Threshold (geomorphology)

Sills (also called ridges ) in the sense of geomorphology are elevations of the earth's surface . They can be above or below sea ​​level ; so they rise on the mainland , on islands or in the ocean .

Emerging in the country

Thresholds that lie in the countryside or on the continents are often vast landscapes that have partly unfolded to form mountains or continue to unfold. Mighty continental plates can collide with each other, so that the thresholds are created by the tectonic forces that occur; This is accompanied in many places by volcanism (see for example the Central African Threshold ). These thresholds above-ground part fall at their edges into the continental shelves offshore seas off or they border on aboveground depression , pool and / or ( river ) - lowlands ; but sometimes they go over to highlands or mountains.

For example, there are these thresholds lying in the country (sorted alphabetically):

Africa

The five large African thresholds are, in addition to the Upper Guinea threshold , the following four thresholds arranged almost rectangularly around the Congo Basin :

• Lundaschwelle (as southern boundary)
• Lower Guinea Sill (as western boundary)
• North equatorial threshold (Asandeschwelle) (as northern boundary)
• Central African threshold (as eastern boundary)

Other African sleepers:

• Central Saharan Threshold
• South African Rand High Sill ( Great Rand Step )

Asia

Examples of emerging in Asia

• Kazakh threshold

Swell or back in the sea

Map of the worldwide lake basin

Swellings in the sea floor are called sea ​​ridges . In particular the respective main ridges of the individual oceans, the mid-ocean ridges . On earth, these ridges cover a total of around 70,000 km. They are mostly elongated mountain ranges . In many places on earth, their education is still ongoing.

Ridges of the sea arise mainly through the formation of new ocean crust at rift breaks , so-called "rift zones". In contrast, many mountain ranges on the mainland are formed by the collision of continental plates. In the apex regions of the mid-ocean ridges often form grave breaches of which many places magma rises, which as lava einquillt in the sea water and solidifies. The resulting ridges sometimes rise up to 3,000 m above the sea ​​floor , so that their peaks protrude above the sea surface. A good example of this is Iceland , where the North Atlantic Sill (viewed from the south) first rises above the surface of the island and then runs as a mountain ridge across Iceland, before sinking back into the depths of the Northern European Sea .

Ridges resulting from plate tectonics are not quite as common . In the submarine collision zones, either only oceanic plates or oceanic and continental plates collide. The thresholds that arise in front of the subduction zones created here usually rise geologically rapidly above sea level as a result of volcanic processes.

Examples of thresholds or ridges lying in the ocean and its marginal or secondary seas (sorted alphabetically):

Arctic Ocean

Swellings or ridges in the Arctic Ocean are:

• Fletcher Ridge (between the Central Arctic Basin in the north, Ellesmere Island in the east, the Canadian Basin in the south and the junction of the Canadian and Central Arctic Basin in the west)
• Gakkel Ridge (northern continuation of the North Atlantic Ridge ; divides the Eurasian Basin into the northern Amundsen Basin and the southern Nansen Basin )
• Lomonosov (Harris) Threshold (between the Geographic North Pole and the Eurasian Basin in the north, Greenland in the east, the Central Arctic Basin in the south and the New Siberian Islands in the west)
• East Siberian Threshold (between the junction of the Canadian and Central Arctic Basin in the north, the roughly parallel Chukchi Threshold in the east, Wrangel Island in the south, the East Siberian Sea in the southwest and the New Siberian Islands in the west)
• Chukchi Threshold (between the Canadian Basin in the north and east, the Chukchi Sea in the south, Wrangel Island in the southwest and the roughly parallel East Siberian Threshold in the west)

Atlantic Ocean

Thresholds or ridges in the Atlantic are:

• Atlantic-Indian Ridge (between the southern reaches of the Cape Basin and Cape Swell in the north, the Agulhas Basin in the northeast, the Crozet Swell in the east, the Atlantic-Indian South Polar Basin in the southeast, south and southwest and the southern extremity of the South Atlantic Ridge in the west and northwest)
• Azores threshold (between the Iberian Basin in the north, southwest Portugal and southwest Spain in the east, Madeira in the south, the Canary Basin in the southwest and the North Atlantic Ridge in the west; the Azores are at the interface between the Azores threshold and the last-mentioned threshold )
• Biscay Swell (between the Western European Basin in the north, northwestern Spain and northern Portugal in the east, the Iberian Basin in the south and the North Atlantic Ridge in the west)
• Falklands land level (see Falkland Ridge )
• Falkland Ridge (also called Falkland Landstufe ; between the Argentine Basin in the north and its southern foothills (behind which the South Georgian threshold adjoins) in the east, the Scotia Ridge in the south and the Falkland Islands in the west)
• Faroe Island Ridge (this is north-west in front of head Iceland , in the middle Faroe Islands , and south-east Scotland in front; between the Norwegian Basin in the north-east, the Shetland Sill in the south- east, the Iceland basin in the south-west and Iceland in the north-west)
• Guinea Sill (between the Guinea Basin in the northwest and north, São Tomé and Príncipe in the northeast, the Angola Basin in the east and southeast, St. Helena in the south and the South Atlantic Ridge in the west)
• Iceland-Jan-Mayen-Schwelle (as a northern part of the North Atlantic Ridge, it is located in the Northern European Sea between the Greenland Basin in the north, Bear Island in the northeast, the Lofot and Norwegian Basin in the east and southeast, the Jan Mayen Swell in the south, Iceland in the southwest and the Denmark Strait in the west; on the threshold is the island of Jan Mayen )
• Jan-Mayen-Schwelle (between the Iceland-Jan-Mayen-Schwelle in the north, the Lofot Basin in the northeast and east, the Norwegian Basin in the south and southwest and Jan Mayen in the west)
• Canary Islands threshold (it divides the Canary Basin into two unequal parts; between the North Atlantic Ridge in the west and the Canaries and the Democratic Arab Republic of the Sahara in Africa in the east)
• Cape Sill (separating the Atlantic and the Indies : between the Cape of Good Hope in South Africa in the north, the Agulhas Basin in the east, the Atlantic-Indian Southern Polar Basin in the south, the southern foothills of the South Atlantic Ridge in the southwest and the Cape Basin in the west and northwest)
• Cape Verde Sill (with Cape Verde ; between the Canary Basin in the north, Mauritania and Senegal in Africa in the east, the Cape Verde Basin in the south and the North Atlantic Ridge in the west)
• Liberia threshold (between the Sierra Leone Basin in the northwest, Liberia in the northeast, the Guinea Basin in the east and the northern end of the South Atlantic Ridge in the south)
• Mid-Atlantic Ridge (central ridge in the Atlantic, which divides the ocean into western and eastern halves; the Romanche Trench , which is up to 7,730 m deep, divides it at the equator into the North Atlantic and South Atlantic ridge )
• North Atlantic Ridge (the northern part of the Mid-Atlantic Ridge ; with Jan Mayen , Iceland and the Sankt-Peter-und-Sankt-Pauls-Felsen ; between Iceland or Jan Mayen in the north, Western Europe and North Africa and their upstream basins and thresholds in the east , the South Atlantic Ridge in the south and North and Central America as well as the northeast of South America and their upstream basins and thresholds in the west)
• Para wave (between the southern reaches of the North Atlantic Ridge in the north and east, the Brazilian Basin in the southeast, northeast Brazil in the southwest and the Guayana Basin in the northwest)
• Reykjanes Ridge (between Iceland in the northeast, the Iceland Basin in the east, the North Atlantic Ridge , to which the Reykjanes Ridge belongs, in the south and the Labrador Basin in the west)
• Rio Grande Sill (between the Brazilian Basin in the north, the South Atlantic Ridge in the east, the Argentine Basin in the south and South America in the west)
• Scotia Ridge (between the Falkland Ridge and a small southern extension ( to which the South Georgian threshold joins to the east ) of the Argentine Basin in the north, the South Sandwich Trench in the east, the South Antilles Basin in the south, Tierra del Fuego on the southern tip of South America in the west and the Falkland Islands in the northwest ; on the threshold lies South Georgia )
• Sierra Leone threshold (between Guinea and Sierra Leone in the northeast, the Sierra Leone basin in the southeast, the southern branch of the North Atlantic Ridge in the southwest and the Cape Verde Basin in the northwest)
• South Antilles Ridge (see Scotia Ridge )
• South Atlantic Ridge (the southern part of the Mid-Atlantic Ridge ; its southern end in a west-east direction is called the Atlantic-Indian Ridge ; with Ascension , Tristan da Cunha , Gough and Bouvet ; between Africa and its upstream basins and thresholds in the north and east, the Atlantic-Indian-Southern Polar Basin in the South and South America and its upstream basins and thresholds in the west)
• South Georgia Sill (between the Argentine Basin in the northwest, the South Atlantic Ridge in the northeast, the parallel South Sandwich Sill in the southeast and South Georgia in the southwest)
• South Sandwich Sill [between the parallel South Georgia Sill in the northwest, the South Atlantic Ridge in the northeast, the Atlantic-Indian-South Polar Basin in the southeast and south and the South Sandwich Islands behind the 8,264 m deep South Sandwich Trench in the west]
• Trindade threshold (with the islands of Trindade and Martim Vaz ; it divides the Brazilian Basin into two unevenly large parts; between the South Atlantic Ridge in the east and South America in the west)
• Walvis Ridge (between the Angola Basin in the northwest and north, Namibia in the Northeast, the Cape Basin in the east and south-east and the South Atlantic back in the southwest)

Indian Ocean

Thresholds or backs in the indicator are:

• Atlantic-Indian Ridge (see above under Atlantic )
• Bengali Sill (between the Bay of Bengal in the north, the Keeling Basin in the east, the Northwest Australian Basin in the southeast, the K XVIII Ridge in the south and the Central Indian Basin in the west)
• Carlsberg Ridge (see Northwest Indian Ridge )
• Crozetschwelle (with Crozet and Prince Edward Islands ; between the Madagascar Basin in the north, the Southwest Indian Basin in the northeast, the Atlantic-Indian-South Polar Basin in the south, the junction of the two aforementioned sea basins in the east, the Agulhas Basin in the west and the Natal Basin in the Northwest)
• Cape threshold (see above under Atlantic )
• Kerguelen-Gaußberg ridge (on this lie the Kerguelen ridge in the northwest and Heard Island in its center ; between the Central Indian Ridge in the north, the South Indian Ridge in the east, the Indian-South Polar Basin in the southeast, the Antarctic in the south, the Atlantic -Indian-South Polar Basin in the west, the Southwest Indian Basin in the northwest and the interface between the two last-mentioned sea basins in the west)
• K XVIII Ridge (between the Northwest Australian Basin in the north and northeast, the Southeast Indian Basin in the southeast and south, the junction of the two aforementioned lake basins in the east, the Central Indian Ridge in the west and the Central Indian Basin in the northwest)
• Macquarieschwelle (between the Sudaustralischen basin in the northwest and north, the Tasmanschwelle the east, the Antarctic in the south east, the Indian Südpolarbecken in the South and Southwest and the South Indian back in the West)
• Mascarene Ridge (with the Mascarene Mountains and the northeast end of the Seychelles ; between the Somali Basin in the north, the Central Indian Ridge in the east, the Madagascar Basin in the south and the Mascarene Basin in the west)
• Northwest Indian Ridge (also called Carlsberg Ridge ; between Socotra in the northwest, the Arabian Basin in the northeast and east, the Central Indian Sill in the south and the Somali Basin in the west)
• South Indian Ridge (between the Southeast Indian Basin in the north, the South Australian Basin in the northeast, the Macquaries Threshold in the east, the Indian Southern Polar Basin in the southeast and south, the Kerguelen-Gaußberg Ridge in the southwest and the Central Indian Ridge in the northwest)
• Tasman Threshold (separating the Indic and the Pacific ; between Tasmania in the north, the East Australian Basin in the northeast, Antarctica in the south, the Macquaries Threshold in the southwest and west and the South Australian Basin in the northwest)
• Tschagos Ridge (with Lakshadweep , Maldives and Tschagos ; between the west coast of India in the northeast, the Central Indian Basin in the east, the Central Indian Ridge in the south and the Arabian Basin in the west)
• Central Indian Ridge (with Nouvelle Amsterdam and St. Paul Island ; between Tschagos at the junction of the Northwest Indian Ridge and the Tschagos Ridge in the north, the Central Indian Basin in the east, the South Indian Ridge in the southeast, the Kerguelen-Gaußberg Ridge in the south, the Southwest Indian Basin in the southwest, the Madagascar Basin and the Mascarene Ridge with the Mascarene Mountains in the west and the Somali Basin in the northwest)

Mediterranean Sea

• Gibraltar Threshold (a threshold below sea level in the Strait of Gibraltar . It separates the Alborán Sea , the western part of the Mediterranean Sea , from the Gulf of Cádiz in the Atlantic Ocean)
• Mediterranean ridge (runs through almost the entire eastern Mediterranean from Calabria to Cyprus ; separates the Ionian Basin in the southwest from the Levantine Basin in the southeast; is bounded in the north by the Hellenic Trough )
• Sicily-Malta threshold (between Sicily and Malta or North Africa ; separates the western from the eastern part of the Mediterranean, which are connected here via the Strait of Sicily )

Pacific Ocean

Swellings or ridges in the Pacific are:

• Fanning Ridge (with Palmyra , Fanning and the Kiritimati ; between the North Pacific Basin in the north, west and southwest and the Central Pacific Basin in the east, southeast and south)
• Fiji back (with Fiji , between Fiji to the north, the Kermadec-Tonga back to the east and south, the Fiji Basin in the southwest and west)
• Galapagos Threshold (with the Galapagos Islands ; between the Central Pacific Basin in the northwest and west, Panama in the northeast, the northwest of South America in the east, the Peru Basin in the south and the East Pacific Ridge in the southwest)
• Hawaii Ridge (including Hawaii and Midway ; within the North Pacific Basin and southeast of the Northwest Pacific Ridge )
• Imperator Ridge (see Northwest Pacific Ridge )
• Hunterschwelle (divides the Fiji Basin into north and south Fiji Basin ; between New Caledonia in the west and Fiji in the east)
• Juan Fernandez back (with Juan Fernández Islands and San Félix , between Chile basin in the north, where up 8,064 m 'deep Atacama Trench off the coast of South America to the east, the eastern foothills of the Easter emerging in the south and the Peru Basin in the west and northwest )
• Juan de Fuca ridge west of Vancouver Island .
• Kermadec-Tonga Ridge (with Kermadec and Tonga ; between the extreme southwest foothills of the North Pacific Basin in the north, the South Pacific Basin behind the Kermadec Trench, which is up to 10,047 m deep, and the Tonga Trench, up to 10,882 m deep in the east, the North Island of New Zealand in the south, the Fiji basin in the southwest and the Fiji back to the west)
• Marcus Necker Ridge (with the Marcus and Wak Island ; between the North Pacific Basin in the north and east, the Mariana Basin in the south and the Mariana Trench in the west)
• Nazca Ridge (also called West Chilean Ridge ; with the Desventuradas Islands ; between the Peru Basin in the west and northwest, the Peru Rift in the north and the Chile Basin in the east and south)
• New Guinea Sill (this is in front of New Guinea to the south ; it divides the Caroline basin into two unequal parts; between the Carolines in the north and New Guinea in the south)
• New Hebrew Ridge (with Vanuatu and the Santa Cruz Islands ; between the southwest foothills of the North Pacific Basin in the north, the Fiji Basin in the east, the New Hebrew Basin in the south and southwest and the Solomon Islands in the northwest)
• New Caledonian Sill (with Norfolk Island ; between New Caledonia in the north, the Fiji Basin in the east, the North Island of New Zealand in the southeast and the parallel New Zealand Sill in the west; the southern part of this sill, which lies between the Norfolk Island and the North Island of New Zealand is called the Norfolk Sill )
• New Zealand Sill (between the coral basin in the northwest, the parallel New Caledonian threshold in the east, the South Island of New Zealand in the southeast and the East Australian Basin in the southwest and west)
• Northwest Pacific Ridge (also called the Imperator Ridge ; between the Aleutians behind the 7,678 m deep Aleutian Trench in the north, the North Pacific Basin in the east, the Hawaii Ridge in the southeast, the Marcus Necker Ridge in the south and the Northwest Pacific Basin in the west)
• Norfolk Sill (the southern part of the New Caledonian Sill - see there)
• East Pacific longitudinal sill (see East Pacific Ridge )
• East Pacific Ridge (also called the East Pacific Longitudinal Sill ; between the Galapagos Sill in the northeast, the Peru Basin in the east, the Easter Sill in the southeast, the South Pacific Basin in the west and the Central Pacific Basin in the northwest)
• South Honshu Ridge (with Izu Islands ; between the Japanese island of Honshū in the north, the northwest Pacific basin behind the 10,554 m deep Japan Rift in the east and the Philippines basin south, southwest and west)
• South Pacific Cross Sill (see South Pacific Ridge )
• Pacific-Antarctic Ridge (also South Pacific Cross Sill ; between the South Pacific Basin in the northwest and north, the East Pacific Ridge in the northeast, the Pacific South Polar Basin in the southeast and south and the Antarctic in the southwest)
• Tasman threshold (see above under Indic )
• West Chilean Ridge (see Nazca threshold )

Southern ocean

In the Southern Ocean , that is in the Southern Ocean and beyond the 60th southern latitude the foothills are both of these thresholds and back, heading north in the Atlantic , Indian Ocean and Pacific pass:

• Kerguelen-Gaußberg ridge (southeastern foothills; see above under Indian Ocean )
• South Pacific Ridge (southwest part; see above under Pacific Ocean )

See also

• Basin (geology)
• Depth sounder / Lotung
• Sea depth
• oceanography

swell

1. ^ Haack Atlas Weltmeer. VEB Hermann Haack Geographical-Cartographic Institute Gotha 1989, p. 10
2. ↑ Alfred Wegener Institute for the Amore Expedition ( Memento of the original of September 27, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.