Misplaced Pages

#547452

44-411: It was formed during the last 1.1 million years by the effects of erosion associated with repeated ice stream activity. The trench is not a subduction -related oceanic trench , where one tectonic plate is being forced under another. The Norwegian Trench was created by fluvial erosion processes during the later Tertiary age. Pleistocene glaciers and ice sheets further deepened the trench. During

88-653: A country have become erodible. For example, on the Madagascar high central plateau , which constitutes approximately ten percent of that country's land area, most of the land area is devegetated, and gullies have eroded into the underlying soil to form distinctive gulleys called lavakas . These are typically 40 meters (130 ft) wide, 80 meters (260 ft) long and 15 meters (49 ft) deep. Some areas have as many as 150 lavakas/square kilometer, and lavakas may account for 84% of all sediments carried off by rivers. This siltation results in discoloration of rivers to

132-468: A dark red brown color and leads to fish kills. In addition, sedimentation of river basins implies sediment management and siltation costs.The cost of removing an estimated 135 million m of accumulated sediments due to water erosion only is likely exceeding 2.3 billion euro (€) annually in the EU and UK, with large regional differences between countries. Erosion is also an issue in areas of modern farming, where

176-432: A grain, such as pits, fractures, ridges, and scratches. These are most commonly evaluated on quartz grains, because these retain their surface markings for long periods of time. Surface texture varies from polished to frosted, and can reveal the history of transport of the grain; for example, frosted grains are particularly characteristic of aeolian sediments, transported by wind. Evaluation of these features often requires

220-458: A higher density and viscosity . In typical rivers the largest carried sediment is of sand and gravel size, but larger floods can carry cobbles and even boulders . Wind results in the transportation of fine sediment and the formation of sand dune fields and soils from airborne dust. Glaciers carry a wide range of sediment sizes, and deposit it in moraines . The overall balance between sediment in transport and sediment being deposited on

264-426: A hydrodynamic sorting process within the marine environment leading to a seaward fining of sediment grain size. One cause of high sediment loads is slash and burn and shifting cultivation of tropical forests. When the ground surface is stripped of vegetation and then seared of all living organisms, the upper soils are vulnerable to both wind and water erosion. In a number of regions of the earth, entire sectors of

308-470: A result, can cause exposed sediment to become more susceptible to erosion and delivery to the marine environment during rainfall events. Sediment can negatively affect corals in many ways, such as by physically smothering them, abrading their surfaces, causing corals to expend energy during sediment removal, and causing algal blooms that can ultimately lead to less space on the seafloor where juvenile corals (polyps) can settle. When sediments are introduced into

352-404: Is a region of fast-moving ice within an ice sheet . It is a type of glacier , a body of ice that moves under its own weight. They can move upwards of 1,000 metres (3,300 ft) a year, and can be up to 50 kilometres (31 mi) in width, and hundreds of kilometers in length. They tend to be about 2 km (1.2 mi) deep at the thickest, and constitute the majority of the ice that leaves

396-475: Is almost negligible. As ice streams diminish in size, the pressure they exert on surrounding features like glaciers reduces, allowing the glacier that feeds into the sea to speed up and discharge more quickly, rising sea level. This rise in sea level affects both topography and bathymetry in the regions directly affected by the ice stream in question. As a result of this rise in sea level, albeit slow and almost minute in short scales but large over longer scales,

440-460: Is bedrock, and not made of sediments, the speed will decrease. The bedrock acts to slow down the ice stream as it incises and deforms it. Flow velocity of the ice stream is not entirely constant, but in short time scales of days to weeks, it can be treated as such, over long scales, however, it is variable, depending on how the conditions of thickness, temperature, water accumulation, stresses, and base material have changed. The Antarctic Ice Sheet

484-476: Is drained to the sea by several ice streams. The largest in East Antarctica is Lambert Glacier . In West Antarctica the large Pine Island and Thwaites Glaciers are currently the most out of balance, with a total net mass loss of 85 gigatonnes (84 billion long tons; 94 billion short tons) per year measured in 2006. Antarctica has many ice streams that carry billions of tons of ice to

SECTION 10

#1732766199548

528-551: Is expected to be delivered to the outlet of the river. The sediment transfer and deposition can be modelled with sediment distribution models such as WaTEM/SEDEM. In Europe, according to WaTEM/SEDEM model estimates the Sediment Delivery Ratio is about 15%. Watershed development near coral reefs is a primary cause of sediment-related coral stress. The stripping of natural vegetation in the watershed for development exposes soil to increased wind and rainfall and, as

572-604: Is lost through them. While East Antarctica is generally stable, ice loss in West Antarctica has increased by 59% in the past 10 years and by 140% in the Antarctic peninsula . Ice streams control much of the ice sheet mass budget as they dictate the amount of discharge that comes off an ice sheet. Geomorphic features such as bathymetric troughs indicate where paleo-ice streams in Antarctica extended during

616-581: Is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "boulder". The shape of particles can be defined in terms of three parameters. The form is the overall shape of the particle, with common descriptions being spherical, platy, or rodlike. The roundness is a measure of how sharp grain corners are. This varies from well-rounded grains with smooth corners and edges to poorly rounded grains with sharp corners and edges. Finally, surface texture describes small-scale features such as scratches, pits, or ridges on

660-421: Is one of the reasons why it is so difficult for oceans to freeze or evaporate. Water is also a poor conductor of heat, so increased thickness will not only increase the amount of heat that can be retained, but also make more energy required for heat to be lost. In addition to thickness, water, and stresses, sediment and bedrock play a key role in the rate at which ice streams drain. If the underlying sediment

704-484: Is that thicker ice results in faster velocity. As the thicker an ice stream is, the greater the driving stress at the bed, and thus the greater the velocity. In addition to driving stress, ice streams have better insulation as the thickness of ice increases, due to it retaining higher temperatures better, it can increase the rate of deformation, as well as basal sliding. As a substance's volume increases, it requires more energy per unit volume to raise its temperature, which

748-417: Is too porous , allowing for too much water to seep into it, and therefore become saturated , it will be incapable of supporting the shear stress the ice stream places on the bed. The best type of sediment for increased speed of drainage is soft, deformable sediment, that allows the ice stream to flow over the combination of sediment and till , while supporting against shear stress . If the underlying surface

792-632: The Greenland ice sheet into the sea include Helheim Glacier , Jakobshavn Isbræ and Kangerdlugssuaq Glacier . With significantly more surface melt, only 50% of ice mass is lost through ice streams in Greenland, but they still are one of the primary modes of ice loss. the Northeast Greenland Ice Stream, at 600 km (370 mi) long, drains roughly 12% of the entire ice sheet through three outlet glaciers. Earlier in

836-568: The Last Glacial Maximum (LGM). Analysis of landforms diagnostic of paleo-ice streams, revealed considerable asynchronicity in individual ice stream retreat histories. This notion is important when considering how the underlying geomorphology of ice streams control at what rate and how they retreat. Furthermore, this reinforces the importance of internal factors such as bed characteristic, slope , and drainage basin size in determining ice stream dynamics. Ice streams that drain

880-533: The Holocene, the ice stream system of northeast Greenland reached much farther into Greenland's interior compared to the present day. The northeast Greenland ice stream behaves similarly to the Ross ice streams of West Antarctica with fast flow and a weak bed with low driving stresses. The basal shear stress balances the driving stress for several hundred kilometers in the center of the ice stream. Further upstream,

924-638: The Skagerrak and Oslo areas respectively, and deformed glacial tills found on the coast of Jæren provide the main onshore evidence for the Norwegian Channel Ice Stream. The Norwegian current generally flows northeasterly along the Norwegian trench. The depth of the trench, along with density differences between Norwegian current water and the adjacent Atlantic Water, results in large-scale eddies. The Norwegian trench region in

SECTION 20

#1732766199548

968-559: The Skagerrak is a biologically productive zone, as upwelling of North Atlantic water in the Skagerrak provides an input of nutrients. After World War II , chemical weapons were dumped in the Norwegian Channel , when 36 ships were sunk there by allies with approval from the Norwegian authorities. The trench has provided an obstacle for oil and gas pipelines. 60°00′N 4°00′E  /  60.0°N 4.0°E  / 60.0; 4.0 Ice stream An ice stream

1012-600: The bed is given by the Exner equation . This expression states that the rate of increase in bed elevation due to deposition is proportional to the amount of sediment that falls out of the flow. This equation is important in that changes in the power of the flow change the ability of the flow to carry sediment, and this is reflected in the patterns of erosion and deposition observed throughout a stream. This can be localized, and simply due to small obstacles; examples are scour holes behind boulders, where flow accelerates, and deposition on

1056-579: The body of water. Terrigenous material is often supplied by nearby rivers and streams or reworked marine sediment (e.g. sand ). In the mid-ocean, the exoskeletons of dead organisms are primarily responsible for sediment accumulation. Deposited sediments are the source of sedimentary rocks , which can contain fossils of the inhabitants of the body of water that were, upon death, covered by accumulating sediment. Lake bed sediments that have not solidified into rock can be used to determine past climatic conditions. The major areas for deposition of sediments in

1100-417: The coastal regions of the ocean, the proportion of land, marine, and organic-derived sediment that characterizes the seafloor near sources of sediment output is altered. In addition, because the source of sediment (i.e., land, ocean, or organically) is often correlated with how coarse or fine sediment grain sizes that characterize an area are on average, grain size distribution of sediment will shift according to

1144-405: The direction and magnitude of ice streams. Ice streams have various impacts on the surrounding event. The most obvious one is the development of large topographic lows and valleys after an ice stream has been completely drained from the ice sheet itself. The topographic lows are formed by glacial erosion as the stream carves through the underlain material, eroding it and pushing sediment into

1188-422: The edges and corners of particle are. Complex mathematical formulas have been devised for its precise measurement, but these are difficult to apply, and most geologists estimate roundness from comparison charts. Common descriptive terms range from very angular to angular to subangular to subrounded to rounded to very rounded, with increasing degree of roundness. Surface texture describes the small-scale features of

1232-510: The flow. In geography and geology , fluvial sediment processes or fluvial sediment transport are associated with rivers and streams and the deposits and landforms created by sediments. It can result in the formation of ripples and dunes , in fractal -shaped patterns of erosion, in complex patterns of natural river systems, and in the development of floodplains and the occurrence of flash floods . Sediment moved by water can be larger than sediment moved by air because water has both

1276-879: The initiation of the ice stream (established by looking at velocity data) is caused by a weak bed . Ice streams can also occur in ice fields that are significantly smaller than the Antarctic and Greenland ice sheets. In the Patagonian region of southern South America there are three main icefields - the North Patagonian Icefield, South Patagonian Icefield, and Cordillera Darwin Icefield that all exhibit ice streams. Ice streams are also important for ice sheet dynamics of Iceland's ice fields. In Iceland, areas with reticulated ridges, ribbed moraines , and trunk-flow zones have demonstrated no control over

1320-539: The inside of meander bends. Erosion and deposition can also be regional; erosion can occur due to dam removal and base level fall. Deposition can occur due to dam emplacement that causes the river to pool and deposit its entire load, or due to base level rise. Seas, oceans, and lakes accumulate sediment over time. The sediment can consist of terrigenous material, which originates on land, but may be deposited in either terrestrial, marine, or lacustrine (lake) environments, or of sediments (often biological) originating in

1364-421: The landscape will be altered. Rising sea levels will weather the surrounding sheet and cause erosion and deformation of the sheet itself, thus altering the landscape and morphology. Sediment 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

Norwegian trench - Misplaced Pages Continue

1408-406: The long, intermediate, and short axis lengths of the particle. The form ψ l {\displaystyle \psi _{l}} varies from 1 for a perfectly spherical particle to very small values for a platelike or rodlike particle. An alternate measure was proposed by Sneed and Folk: which, again, varies from 0 to 1 with increasing sphericity. Roundness describes how sharp

1452-632: The main glaciations, the Skagerrak Trough was the meeting point for ice from southeastern Norway, southern Sweden and parts of the Baltic causing a relatively fast-moving ice stream that passed south of the Norwegian coast and then turned north, eventually reaching deepwater at about 62°N. The material carried by the ice stream was then deposited in the North Sea fan. Glacial erratics such as flint and rhomb porphyry , thought to originate from

1496-435: The marine environment include: One other depositional environment which is a mixture of fluvial and marine is the turbidite system, which is a major source of sediment to the deep sedimentary and abyssal basins as well as the deep oceanic trenches . Any depression in a marine environment where sediments accumulate over time is known as a sediment trap . The null point theory explains how sediment deposition undergoes

1540-824: The particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation ; if buried, they may eventually become sandstone and siltstone ( sedimentary rocks ) through lithification . Sediments are most often transported by water ( fluvial processes ), but also wind ( aeolian processes ) and glaciers . Beach sands and river channel deposits are examples of fluvial transport and deposition , though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments. Sediment can be classified based on its grain size , grain shape, and composition. Sediment size

1584-491: The relative input of land (typically fine), marine (typically coarse), and organically-derived (variable with age) sediment. These alterations in marine sediment characterize the amount of sediment suspended in the water column at any given time and sediment-related coral stress. In July 2020, marine biologists reported that aerobic microorganisms (mainly), in " quasi-suspended animation ", were found in organically-poor sediments, up to 101.5 million years old, 250 feet below

1628-473: The removal of native vegetation for the cultivation and harvesting of a single type of crop has left the soil unsupported. Many of these regions are near rivers and drainages. Loss of soil due to erosion removes useful farmland, adds to sediment loads, and can help transport anthropogenic fertilizers into the river system, which leads to eutrophication . The Sediment Delivery Ratio (SDR) is fraction of gross erosion (interill, rill, gully and stream erosion) that

1672-500: The sea a year. The Pine Island and Thwaites streams have the highest amount of net discharge in west Antarctica while Lambert Glacier leads the way in East Antarctica . The rate at which the Antarctic ice sheet is losing mass is accelerating and the past and ongoing acceleration of ice streams and outlet glaciers is considered to be a significant, if not the dominant cause of this recent imbalance. Ice streams hold serious implications for sea level rise as 90% of Antarctica's ice mass

1716-399: The sheet through ice streams, which can be one of many factors causing small stage sheet collapse. In addition to this collapse, ice streams also act to increase the global sea level . As ice streams drain into the surrounding ocean, not only does this increase the sea level due to displacement of the ice runoff, but also by increasing the volumetric content of the oceans themselves, but this

1760-428: The sheet. In Antarctica, the ice streams account for approximately 90% of the sheet's mass loss per year, and approximately 50% of the mass loss in Greenland. The shear forces cause deformation and recrystallization that drive the movement, this movement then causes topographic lows and valleys to form after all of the material in the ice sheet has been discharged. Sediment also plays an important role in flow velocity;

1804-659: The softer and more easily deformed the sediment present, the easier it is for flow velocity to be higher. Most ice streams contain a layer of water at the bottom, which lubricates flow and acts to increase speed. Ice streams are typically found in areas of low topography , surrounded by slower moving, higher topography ice sheets. The low topography arises as a result of various factors, the most prominent being that water accumulates at topographic lows. As water accumulates, its presence increases basal sliding and therefore velocity , which causes an increase in sheet discharge. Another factor causing ice streams to be found in low regions

Norwegian trench - Misplaced Pages Continue

1848-445: The surface of the grain. Form (also called sphericity ) is determined by measuring the size of the particle on its major axes. William C. Krumbein proposed formulas for converting these numbers to a single measure of form, such as where D L {\displaystyle D_{L}} , D I {\displaystyle D_{I}} , and D S {\displaystyle D_{S}} are

1892-494: The use of a scanning electron microscope . Composition of sediment can be measured in terms of: This leads to an ambiguity in which clay can be used as both a size-range and a composition (see clay minerals ). Sediment is transported based on the strength of the flow that carries it and its own size, volume, density, and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, while larger or denser particles will be more likely to fall through

1936-408: The water beneath the ice stream and through the drainage system. These low topographic areas can be up to a few kilometers in depth, and up to hundreds of kilometers in length. The resulting low regions act as a new drainage system for the ice sheet, as it allows movement of material through topographic low to increase, since the stream has left the sheet. Another problem arises from the discharge of

#547452