The Bouvet Triple Junction is a geologic

triple junction A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can b ...

of three

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ...

plates located on the seafloor of the South

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

. It is named after

Bouvet Island Bouvet Island ( ; or ''Bouvetøyen'') is an island claimed by Norway, and declared an uninhabited protected nature reserve. It is a subantarctic volcanic island, situated in the South Atlantic Ocean at the southern end of the Mid-Atlantic Ri ...

, which lies 275 kilometers to the east. The three plates which meet here are the

South American Plate The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-A ...

, the

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plat ...

, and the

Antarctic Plate The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau, and some remote islands in the Southern Ocean and other surrounding oceans. After breakup from Gondwana (the southern part of the superconti ...

. The Bouvet Triple Junction is an R-R-R type, that is, the three plate boundaries which meet here are

mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...

s: the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North Ame ...

(MAR), the

Southwest Indian Ridge The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...

(SWIR), and the South American-Antarctic Ridge (SAAR).

Transform valleys

There are two prominent transform valleys in the area: Conrad transform and Bouvet transform. Conrad transform is named after . Bouvet Island is the highest point on the southern wall of the Bouvet transform.

Development

Up to 10 million years ago the Mid-Atlantic Ridge and the two deep transform valleys of Conrad and Bouvet met in one point. Thus the triple junction was of the ridge-fault-fault (RFF) type. Conrad transform, stretching to the west, connected the end of the Mid-Atlantic Ridge to the South American-Antarctic Ridge. Bouvet transform linked it to the Southwest Indian Ridge on the eastern side. Currently Conrad transform and Bouvet transform are no longer connected to each other. The Mid-Atlantic Ridge is retreating northward, at a rate of . New spreading sections of the South American-Antarctic Ridge and the Southwest Indian Ridge are growing northward from the eastern end of Conrad transform and the western end of Bouvet transform respectively, striving for the shifting triple point. Thus the Mid-Atlantic Ridge is opening like a

zipper A zipper, zip, fly, or zip fastener, formerly known as a clasp locker, is a commonly used device for binding together two edges of textile, fabric or other flexible material. Used in clothing (e.g. jackets and jeans), luggage and other Bag, ba ...

. The new spreading sections are somewhat unusual: * One new spreading section of the South American-Antarctic Ridge is not perpendicular to Conrad fault, violating the perpendicular pattern of alternating spreading ridges and transform faults generally seen on slowly spreading oceanic ridges. * The new part of the Southwest Indian Ridge is masked by the recently formed Spiess Seamount. This volcanic seamount is the highest point in the area after Bouvet Island. Spiess Seamount was named after

captain Captain is a title, an appellative for the commanding officer of a military unit; the supreme leader of a navy ship, merchant ship, aeroplane, spacecraft, or other vessel; or the commander of a port, fire or police department, election precinct, e ...

Fritz Spieß of the

German Meteor expedition The German Meteor expedition (German: ''Deutsche Atlantik Expedition'') was an oceanographic expedition that explored the South Atlantic ocean from the equatorial region to Antarctica in 1925–1927. Depth soundings, water temperature studies, wat ...

of 1926.

References

* * {{Coord, 54, 17, 30, S, 1, 5, 0, W, display=title Plate tectonics Triple junctions Bouvet Island Mid-Atlantic Ridge