An ice stream 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 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.
26-502: Tweed River may refer to: River Tweed , on the historic boundary between Scotland and England River Tweed, Leicestershire , England Tweed River (New South Wales) , New South Wales, Australia Tweed River (New Zealand) Tweed River (Western Australia) , a watercourse in Western Australia See also [ edit ] Tweed (disambiguation) Topics referred to by
52-549: A drumlin field . It is the relic of a paleo- ice stream that flowed through the area during the last glaciation. Major towns through which the Tweed flows include Innerleithen , Peebles , Galashiels , Melrose , Kelso , Coldstream and Berwick-upon-Tweed , where it flows into the North Sea . Tweed tributaries include: The upper parts of the catchment of the Tweed in Scotland form
78-475: 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,
104-460: 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
130-514: Is different from Wikidata All article disambiguation pages All disambiguation pages River Tweed The River Tweed , or Tweed Water , Scots : Watter o Tweid , Welsh : Tuedd ), is a river 97 miles (156 km) long that flows east across the Border region in Scotland and northern England. Tweed cloth derives its name from its association with the River Tweed. The Tweed
156-469: 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
182-401: Is expected to be completed during 2028. Ice stream 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; the softer and more easily deformed the sediment present, the easier it
208-587: 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
234-586: 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
260-452: Is one of the great salmon rivers of Britain and the only river in England where an Environment Agency rod licence is not required for angling . The river generates a large income for the local borders region, attracting anglers from all around the world. Tweed may represent an Old Brittonic name meaning "border". A doubtful proposal is that the name is derived from a non-Celtic form of
286-421: 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
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#1732844227029312-484: 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
338-417: 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
364-610: 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
390-574: The Indo-European root *teuha- meaning "swell, grow powerful". The River Tweed flows primarily through the scenic Borders region of Scotland. Eastwards from the settlements on opposing banks of Birgham and Carham it forms the historic boundary between Scotland and England. It rises in the Lowther Hills at Tweed's Well near to where the Clyde , draining northwest (10 kilometres (6.2 mi) from
416-559: 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
442-524: 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,
468-590: The Tweed's Well), and the Annan draining south (1.9 kilometres (1.2 mi) from the Tweed's Well) also rise. "Annan, Tweed and Clyde rise oot the ae hillside" is a saying from the Border region. East of Kelso , it becomes a section of the eastern part of the border. Entering England, its lower reaches are in Northumberland , where it enters the North Sea at Berwick-upon-Tweed . The river east of St Boswells runs through
494-513: The area known as Tweeddale , part of which is protected as the Upper Tweeddale National Scenic Area , one of 40 such areas in Scotland which are defined so as to identify areas of exceptional scenery and to ensure its protection from inappropriate development. Despite that the catchment straddles the border between Scotland and England, management of it – in terms of water quality, bio-security, and ultimately protection of
520-405: 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
546-852: 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
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#1732844227029572-490: The salmon of the River Tweed – is overseen by a single body, the River Tweed Commission. As of 2024 , work is in progress on the development of a 113-mile (182 km) walking and cycling route following the length of the river from Moffat to Berwick-on-Tweed. The work includes new sections of path, upgrades to existing paths, bridge replacement and repairs, pedestrian road crossings, lighting and signage. The path
598-418: The same term [REDACTED] This disambiguation page lists articles associated with the title Tweed River . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Tweed_River&oldid=867396538 " Category : Disambiguation pages Hidden categories: Short description
624-500: 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
650-399: 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
676-408: 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
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