised
shore platform A wave-cut platform, shore platform, coastal bench, or wave-cut cliff is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by erosion. Wave-cut platforms are often most obvi ...
s corresponding to strandflats have also been identified in Scotland's
Hebrides The Hebrides (; gd, Innse Gall, ; non, Suðreyjar, "southern isles") are an archipelago off the west coast of the Scottish mainland. The islands fall into two main groups, based on their proximity to the mainland: the Inner and Outer Hebrid ...
. Possibly these formed in
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Quaternary glaciation The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describ ...
s.


Gallery

File:Siggjo viewed towards east.JPG, Aerial view of the strandflat at
Bømlo Bømlo is a municipality in the southwestern part of Vestland county, Norway. It is located in the traditional district of Sunnhordland. The administrative centre of the municipality is the village of Svortland. Other villages in Bømlo inclu ...
. File:Southern_Goddo.JPG, Aerial view of the strandflat at Goddo island near Bømlo. File:Leaving_Lochmaddy_-_geograph.org.uk_-_929584.jpg, Skerry zone of a strandflat in
Lochmaddy Lochmaddy ( gd, Loch nam Madadh, "Loch of the Hounds") is the administrative centre of North Uist in the Outer Hebrides, Scotland. ''Na Madaidhean'' (the wolves/hounds) are rocks in the bay after which the loch, and subsequently the village, are ...
,
Hebrides The Hebrides (; gd, Innse Gall, ; non, Suðreyjar, "southern isles") are an archipelago off the west coast of the Scottish mainland. The islands fall into two main groups, based on their proximity to the mainland: the Inner and Outer Hebrid ...
. File:Helgeland coast.jpg, View of the strandflat at Helgeland from the mountain Dønnesfjellet in Dønna. A number of ''rauks'' can be seen, from left:
Træna Træna is a municipality in Nordland county, Norway. It is part of the Helgeland traditional region. The administrative centre of the municipality is the island/village of Husøya. Other population centres include Selvær and Sanna. Fishing ...
, Lovunda, Selvær, Nesøya, Hestmona, Rødøyløva and Lurøyfjellet, all landmarks on the Norwegian Coast.


Explanatory footnotes


Citations


General literature

* * Nansen, Fridtjof (1904). "The Bathymetrical Features of the North Polar Seas". In Nansen F. (ed.): ''The Norwegian North Polar Expedition 1893–1896. Scientific results'', Vol IV. J. Dybwad, Christiania, 1–232. * Reusch, Hans (1894). ''Strandflaten, et nyt træk i Norges geografi''. Norges geologiske undersokelse, 14, 1–14. {{Geology of Fennoscandia Coastal and oceanic landforms Geology of the North Sea Glacial erosion landforms Periglacial landforms Plains of Norway Planation surfaces Unconformities Weathering landforms