The Kula Plate was an oceanic tectonic plate under the northern Pacific Ocean south of the Near Islands segment of the Aleutian Islands. It has been subducted under the North American Plate at the Aleutian Trench, being replaced by the Pacific Plate; the name Kula is from a Tlingit language word meaning "all gone". As the name suggests, the Kula Plate was subducted around 48 Ma and today only a slab in the mantle under the Bering Sea remains; the Kula Plate began subducting under the Pacific Northwest region of North America during the Late Cretaceous period much like the Pacific Plate does, supporting a large volcanic arc system from northern Washington to southwestern Yukon called the Coast Range Arc. There was a triple junction of three ridges between the Kula Plate to the north, the Pacific Plate to the west and the Farallon Plate to the east; the Kula Plate was subducted under the North American Plate at a steep angle, so that the Canadian Rockies are composed of thrusted sedimentary sheets with little contribution of continental uplift, while the American Rockies are characterized by significant continental uplift in response to the shallow subduction of the Farallon Plate.
About 55 million years ago, the Kula Plate began an more northerly motion. Riding on the Kula Plate was the Pacific Rim Terrane consisting of volcanic and sedimentary rocks, it was scraped off and plastered against the continental margin, forming what is today Vancouver Island. By 40 million years ago, the compressional force of the Kula Plate ceased; the existence of the Kula Plate was inferred from the westward bend in the alternating pattern of magnetic anomalies in the Pacific Plate. Farallon Plate Kula-Farallon Ridge Pacific-Kula Ridge Izanagi Plate Reconstruction of the Kula Plate Kula Plate in the area of the present Northwestern United States Kula plate when it separates from the Farallon plate
The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which rises through a narrow slope into the shallower water above the continental shelves; the Bering Sea is separated from the Gulf of Alaska by the Alaska Peninsula. It covers over 2,000,000 square kilometers and is bordered on the east and northeast by Alaska, on the west by Russian Far East and the Kamchatka Peninsula, on the south by the Alaska Peninsula and the Aleutian Islands and on the far north by the Bering Strait, which connects the Bering Sea to the Arctic Ocean's Chukchi Sea. Bristol Bay is the portion of the Bering Sea which separates the Alaska Peninsula from mainland Alaska; the Bering Sea is named for Vitus Bering, a Danish navigator in Russian service, who in 1728 was the first European to systematically explore it, sailing from the Pacific Ocean northward to the Arctic Ocean. The Bering Sea ecosystem includes resources within the jurisdiction of the United States and Russia, as well as international waters in the middle of the sea.
The interaction between currents, sea ice, weather makes for a vigorous and productive ecosystem. Most scientists believe that during the most recent ice age, sea level was low enough to allow humans to migrate east on foot from Asia to North America across what is now the Bering Strait. Other animals including megafauna migrated in both directions; this is referred to as the "Bering land bridge" and is believed by most, though not all scientists, to be the first point of entry of humans into the Americas. There is a small portion of the Kula Plate in the Bering Sea; the Kula Plate is an ancient tectonic plate. On 18 December 2018, a large meteor exploded above the Bering Sea; the space rock exploded with 10 times the energy released by the Hiroshima atomic bomb. The International Hydrographic Organization defines the limits of the Bering Sea as follows: On the North; the Southern limit of the Chuckchi Sea. On the South. A line running from Kabuch Point in the Alaskan Peninsula, through the Aleutian Islands to the South extremes of the Komandorski Islands and on to Cape Kamchatka in such a way that all the narrow waters between Alaska and Kamchatka are included in the Bering Sea.
Islands of the Bering Sea include: Pribilof Islands, including St. Paul Island Komandorski Islands, including Bering Island St. Lawrence Island Diomede Islands King Island St. Matthew Island Karaginsky Island Nunivak Island Sledge Island Hagemeister Island Regions of the Bering Sea include: Bering Strait Bristol Bay Gulf of Anadyr Norton SoundThe Bering Sea contains 16 submarine canyons including the largest submarine canyon in the world, Zhemchug Canyon; the Bering Sea shelf break is the dominant driver of primary productivity in the Bering Sea. This zone, where the shallower continental shelf drops off into the North Aleutians Basin is known as the "Greenbelt". Nutrient upwelling from the cold waters of the Aleutian basin flowing up the slope and mixing with shallower waters of the shelf provide for constant production of phytoplankton; the second driver of productivity in the Bering Sea is seasonal sea ice that, in part, triggers the spring phytoplankton bloom. Seasonal melting of sea ice causes an influx of lower salinity water into the middle and other shelf areas, causing stratification and hydrographic effects which influence productivity.
In addition to the hydrographic and productivity influence of melting sea ice, the ice itself provides an attachment substrate for the growth of algae as well as interstitial ice algae. Some evidence suggests that great changes to the Bering Sea ecosystem have occurred. Warm water conditions in the summer of 1997 resulted in a massive bloom of low energy coccolithophorid phytoplankton. A long record of carbon isotopes, reflective of primary production trends of the Bering Sea, exists from historical samples of bowhead whale baleen. Trends in carbon isotope ratios in whale baleen samples suggest that a 30–40% decline in average seasonal primary productivity has occurred over the last 50 years; the implication is that the carrying capacity of the Bering Sea is much lower now than it has been in the past. The sea supports many whale species including the beluga, humpback whale, bowhead whale, gray whale and blue whale, the vulnerable sperm whale, the endangered fin whale, sei whale and the rarest in the world, the North Pacific right whale.
Other marine mammals include walrus, Steller sea lion, northern fur seal and polar bear. The Bering Sea is important to the seabirds of the world. Over 30 species of seabirds and 20 million individuals breed in the Bering Sea region. Seabird species include tufted puffins, the endangered short-tailed albatross, spectacled eider, red-legged kittiwakes. Many of these species are unique to the area, which provides productive foraging habitat along the shelf edge and in other nutrient-rich upwelling regions, such as the Pribilof and Pervenets canyons; the Bering Sea is home to colonies of crested auklets, with upwards of a million individuals. Two Bering Sea species, the Steller's sea cow and spectacled cormorant, are extinct because of overexploitation by man. In addition, a small subspecies of Canada goose, the Bering Canada goose is extinct due to overhunting and introduction of rats to their breeding islands; the Bering Sea supports many species of fish. Some species of fish support valuable commercial fisheries.
Commercial fish species include 6 species of Pacific salmon
A submarine canyon is a steep-sided valley cut into the seabed of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, having canyon wall heights of up to 5 km, from canyon floor to canyon rim, as with the Great Bahama Canyon. Just as above-sea-level canyons serve as channels for the flow of water across land, submarine canyons serve as channels for the flow of turbidity currents across the seafloor. Turbidity currents are flows of dense, sediment laden waters that are supplied by rivers, or generated on the seabed by storms, submarine landslides and other soil disturbances. Turbidity currents travel down slope at great speed, eroding the continental slope and depositing sediment onto the abyssal plain, where the particles settle out. About 3% of submarine canyons include shelf valleys that have cut transversely across continental shelves, which begin with their upstream ends in alignment with and sometimes within the mouths of large rivers, such as the Congo River and the Hudson Canyon.
About 28.5% of submarine canyons cut back into the edge of the continental shelf, whereas the majority of submarine canyons have not managed at all to cut across their continental shelves, having their upstream beginnings or "heads" on the continental slope, below the edge of continental shelves. The formation of submarine canyons is believed to occur as the result of at least two main process: 1) erosion by turbidity current erosion. While at first glance, the erosion patterns of submarine canyons may appear to mimic those of river-canyons on land, due to the markedly different erosion processes that have been found to take place underwater at the soil/ water interface, several notably different erosion patterns have been observed in the formation of typical submarine canyons. Many canyons have been found at depths greater than 2 km below sea level; some may extend seawards across continental shelves for hundreds of kilometres before reaching the abyssal plain. Ancient examples have been found in rocks dating back to the Neoproterozoic.
Turbidites are deposited at the downstream ends of canyons, building an abyssal fan. Submarine canyons are more common on the steep slopes found on active margins compared to those on the gentler slopes found on passive margins, they show erosion from unlithified sediment to crystalline rock. Canyons are steeper, more dendritic and more spaced on active than on passive continental margins; the walls are very steep and can be near vertical. The walls are subject to slumping. There are an estimated 9,477 submarine canyons on Earth, covering about 11% of the continental slope. Avilés Canyon, off the coast of Asturias, reaches abyssal depths of more than 4,500 m. Amazon Canyon, extending from the Amazon River Baltimore and Wilmington Canyons, East Coast of Maryland and Delaware States Bering Canyon, in the Bering Sea Congo Canyon, the largest river canyon, extending from the Congo River, is 800 km long, 1,200 m deep. Hudson Canyon, extending from the Hudson River Ganges Canyon, extending from the Ganges Indus Canyon, extending from the Indus River Kaikoura Canyon, extending offshore from the Kaikoura Peninsula, New Zealand La Jolla and Scripps Canyon, off the coast of La Jolla, southern California Monterey Canyon, off the coast of central California Nazaré Canyon, off the coast of Portugal Pribilof Canyon, in the Bering Sea Whittard Canyon, Atlantic Ocean off southwest Ireland Zhemchug Canyon the largest submarine canyon in the world, in the Bering sea Different mechanisms have been proposed for the formation of submarine canyons.
Their primary causes have been subject to debate since the early 1930s. An early and obvious theory was that the canyons present today were carved during glacial times, when sea level was about 125 meters below present sea level, rivers flowed to the edge of the continental shelf. However, while many canyons are found offshore from major rivers, subaerial river erosion cannot have been active to the water depths as great as 3000 meters where canyons have been mapped, as it is well established that sea levels did not fall to those depths; the major mechanism of canyon erosion is thought to be underwater landslides. Turbidity currents are dense, sediment-laden currents which flow downslope when an unstable mass of sediment, deposited on the upper slope fails triggered by earthquakes. There is a spectrum of turbidity- or density-current types ranging from "muddy water" to massive mudflow, evidence of both these end members can be observed in deposits associated with the deeper parts of submarine canyons and channels, such as lobate deposits and levees along channels.
Mass wasting and submarine landslides are forms of slope failures observed in submarine canyons. Mass wasting is the term used for the smaller action of material moving downhill. Slumping is used for rotational movement of masses on a hillside. Landslides, or slides comprise the detachment and displacement of sediment masses, it is now understood that many mechanisms of submarine canyon creation have had effect to greater or lesser degree in different places within the same canyon, or at different times during a canyon's development. However, if a primary mechanism must be selected, the downslope lineal morphology of canyons and channels and the transportation of excavated or loose materials of the continental slope over extensive distances require that various kinds o
Zhemchug Canyon is an underwater canyon located in the middle of the Bering Sea. This submarine canyon is tied for widest canyon in the ocean, it has a vertical relief of 8,530 feet or 2,600 meters dropping from the shallow shelf of the Bering Sea to the depths of the Aleutian Basin. Zhemchug Canyon is deeper than the Grand Canyon, 6,093 feet or 1,857 meters deep, it has two main branches, each larger than typical continental margin canyons such as the Monterey Canyon. What makes the Zhemchug Canyon the world's largest is not only its great depth, but its immense cross-sectional and drainage area, volume. In 2016, Michelle Ridgeway explored the canyon piloting an eight-foot submarine in an expedition sponsored by Greenpeace, she reached a shelf at a depth of 1,757 feet or 536 meters, that is, a third of a mile below the surface. Zhemchug Canyon is important habitat for many species of ocean wildlife; the endangered short-tailed albatross congregates to feed over the surface waters of the canyon.
Marine mammals such as northern fur seals feed in the canyon as do dolphins and many species of whales. Habitat-forming invertebrates such as bubblegum coral, bamboo coral, soft corals, Hexactinellid sponges, other sponges have been identified during trawl surveys in the canyon, it is where the opilio bairdi crab can be found. Submarine canyons of the Bering Sea Bering Sea topics
Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone, they are the principal way. Island arcs can either be inactive based on their seismicity and presence of volcanoes. Active arcs are ridges of recent volcanoes with an associated deep seismic zone, they possess a distinct curved form, a chain of active or extinct volcanoes, a deep-sea trench, a large negative Bouguer anomaly on the convex side of the volcanic arc. The small positive gravity anomaly associated with volcanic arcs has been interpreted by many authors as due to the presence of dense volcanic rocks beneath the arc. While inactive arcs are a chain of islands which contains older volcanic and volcaniclastic rocks; the curved shape of many volcanic chains and the angle of the descending lithosphere are related. If the oceanic part of the plate is represented by the ocean floor on the convex side of the arc, if the zone of flexing occurs beneath the submarine trench the deflected part of the plate coincides with the Benioff zone beneath most arcs.
Most modern island arcs are near the continental margins. However, no direct evidence from within the arcs shows that they have always existed at their present position with respect to the continents. Though, evidence from some continental margins suggests that some arcs may have migrated toward the continents during the late Mesozoic or early Cenozoic; the movement of the island arcs towards the continent could be possible if, at some point, the ancient Benioff zones dipped toward the present ocean rather than toward the continent, as in most arcs today. This will have resulted in the loss of ocean floor between the arc and the continent, in the migration of the arc during spreading episodes; the fracture zones in which some active island arcs terminate may be interpreted in terms of plate tectonics as resulting from movement along transform faults, which are plate margins where the crust is neither being consumed nor generated. Thus the present location of these inactive island chains is due to the present pattern of lithospheric plates.
However, their volcanic history, which indicates that they are fragments of older island arcs, is not related to the present plate pattern and may be due to differences in position of plate margins in the past. Understanding the source of heat that causes the melting of the mantle was a contentious problem. Researchers believed. However, this is unlikely because the viscosity of the asthenosphere decreases with increasing temperature, at the temperatures required for partial fusion, the asthenosphere would have such a low viscosity that shear melting could not occur, it is now believed. It has been shown that the amount of water present in the down-going slab is related to the melting temperature of the mantle; the greater the amount of water present, the more the melting temperature of the mantle is reduced. This water is released during the transformation of minerals as pressure increases, with the mineral carrying the most water being serpentinite; these metamorphic mineral reactions cause the dehydration of the upper part of the slab as the hydrated slab sinks.
Heat is transferred to it from the surrounding asthenosphere. As heat is transferred to the slab, temperature gradients are established such that the asthenosphere in the vicinity of the slab becomes cooler and more viscous than surrounding areas near the upper part of the slab; this more viscous asthenosphere is dragged down with the slab causing less viscous mantle to flow in behind it. It is the interaction of this down-welling mantle with aqueous fluids rising from the sinking slab, thought to produce partial melting of the mantle as it crosses its wet solidus. In addition, some melts may result from the up-welling of hot mantle material within the mantle wedge. If hot material rises enough so that little heat is lost, the reduction in pressure may cause pressure release or decompression partial melting. On the subducting side of the island arc is a deep and narrow oceanic trench, the trace at the Earth's surface of the boundary between the down-going and overriding plates; this trench is created by the downward gravitational pull of the dense subducting plate on the leading edge of the plate.
Multiple earthquakes occur along this subduction boundary with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Benioff zone. Island arcs can be formed in intra-oceanic settings, or from the fragments of continental crust that have migrated away from an adjacent continental land mass or at subduction-related volcanoes active at the margins of continents. Below are some of the generalized features present in most island arcs. Fore-arc: This region comprises the trench, the accretionary prism, the fore-arc basin. A bump from the trench in the oceanward side of the system is present; the fore-arc basin forms between the island arc. Trenches: These are the deepest features of ocean basins, they are formed by developing on the ocean side of island arcs. Back-arc basin: They are referred to as marginal sea
The Aleutian Islands called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large volcanic islands and 55 smaller ones belonging to both the U. S. state of Alaska and the Russian federal subject of Kamchatka Krai. They form part of the Aleutian Arc in the Northern Pacific Ocean, occupying an area of 6,821 sq mi and extending about 1,200 mi westward from the Alaska Peninsula toward the Kamchatka Peninsula in Russia, mark a dividing line between the Bering Sea to the north and the Pacific Ocean to the south. Crossing longitude 180°, at which point east and west longitude end, the archipelago contains both the westernmost part of the United States by longitude and the easternmost by longitude; the westernmost U. S. island in real terms, however, is Attu Island. While nearly all the archipelago is part of Alaska and is considered as being in the "Alaskan Bush", at the extreme western end, the small, geologically related Commander Islands belong to Russia.
The islands, with their 57 volcanoes, form the northernmost part of the Pacific Ring of Fire. Physiographically, they are a distinct section of the larger Pacific Border province, which in turn is part of the larger Pacific Mountain System physiographic division; these Islands are most known for the battles and skirmishes that occurred there during the Aleutian Islands Campaign of World War II. It was one of only two attacks on the United States during that war. Motion between the Kula Plate and the North American Plate along the margin of the Bering Shelf ended in the early Eocene; the Aleutian Basin, the ocean floor north of the Aleutian arc, is the remainder of the Kula Plate that got trapped when volcanism and subduction jumped south to its current location at c. 56 Ma. The Aleutian island arc formed in the Early Eocene when the subduction of the Pacific Plate under the North American Plate began; the arc is made of separate blocks. The basement underlying the islands is made of three stratigraphic units: an Eocene layer of volcanic rock, an Oligocene—Miocene layer of marine sedimentary rock, a Pliocene—Quaternary layer of sedimentary and igneous rock.
The islands, known before 1867 as the Catherine Archipelago, comprise five groups the Fox Islands Islands of Four Mountains Andreanof Islands Rat Islands, Near IslandsAll five are located between 51° and 55° N latitude and 172° E and 163° W longitude. The largest islands in the Aleutians are Attu, Unalaska and Unimak in the Fox Islands; the largest of those is Unimak Island, with an area of 1,571.41 mi2, followed by Unalaska Island, the only other Aleutian Island with an area over 1,000 square miles. The axis of the archipelago near the mainland of Alaska has a southwest trend, but at Tanaga Island its direction changes to the northwest; this change of direction corresponds to a curve in the line of volcanic fissures that have contributed their products to the building of the islands. Such curved chains are repeated about the Pacific Ocean in the Kuril Islands, the Japanese chain, in the Philippines. All these island arcs are at the edge of the Pacific Plate and experience much seismic activity, but are still habitable.
The general elevation is least in the western. The island chain is a western continuation of the Aleutian Range on the mainland; the great majority of the islands bear evident marks of volcanic origin, there are numerous volcanic cones on the north side of the chain, some of them active. The coasts are rocky and surf-worn, the approaches are exceedingly dangerous, the land rising from the coasts to steep, bold mountains; these volcanic islands reach heights of 6,200 feet. Makushin Volcano located on Unalaska Island, is not quite visible from within the town of Unalaska, though the steam rising from its cone is visible on a clear day. Residents of Unalaska need only to climb one of the smaller hills in the area, such as Pyramid Peak or Mt. Newhall, to get a good look at the snow-covered cone; the volcanic Bogoslof and Fire Islands, which rose from the sea in 1796 and 1883 lie about 30 miles west of Unalaska Bay. In 1906, a new volcanic cone rose between the islets of Bogoslof and Grewingk, near Unalaska, followed by another in 1907.
These cones were nearly demolished by an explosive eruption on September 1, 1907. Newly found information in 2017, the volcanic cone erupted sending ash and ice particles 30,000 feet in the air; the Aleutians seen from space The climate of the islands is oceanic, with moderate and uniform temperatures and heavy rainfall. Fogs are constant. Summer weather is much cooler than Southeast Alaska, but the winter temperature of the islands and of the Alaska Panhandle is nearly the same. According to the Köppen climate classification system, the area southwest of 53.5°N 167.0°W / 53.5.
Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced to sink due to gravity into the mantle. Regions where this process occurs are known as subduction zones. Rates of subduction are in centimeters per year, with the average rate of convergence being two to eight centimeters per year along most plate boundaries. Plates include continental crust. Stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere; that is, the subducted lithosphere is always oceanic while the overriding lithosphere may or may not be oceanic. Subduction zones are sites that have a high rate of volcanism and earthquakes. Furthermore, subduction zones develop belts of deformation and metamorphism in the subducting crust, whose exhumation is part of orogeny and leads to mountain building in addition to collisional thickening.
Subduction zones are sites of gravitational sinking of Earth's lithosphere. Subduction zones exist at convergent plate boundaries where one plate of oceanic lithosphere converges with another plate; the descending slab, the subducting plate, is over-ridden by the leading edge of the other plate. The slab sinks at an angle of twenty-five to forty-five degrees to Earth's surface; this sinking is driven by the temperature difference between the subducting oceanic lithosphere and the surrounding mantle asthenosphere, as the colder oceanic lithosphere has, on average, a greater density. At a depth of greater than 60 kilometers, the basalt of the oceanic crust is converted to a metamorphic rock called eclogite. At that point, the density of the oceanic crust provides additional negative buoyancy, it is at subduction zones that Earth's lithosphere, oceanic crust and continental crust, sedimentary layers and some trapped water are recycled into the deep mantle. Earth is so far the only planet. Subduction is the driving force behind plate tectonics, without it, plate tectonics could not occur.
Oceanic subduction zones dive down into the mantle beneath 55,000 kilometers of convergent plate margins equal to the cumulative 60,000 kilometers of mid-ocean ridges. Subduction zones burrow but are imperfectly camouflaged, geophysics and geochemistry can be used to study them. Not the shallowest portions of subduction zones are known best. Subduction zones are asymmetric for the first several hundred kilometers of their descent, they start to go down at oceanic trenches. Their descents are marked by inclined zones of earthquakes that dip away from the trench beneath the volcanoes and extend down to the 660-kilometer discontinuity. Subduction zones are defined by the inclined array of earthquakes known as the Wadati–Benioff zone after the two scientists who first identified this distinctive aspect. Subduction zone earthquakes occur at greater depths than elsewhere on Earth; the subducting basalt and sediment are rich in hydrous minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as the subducting slab bends downward.
During the transition from basalt to eclogite, these hydrous materials break down, producing copious quantities of water, which at such great pressure and temperature exists as a supercritical fluid. The supercritical water, hot and more buoyant than the surrounding rock, rises into the overlying mantle where it lowers the pressure in the mantle rock to the point of actual melting, generating magma; the magmas, in turn, rise. The mantle-derived magmas can continue to rise to Earth's surface, resulting in a volcanic eruption; the chemical composition of the erupting lava depends upon the degree to which the mantle-derived basalt interacts with Earth's crust and/or undergoes fractional crystallization. Above subduction zones, volcanoes exist in long chains called volcanic arcs. Volcanoes that exist along arcs tend to produce dangerous eruptions because they are rich in water and tend to be explosive. Krakatoa, Nevado del Ruiz, Mount Vesuvius are all examples of arc volcanoes. Arcs are known to be associated with precious metals such as gold and copper believed to be carried by water and concentrated in and around their host volcanoes in rock called "ore".
Although the process of subduction as it occurs today is well understood, its origin remains a matter of discussion and continuing study. Subduction initiation can occur spontaneously if denser oceanic lithosphere is able to founder and sink beneath adjacent oceanic or continental lithosphere. Both models can yield self-sustaining subduction zones, as oceanic crust is metamorphosed at great depth and becomes denser than the surrounding mantle rocks. Results from numerical models favor induced subduction initiation for most modern subduction zones, supported by geologic studies, but other analogue modeling shows the possibility of spontaneous subduction from inherent density differences between two plates at passiv