Outwash plain

An outwash plain, also called a sandur (plural: sandurs[1]), sandr[2] or sandar,[3] is a plain formed of glacial sediments deposited by meltwater outwash at the terminus of a glacier. As it flows, the glacier grinds the underlying rock surface and carries the debris along. The meltwater at the snout of the glacier deposits its load of sediment over the outwash plain, with larger boulders being deposited near the terminal moraine, and smaller particles travelling further before being deposited. Sandurs are common in Iceland where geothermal activity accelerates the melting of ice flows and the deposition of sediment by meltwater.

Skeiðarársandur, Iceland
Skeiðarársandur in Iceland, viewed from its eastern margin at the terminus of Svínafellsjökull glacier

Formation

Sandurs are found in glaciated areas, such as Svalbard, Kerguelen Islands, and Iceland. Glaciers and icecaps contain large amounts of silt and sediment, picked up as they erode the underlying rocks when they move slowly downhill, and at the snout of the glacier, meltwater can carry this sediment away from the glacier and deposit it on a broad plain. The material in the outwash plain is often size-sorted by the water runoff of the melting glacier with the finest materials, like silt, being the most distantly re-deposited, whereas larger boulders are the closest to the original terminus of the glacier.

An outwash plain might contain surficial braided stream complexes that rework the original deposits. They may also contain kettle lakes, locations where blocks of ice have melted, leaving a depression that fills with water. The flow pattern of glacial rivers across sandar is typically diffuse and unchannelized, but in situations where the glacial snout has retreated from the terminal moraine, the flow is more channelized.

Sandurs are most common in Iceland, where geothermal activity beneath ice caps speeds up the deposition of sediment by meltwater. As well as regular geothermal activity, volcanic activity gives rise to large glacial bursts several times a century, which carry down large volumes of sediment.

The Gaspé Peninsula that makes up the essential part of southern Quebec (Lower St-Lawrence and Gaspé areas) also contains several example of paleo-sandar, dating from the Pleistocene ice melt.

Lómagnú and Skeiðarárjökull
The western edge of Skeiðarársandur in Iceland shows the diffuse drainage channels typical of sandur.

The prototype sandur

Lómagnú with sand blowing
Unimpeded by topographic obstructions, sand-bearing katabatic winds can be fierce enough on Skeiðarársandur to strip paint from cars.[4] Here, sand is blown in the air in front of the peak Lómagnúpur.

One of the sandurs from which the general name is derived is Skeiðarársandur, a broad sandy wasteland along Iceland's south-eastern coast, between the Vatnajökull icecap and the sea. Volcanic eruptions under the icecap have given rise to many large glacial bursts (jökulhlaups in Icelandic), most recently in 1996, when the Ring Road was washed away (minor floods have also occurred since then). This road, which encircles Iceland and was completed in 1974, has since been repaired. The 1996 jökulhlaup was caused by the eruption of the Grímsvötn volcano, with peak flow estimated to be 50,000 m3/s (1,800,000 cu ft/s) compared to the normal summer peak flow of 200 to 400 m3/s (7,100–14,100 cu ft/s). Net deposition of sediment was estimated to be 12,800,000 m3 (450,000,000 cu ft).

The main braided channels of Skeiðarársandur are the Gígjukvísl and Skeiðará rivers, which incurred net gains of 29 and 24 cm (11.4 and 9.4 in) respectively during the 1996 jökulhlaup. In the Gígjukvísl there was massive sediment deposition of up to 12 m (39 ft), which occurred closest to the terminus of the glacier. The erosional patterns of Skeiðarársandur can be seen by looking at the centimetre-scale elevation differences measured with repeat-pass laser altimetry (LIDAR) flown in 1996 (pre-flood), 1997, and 2001. Of the overall deposition during the 1996 jökulhlaup, nearly half of the net gain had been eroded 4 years after the flood. These two rivers on the sandur display drastically different erosional patterns. The difference in sediment erosion can be attributed to the 2 km (1.2 mi) wide trench near the terminus where the Gígjukvísl flows, in contrast with the Skeiðará, which has braided flows directly onto the outwash plain. The Gígjukvísl river is where some of the highest level of sediment deposit occurred and also where the largest erosion happened afterward. This indicates that these massive jökulhlaup deposits may have a large geomorphic impact in the short term, but the net change on the surface relief could be minimal after a couple years to a decade.

The observed change of Skeiðarársandur from a diffuse to a channelized distributary system where it has the most observed sediment deposit has a significant impact on the development of the fluvial succession in the proximal zone. However, in order to have sustained active accretion across the entire sandur there needs to be a diffuse, multipoint distribution system. The system of accumulation on Skeiðarársandur, which is a product of glacier retreat, can be seen as multiple regions of differing channel patterns that distribute sediment across the plain in dynamic configurations.

See also

References

  1. ^ Ritter, Dale F., R. Craig Kochel, & Jerry Russell Miller. 1995. Process geomorphology. Dubuque, IA: Wm C. Brown, p. 349.
  2. ^ Whittow, John (1984). Dictionary of Physical Geography. London: Penguin, 1984, p. 467. ISBN 0-14-051094-X.
  3. ^ Gornitz, Vivien (ed.). 2009. Encyclopedia of Paleoclimatology And Ancient Environments. Springer: Dordrecht, p. 665.
  4. ^ Leffman, David; Proctor, James (2004). The Rough Guide to Iceland. Rough Guides. p. 28.
  • Church, Michael A. (1972), Baffin Island sandurs: a study of arctic fluvial processes.
  • Garvin J.B. (2001), Topographic Dynamics of Kerguelen Island: A Preliminary SRTM Analysis, American Geophysical Union, Fall Meeting 2001
  • Gomez B., Russell A.J., Finnegan D.C., Smith L.C., Knudsen O. (2001), Sediment Distribution on Skeidararsandur, Southeast Iceland, American Geophysical Union, Fall Meeting 2001
  • Hardardottir J., Snorrason A., Zophoniasson S., Jonsson P., Sigurdsson O., Elefsen S.O. (2003), Glacial Outburst Floods (Jökulhlaups) in Iceland, EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6–11 April 2003
  • Magilligan F.J., Gomez B., Mertes L.A.K., Smith, L.C. Smith N.D., Finnegan D., Garvin J.B., Geomorphic effectiveness, sandur development, and the pattern of landscape response during jökulhlaups: Skeiðarársandur, southeastern Iceland, Geomorphology 44 (2002) 95–113
  • Hétu, B., La déglaciation de la région de Rimouski, Bas-Saint-Laurent (Québec): Indices d'une récurrence glaciaire dans la mer de Goldthwait entre 12400 et 12000 BP, Géographie physique et Quaternaire, 1998, vol. 52, n.3, p. 325-347
  • Smith L.C., Sheng Y., Magilligan F.J., Smith N.D., Gomez B., Mertes L., Krabill W.B., Garven J.B., Geomorphic impact and rapid subsequent recovery from the 1996 Skeiðarársandur jökulhlaup, Iceland, measured with multi-year airborne lidar. Geomorphology vol. 75 Is. 1-2 (2006) 65-75

External links

Coordinates: 61°50′33″N 6°48′28″E / 61.8425°N 6.8078°E

Atlantic Seaboard fall line

The Atlantic Seaboard Fall Line, or Fall Zone, is a 900-mile (1,400 km) escarpment where the Piedmont and Atlantic coastal plain meet in the eastern United States. Much of the Atlantic Seaboard fall line passes through areas where no evidence of faulting is present.

The fall line marks the geologic boundary of hard metamorphosed terrain—the product of the Taconic orogeny—and the sandy, relatively flat outwash plain of the upper continental shelf, formed of unconsolidated Cretaceous and Cenozoic sediments. Examples of Fall Zone features include the Potomac River's Little Falls and the rapids in Richmond, Virginia, where the James River falls across a series of rapids down to its own tidal estuary.

Before navigation improvements such as locks, the fall line was generally the head of navigation on rivers due to their rapids or waterfalls, and the necessary portage around them. Numerous cities initially formed along the fall line because of the availability of water power to operate mills which concentrated mercantile traffic and labor. U.S. Route 1 and later I-95 link many of the fall line cities.

In 1808, Treasury Secretary Albert Gallatin noted the significance of the fall line as an obstacle to improved national communication and commerce between the Atlantic seaboard and the western river systems:

The most prominent, though not perhaps the most insuperable obstacle in the navigation of the Atlantic rivers, consists in their lower falls, which are ascribed to a presumed continuous granite ridge, rising about one hundred and thirty feet above tide water. That ridge from New York to James River inclusively arrests the ascent of the tide; the falls of every river within that space being precisely at the head of the tide; pursuing thence southwardly a direction nearly parallel to the mountains, it recedes from the sea, leaving in each southern river an extent of good navigation between the tide and the falls. Other falls of less magnitude are found at the gaps of the Blue Ridge, through which the rivers have forced their passage...

Au Sable State Forest

The Au Sable State Forest is a state forest in the north-central Lower Peninsula of Michigan. It is operated by the Michigan Department of Natural Resources.The Au Sable State Forest is a byproduct of the lumbering boom in Michigan during the late 19th century. Many parcels of old growth timber were stripped of their largest trees. After forest fires had consumed the resulting detritus, the land had no economic value. Typically, it was sold to subsistence farmers or was reverted to the state in lieu of unpaid property taxes.

Today, the Au Sable State Forest is a valuable asset to the state of Michigan. Much of it surrounds the fast-growing communities of Houghton Lake, Higgins Lake and Lake St. Helen adjacent to Interstate 75. In addition, much of the forest is used for wildlife game management and the fostering of rare and endangered species, such as the Kirtland's warbler. Much of the area sits on the "Grayling outwash plain", a unique habitat.

Baetov

Baetov (Kyrgyz: Баетов, Russian: Баетово, until 1980 Dyurbeldjin) is a village and a center of Ak-Talaa District in Naryn Region of Kyrgyzstan. Its population was 8,354 in 2009. It lies on the Naryn valley road about half-way from Naryn to Kazarman. At this point, a road branches south to Baetov on an outwash plain in the mountains. A jeep road goes south over a 3,268m pass to the At-Bashy valley and A365 to the Torugart Pass.

Black Tern Bog State Natural Area

Black Tern Bog State Natural Area is a Wisconsin Department of Natural Resources-designated State Natural Area featuring 20 acres (8 ha) of quaking sphagnum bog surrounding two small seepage lakes situated in a pitted outwash plain. The bog is rich in plant species, such as sundews, pitcher plant, bogbean, and bog rosemary, as well as three species of bog orchids: swamp pink, grass pink, and rose pogonia. The state-endangered bog rush (Juncus stygius) also grows here. Birds known to nest here include black tern, American bittern, killdeer, and mallards.

Bonab

Bonab (Persian: بناب‎; also Romanized as Bonāb and Benāb; also known as Bināb, Bunab, Binov, and Binev) is a city and capital of Bonab County, East Azerbaijan Province, Iran. It is located west of Maragheh on the outwash plain above Lake Urmia. The people speak Azerbaijani. At the 2006 census, its population was 75,332, in 19,922 families.

Breiðamerkursandur

Breiðamerkursandur is a glacial outwash plain in southeast Iceland. The area is mostly sand, although some vegetation is beginning to grow in the area.

Breiðamerkursandur is located in the municipality of Hornafjörður. It was formed by the glaciers Breiðamerkurjökull, Fjallsjökull and Hrútárjökull during the last few centuries. The lake Jökulsárlón is located on Breiðamerkursandur.

The glaciers that formed the sandur are a part of Vatnajökull, and therefore a part of Vatnajökull National Park. However, neither the plain itself nor the Jökulsárlón lake are a part of the park.Breiðamerkursandur is an important breeding ground for birds, for example Arctic tern and great skua.

Fluvio-glacial

Fluvio refers to things related to rivers and glacial refers to something that is of ice. Fluvio-glacial refers to the meltwater created when a glacier melts. Fluvio-glacial processes can occur on the surface and within the glacier. The deposits that happen within the glacier are revealed after the entire glacier melts or partially retreats. Fluvio-glacial landforms and erosional surfaces include: outwash plains, kames, kame terraces, kettle holes, eskers, varves, and proglacial lakes.

Geest

Geest is a type of landform, slightly raised above the surrounding countryside, that occurs on the plains of Northern Germany, the Northern Netherlands and Denmark. It is a landscape of sandy and gravelly soils formed as a glacial outwash plain and now usually mantled by a heathland vegetation on the glacial deposits left behind after the last ice age during the Pleistocene epoch.The term geest is a substantivisation of the Low German adjective güst, which means "dry and infertile". It is an Old Drift landscape, characterised by the sandy depositions of the Ice Age. In the depressions between the raised flats are wet meadows and, where drainage is poor, bogs. Geest lands are made up of moraines and sandurs. They are almost always next to flat marshlands, the geest being higher and better protected against flood but, compared to the marsh, with poor soil for agriculture. Where the geest borders the sea directly, sand cliffs exist.

The oldest settlements in Northern Germany and Denmark lie on geest, since it provided better protection against storm floods. Many important towns are on the boundary between geest and marshland where people could enjoy the flood-protection of the geest but still use the much more fertile soil in the marsh.

Examples of regions characterised by geest are:

the Burgdorf-Peine Geest

the Cloppenburg Geest near Cloppenburg

the geest hillsides between Wedel, Altona and Hamburg-Neustadt and between Hamburg-St. Georg, Bergedorf, Geesthacht and Lauenburg north of the Elbe (see also: Elbe Urstromtal)

the central geest areas of the islands of Amrum, Föhr and Sylt

the Hanoverian Moor Geest

the Heide-Itzehoe Geest

the Linteln Geest near Kirchlinteln

the Lüneburg Heath in Lower Saxony

the Rehden Geest Moor

the Schleswig Geest

the Stade Geest near Stade (including the Zeven Geest and Wesermünde Geest)

the Wildeshausen Geest in Lower Saxony

the Wingst northwest of Hemmoor (Lower Saxony)

Hjörleifshöfði

Hjörleifshöfði (Icelandic: ['hjœːrˌlifs'hœːfˌði]) is a 221 m (725 ft)-high inselberg in southern Iceland. It consists of palagonite. The mountain is located on the Mýrdalssandur outwash plain about 15 km (9.3 mi) east of Vík í Mýrdal, and was an island in the Atlantic Ocean.

Iroquois County State Wildlife Area

The Iroquois County State Wildlife Area is an Illinois state park that occupies 2,480 acres (1,004 ha) in northeastern Iroquois County, near the border with Indiana. The nearest municipality is Beaverville, Illinois, and the nearest exit on a limited-access highway is Exit 302 on Interstate 57 (Chebanse, Illinois).

Kankakee Outwash Plain

The Kankakee Outwash Plain is a flat plain interspersed with sand dunes in the Kankakee River valley in northwestern Indiana and northeastern Illinois of the United States. It is just south of the Valparaiso Moraine and was formed during the Wisconsin Glaciation. As the glacier, stopped at the Valparaiso Moraine, melted, the meltwater was carried away to the outwash plain. On the south side of the moraine, where the elevation drops, the meltwaters eroded away valleys, carrying sand and mud with them. As the muddy meltwater reached the valley where the slope lessened, the water slowed down, depositing the sand on the outwash plain. This created a smooth, flat, and sandy plain. Before its draining, the Kankakee Marsh, located on the outwash plain, was one of the largest freshwater marshes in the United States.

Kettle (landform)

A kettle (kettle hole, pothole) is a depression/hole in an outwash plain formed by retreating glaciers or draining floodwaters. The kettles are formed as a result of blocks of dead ice left behind by retreating glaciers, which become surrounded by sediment deposited by meltwater streams as there is increased friction. The ice becomes buried in the sediment and when the ice melts, a depression is left called a kettle hole, creating a dimpled appearance on the outwash plain. Lakes often fill these kettles; these are called kettle hole lakes. Another source is the sudden drainage of an ice-dammed lake. When the block melts, the hole it leaves behind is a kettle. As the ice melts, ramparts can form around the edge of the kettle hole. The lakes that fill these holes are seldom more than 10 m (33 ft) deep and eventually become filled with sediment. In acid conditions, a kettle bog may form but in alkaline conditions, it will be kettle peatland.

Mýrdalssandur

Mýrdalssandur (Icelandic: ['mirˌtals'sanˌtur]) is an outwash plain on the south coast of Iceland.

Northwest Indiana

Northwest Indiana comprises Lake, Porter, LaPorte, Newton and Jasper counties in Indiana. This region neighbors Lake Michigan and is part of the Chicago metropolitan area. According to the 2010 Census, Northwest Indiana has a population of 819,537 and is the state's second largest urban area after the Indianapolis Metropolitan Area. It is also the home of the Indiana Dunes, parts of which have been preserved through conservation efforts. The town of Ogden Dunes houses the Hour Glass, a museum showcasing the ecological and conservation efforts of O. D. Frank.The region's largest city is Hammond, followed closely by Gary. Other municipalities in Northwest Indiana include Chesterton, Crown Point, DeMotte, Dyer, East Chicago, Griffith, Highland, Hebron, Hobart, Kentland, Lake Station, La Porte, Merrillville, Michigan City, Munster, Portage, Rensselaer, Schererville, St. John, Cedar Lake, Valparaiso, and Winfield.

Outwash fan

An outwash fan is a fan-shaped body of sediments deposited by braided streams from a melting glacier. Sediment locked within the ice of the glacier, gets transported by the streams of meltwater, and deposits on the outwash plain, at the terminus of the glacier. The outwash, the sediment transported and deposited by the meltwater and that makes up the fan, is usually poorly sorted due to the short distance traveled before being deposited.

Skeiðarársandur

Skeiðarársandur is an Icelandic outwash plain, a vast expanse of sand generated by the transport of debris by the Skeiðará and other rivers, whose flow is generated by the Skeiðarárjökull glacier and fed by the volcanic systems of Grímsvötn and Öræfajökull.

The coastline of the Sandur is 56 km long (from Hvalsík to Hnappavallaós). From Skeiðarárjökull, the valley glacier of Vatnajökull, to the sea is 20-30 km.

The Skeiðará was the most important obstacle in the construction of Iceland's Route 1. It was not until 1974 that it could be completely closed by a 904 m long bridge. This is currently the longest bridge in Iceland. It was temporarily destroyed by water masses and blocks of ice during the last major glacial outburst flood in 1996, triggered by an eruption of the Grímsvötn volcano, but was immediately restored.

The outwash plain originated primarily as alluvial land, i.e. as an accumulation of sediments from the rivers. The sediments deposited here in the Holocene alone range from 100 to 200 km³. However, volcanic eruptions of the volcanic systems of Grímsvötn and Öræfajökull have added to these sediment deposits. The sediments are carried during glacial floods with the glacier water, which thaws during volcanic eruptions, but also through ash deposits.

The outwash plain does not consist entirely of modern sediments. For example, there is also a cliff. In addition, through seismological experiments geologists discovered a 100-150 m deep valley in the bedrock below the modern sediment layers, which was probably milled out by glacial rivers of the Ice Age. Over the last 10,000 years, the outwash plain has grown at a speed of about 1 km³/century.

South Shore, Staten Island

The South Shore is a geographical term applied to the area in the New York City borough of Staten Island, south and east of the island's ridge of hills (and Richmond Creek and Fresh Kills south of Historic Richmond Town) along the waterfront and adjacent areas from the Narrows to the mouth of the Arthur Kill. Many observers prefer to restrict its scope to the neighborhoods located between the shoreline of Raritan Bay on one side and Richmond Creek and Fresh Kills on the other, thus encompassing the neighborhoods of Great Kills to Tottenville only. Those who use this narrower definition of the "South Shore" prefer the term "East Shore" for the communities that lie along Lower New York Bay, and inland for approximately 2 to 2½ miles, from Bay Terrace and Richmondtown to as far north as Grasmere and Concord. The South Shore (under the narrower definition) is represented in the New York City Council by Joe Borelli.

Geologically, the area is an outwash plain of glacial sediment formed from the edge of the terminal moraine, and continues as an underwater shoal into Lower New York Bay, where it was a prime oystering ground in the 19th century.

Prior to the 1960s, the South Shore was undeveloped. After the building of the Verrazzano-Narrows Bridge, the South Shore experienced rapid urbanization and its population rose sharply. The population is predominantly white, but according to census data has been growing more heterogeneous in recent years. Many residents are of Italian, Irish, English, and Jewish descent, with a massive boom to the Italian population in the 1980s and 1990s. The area generally has a low crime rate except for thefts. Truancy, however, is a recurring problem.Commerce was previously dominated by small businesses despite the presence of Hylan Boulevard running along the eastern boundary of the South Shore. However, a number of shopping centers have been built over the last decade. The area is still known for small businesses, including 24-hour delis, pork stores, pizzerias, cafés, gourmet food shops, and a number of independently owned pharmacies, florists, hair, tanning and nail salons, paint stores, and car repair shops.

Vík í Mýrdal

The village of Vík (Icelandic pronunciation: [ˈviːk] (listen); or Vík í Mýrdal in full) is the southernmost village in Iceland, located on the main ring road around the island, around 180 km (110 mi) by road southeast of Reykjavík.

Despite its small size (291 inhabitants as of January 2011) it is the largest settlement for some 70 km (43 mi) around and is an important staging post, and thus it is indicated on road signs from a long distance away. It is an important service center for the inhabitants of and visitors to the coastal strip between Skógar and the west edge of the Mýrdalssandur glacial outwash plain.

Webhannet River

The Webhannet River is an 8.3-mile-long (13.4 km) river whose 8,963-acre (36.27 km2) watershed is contained entirely within the town of Wells, Maine.The river has five tributaries, including three with official names: Pope’s Creek, Depot Brook, and Blacksmith Brook. Draining a sandy outwash plain left by the last glacier, they run parallel to the southern Maine coastline behind the heavily developed barrier beaches of Wells and Drakes Island. The river flows into Wells Harbor, then empties between a pair of jetties into the Gulf of Maine.The Webhannet watershed includes 1,510 acres (6.1 km2) of land under conservation, including 1,167 acres (4.72 km2) of estuary salt marsh and uplands protected by the Rachel Carson National Wildlife Refuge.

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