Arctic, Coastal Geomorphology
The Arctic, long considered a “… region of darkness and mists, where sea, land and sky were merged into a congealed mass” (Nansen 1911, p. 1), has subsequently been defined according to its astronomic, biotic, climatic, cryologic, geomorphic, and hydrologic characteristics (Walker 1983). From the standpoint of coastal morphology, it is the juncture of whichever category is used with the coastline that is important. The determinant that provides the greatest extent to the coastline is sea ice. In the Northern Hemisphere using sea ice as the limiting boundary results in the inclusion of the coastlines of Hudson Bay, Labrador, and Newfoundland, the Sea of Okhotsk and most of the Baltic and Bering Seas (See Ice-Bordered Coasts). By many other criteria, most of these coastlines do not qualify as Arctic.
The Geologic Base
Three large, stable shields composed of Pre-Cambrian rocks form the cornerstones of the Arctic, one each in Canada, Scandinavia, and central Siberia (Fig. 1). The actual exposed lengths of these Pre-Cambrian rocks along the coast is less than what the size of the shields would lead one to believe because their margins have been buried under eroded shield materials. Between and adjacent to the shields, including their buried margins, are folded mountains (or portions of the so-called “mobile belts” of the Northern Hemisphere) some of which extend to the coast (Fig. 1).
Like the embedded coasts surrounding the Atlantic Ocean, Arctic coastal margins are affected by minimal tectonic activity. Earthquakes do occur, as on the north coast of Baffin Island, north of the Mackenzie delta and in the northwest Canadian Archipelago, but they are of low magnitude.
The most recent major event to impact most of the arctic coastal zone is glaciation. The main coastal areas not directly affected by glacial ice during the Pleistocene include the east-central Siberian lowland, a small part of the western Canadian Archipelago and the north coast of Alaska. However, even those coastal zones, though never actually covered by ice sheets, were affected by drainage across them from glacial fronts and by the changes in location of the interface between land and sea due to changes in sea level as the continental glaciers waxed and waned. Today, only a small percentage of the arctic coastline is being modified by glaciers. Major segments are found on Greenland, Ellesmere Island, Novaya Zemblya, and Spitzbergen.
In addition to the direct modifications of the coastlines by glaciers in the form of moraines, drumlins, fiords and strandflats, the rebound that followed deglaciation has (and is) converted formerly submerged coastal belts into subaerial coastal plains. Such occurrences are especially common in northern Canada, the Canadian Archipelago, Scandinavia and the islands north of Siberia. In many locations former coastal features are found today at elevations of as much as 250 m. In the Canadian Archipelago and the Hudson Bay area rebound is continuing at rates of as much as 1 m/century (Andrews 1970).
The Continental Shelf and the Coastal Plain
The two basic contrasting zones of coastal significance in the Arctic are its subaerial and subaqueous portions. These two zones are highly variable in width and in the forms and processes they possess. The continental shelf varies in width from a few kilometers, as off parts of Greenland, to more than 800 km in the East Siberian Sea. With sea-level rise and with coastal erosion, the width of the subaqueous portions of the Arctic Ocean has been increasing. Weber (1989, p. 815), for example, writes that “The Chukchi Shelf was eroded far into the continent and transects the principal mountain ranges of Northern Alaska.” Much of the continental shelf of the Arctic Ocean is flat and shallow, cut only by a few submarine valleys such as those off rivers like the Kolyma and Indigirka and off Barrow, Alaska. Most of the smaller features on the shelves are the result of ice gouging and deltaic deposition or are remnants of subaerial erosion that occurred during lower sea levels (Reimnitz et al. 1988; Weber 1989).
The coastal plain, although not as extensive as the continental shelf, possesses a greater variety of forms and processes than the shelf it borders. Although, the coastal plain of today is subaerial much of it, as in Alaska and northwestern Canada, is the “… landward edge of a continental shelf that has experienced repeated transgressions and withdrawals of the sea …” (Bird 1985, p. 243). It is comprised mainly of gravels, sands, and silts that presently are ice-bonded in the permafrost. In places it is low-lying and level. Near the Indigirka River mouth, for example, storm surges have reached as far as 30 km inland (Zenkovich 1985).
The major forms of the coastal plain that border the ocean include barrier islands and lagoons, sand and gravel beaches, mudflats and marshes, sand dunes, low coastal bluffs, deltas and lengthy rias (gubas in Russian).
Among the arctic coast’s most conspicuous and extensive features are its barrier islands and sandy spits. They are present along much of the coast of arctic Alaska and northwest Canada and along various parts of the Siberian coastline. Some barrier islands are remnants of the coastal plain whereas most are composed of gravel and sand which originated offshore.
Although, most of the deltas in the Arctic are small, they are sufficiently numerous to occupy a sizeable proportion of the coastline. For example, 135 km (or 9%) of the coastline of Alaska between Cape Lisburne and the Canadian border is deltaic (Wiseman et al. 1973).
The deltas of the Arctic, like those elsewhere, are relatively young in that their present-day expression stems only from the time sea-level rise reached a nearly stillstand position about 5000 BP. All of the older deltas in the Arctic contain most of the features, such as distributaries, abandoned channels, lakes, sand bars, mudflats, and sand dunes, that are typical of deltas elsewhere. However, they also possess such cryospheric forms as ice-wedges, ice-wedge polygons, pingos, and thermokarst lakes.
Conditions, Forms and Processes
The present-day appearance of the arctic’s coastline, like that of coastlines elsewhere, depends on modifications that have occurred to the geologic base it inherited. Along many coastlines, these modifications include those engineered by humans. In the case of the Arctic, however, human modifications are still minimal, although they do occur at the mouth of some rivers, adjacent to some coastal villages, and where mining operations, including petroleum exploration and production enterprises, have been developed.
Thus, most of the coastal forms in the Arctic, as is true also of the Antarctic, are the result of natural conditions and processes. Included are those conditions and processes associated with cold climates such as low temperature, snow, ice (river and sea) and permafrost with its many forms of ground ice as well as those of more universal occurrence like relief, structure, sediment type, river discharge, offshore gradient, wave action, currents, storm surges, and tides (Fig. 2).
Cold climate processes are frequently divided into two types: glacial and periglacial (French 1989). Although in the arctic of today glacial processes impact only short lengths of shore, periglacial processes are of major importance along the entire coastline (Harper 1978) including those sections most recently deglaciated.
The sine qua non of periglacial processes is the freezing and thawing of the ground, which is mainly temperature dependent. The change from one state to the other may be daily, seasonal or over longer (thousands of years in some cases) periods of time.
Sub-sea permafrost (offshore permafrost, submarine permafrost) occurs beneath the seabed of the continental shelves of northwest Canada, north Alaska, and Siberia (Fig. 2). It is relic in that it formed when sea level was low and much of the present-day continental shelf was subaerial. It is of major interest today because of its importance to the petroleum industry and as a store of carbon dioxide and methane (Osterkamp 2001).
Sea ice which borders virtually all of the arctic coast during winter, is present along some sections even in summer (Fig. 1). During the time it is shorefast and bottomfast marine action along the coastline is nil. Also, during summer, much of the coastline is protected from wave attack because the presence of sea ice offshore reduces the fetch available to wind and dampens wave action. However, during these periods, often in the Fall of the year when the ice pack has been removed some distance offshore, storm waves may become powerful eroding agents. In 1986, strong winds over the Chukchi and Beaufort Seas resulted in severe erosion of low coastal cliffs impacting heavily the villages of Wainwright and Barrow, Alaska. Other erosive storms also occurred along these coasts in 1954, 1956, and 1963.
Some coastal specialists consider that the passive nature of sea ice is its most important role vis-à-vis the coastline. Nonetheless, sea ice is also an active agent in coastline and offshore modification. Ice push during the periods of freeze up and to a lesser extent during breakup create highly irregular surfaces on arctic beaches. Large pressure ridges formed during freeze up help protect the coastline during breakup because they may last well into the Fall. Although some of the reworked beach forms, including mounds, ridges and kettles, may last for years, depending mainly on how high up on the beach they developed, most tend to be ephemeral because they are removed by summer wave action. Large amounts of beach material (especially sand and gravel but also, in some locations, boulders) can be bulldozed, scoured, rafted, and resuspended by sea ice. In some instances, sea ice rides up on the shore and even overtops low cliffs. If rideup is over a snow bank or an ice foot it will cause minimal modification to the frozen ground beneath.
In addition to the shoreface itself, sea ice causes ice scour out to depths of more than 20 m often several kilometers from the coastline. Deep (2–3 m) gouges or trenches are created by the keels of drifting floes.
Most floes eventually become grounded in which case current movement around them can resuspend bottom sediment and transport it elsewhere.
From the standpoint of the coastline, changes occurring to sea ice because of global warming are likely to be very important in the future. Recent data show that, not only is the ice pack thinning, but its seasonal regimen is changing (Parkinson 2000). If such a trend continues, ice-free periods along coastlines will lengthen and the fetch will increase in length. Thus, both the intensity and duration of waves impacting the shore will also increase.
Impact of Rivers on the Arctic Coast
Four of the ten longest rivers of the world (Ob, Yenisei, Lena and Mackenzie) drain into the Arctic Ocean. In addition, there are numerous smaller rivers, some of which are confined to the zone of continuous permafrost. Many of these smaller rivers cease flow completely during winter. Even the larger rivers are highly seasonal with the major discharge of water and sediment occurring during the snowmelt season (Walker 1998). Thus, the impact of rivers on the coast is confined, like that of most other arctic coastal modifiers, to a few months of the year. Nonetheless, during that restricted season river water impacts the sea ice over and under which it flows.
As sediment-laden floodwater spreads out over the sea ice, its velocity decreases and deposition occurs. Most of the sediment deposited on this bottomfast ice becomes a part of the subaqueous delta as the sea ice melts from under it (Walker 1974). The sediment that is carried by flood-waters beneath the sea ice may be transported many tens of kilometers seaward and become incorporated in long-shore currents and therefore, lost to the deltas.
Ocean Currents, Tides, and Waves
“The Arctic Ocean, relatively isolated in terms of worldwide wind systems and partially or wholly covered with sea ice, depending on season, is a body of water in which low tides, slow-moving currents, and low-energy waves predominate” (Walker 1982, p. 61).
Although there are a few locations in the Arctic where macrotides occur (e.g., off southeast Baffin Island, Canada, and in the Mezen Gulf, Russia, where ranges are more than 10 m), along most of the arctic coast tidal ranges are less than 2 m (Fig. 2). Marshes are often associated with the high tide range locations. Despite low astronomic tidal ranges, storm “tides” occasionally result in deep intrusions of water over low coastal plain surfaces. The inner edge of surge lines are often delineated by the presence of driftwood which is a common contribution of the rivers that flow through the taiga of Asia and North America.
The dominant currents in the Arctic Ocean are the Beaufort Sea Gyre and the Transpolar Drift (Fig. 2). They are the currents that provide the general direction of flow to pack ice and the occasional ice island that breaks off of Greenland and Ellesmere Island. There are other localized currents that affect the coastal zone by transporting sediments along shore and cause sea ice to impinge the coastline. Such ice movements are affected by wind as well as by ocean currents.
Waves, even though their formation is impossible for most of the year because of the canopy of sea ice that covers the ocean, are, nonetheless, the dominant agent in shore modification along most of the arctic coastline. The length of time, waves are effective, varies greatly ranging from several months along the longest-lasting ice-free zones to only occasionally or even rarely along coasts that are often ice-bound even during summer as exampled by parts of the northwest Canadian Archipelago.
Coastal Erosion and Climate Change
Many of the coasts of the Arctic are retreating, some by tens of meters per year especially along some Siberian coastlines (Aré 1988). Along the Beaufort Sea coast of Alaska, erosional rates have been such that since the sea reached its present level 4–5000 BP, the coastline has retreated as much as 25 km (Reimnitz et al. 1988). Rates ranging from 1 to 5 m/a are common in the ice-rich permafrost bluffs bordering much of the Arctic Ocean. In areas north of the Siberian coast, erosion has resulted in the disappearance of some offshore islands.
As most of this retreat is the result of the combined effect of normal marine (wave action) erosion and the periglacial process of thermokarst collapse and thermal erosion, it appears that an increase in the rate of coastal retreat with any rise in sea level and sea-ice degradation is likely.
Such a change would increase the amount of sediment contributed to the shore from cliff erosion which by some calculations already exceeds that contributed by the rivers flowing into the Arctic Ocean (Brown and Solomon 1999). However, it is likely that the same climate changes that affect sea level and sea-ice degradation will also increase permafrost thaw and river discharge and, therefore, the sediment loads of arctic rivers. Whether the relative proportions of the two sources will change is uncertain.
Although a number of localized programs have been undertaken in the last four decades, some of them out of research stations such as the Naval Arctic Research Laboratory, Barrow, Alaska; the Inuvik Research Laboratory, Inuvik, Canada; and the Permafrost Research Institute, Yakutsk, Russia, Arctic coastal research has generally been neglected.
In 1998, at the International Permafrost Conference, a Working Group on Coastal and Offshore Permafrost was formed. This led to the development of an Arctic Coastal Dynamics (ACD) project which has among its objective the establishment of rates of erosion and accumulation, the development of a network of monitoring sites along the coast and the initiation of research on critical coastal processes in the Arctic. The ACD is an international undertaking that bodes well for the future of arctic coastal research.
- Aré F (1988) Thermal abrasion of sea coasts. Polar Geogr Geol 12(1, 2):157Google Scholar
- Are F, Reimnitz E (2000) An overview of the Lena River Delta setting: geology, tectonics, geomorphology, and hydrology. J Coast Res 16(4):1083–1093Google Scholar
- Bird JB (1985) Arctic Canada. In: Bird ECF, Schwartz ML (eds) The world’s coastline. Van Nostand Reinhold Co, New York, pp 241–251Google Scholar
- Brown J, Solomon S (1999) Arctic coastal dynamics. Geological Survey of Canada Open File 3929. Natural Resources, OttawaGoogle Scholar
- de Leffingwell EK (1919) The Canning River region, northern Alaska. United States geological survey professional paper 109. Government Printing Office, Washington, DCGoogle Scholar
- French HM (1989) Cold climate processes. In: Fulton RJ (ed) Quaternary geology of Canada and Greenland, vol K-l. Geological Society of America, Boulder, pp 604–611Google Scholar
- Gusev AI (1952) On the methods of surveying the banks at the mouths of rivers of the Polar Basin. Trans Inst Arct 107:127–128Google Scholar
- Harper JR (1978) The physical processes affecting tundra cliff stability. Unpublished dissertation, Louisiana State University, Baton RougeGoogle Scholar
- Lachenbruch A (1962) Mechanics of thermal contraction cracks and ice-wedge polygons in permafrost. Special publication no. 70. Geological Society of America, New YorkGoogle Scholar
- Nansen F (1911) Northern mists, vol I. Stokes, New YorkGoogle Scholar
- Nielsen N (1985) Greenland. In: Bird ECF, Schwartz ML (eds) The world’s coastline. Van Nostrand Reinhold Co, New York, pp 261–265Google Scholar
- NOAA (1981) United States coast pilot, vol 9. U.S. Department of Commerce, Washington, DCGoogle Scholar
- Osterkamp T (2001) Sub-sea permafrost. In: Encyclopedia of ocean sciences. Academic, San DiegoGoogle Scholar
- Reimnitz E, Graves SM, Barnes PW (1988) Beaufort Sea coastal Erosion, shoreline evolution, and the erosional shelf profile. US Geological Survey Miscellaneous Investigations Series. The Survey, RestonGoogle Scholar
- Sater J, Ronhovde A, Van Allen L (1971) Arctic environment and resources. The Arctic Institute of North America, Washington, DCGoogle Scholar
- Walker HJ (1974) The Colville River and the Beaufort Sea: some interactions. In: Reed JC, Sater JE (eds) The coast and shelf of the Beaufort Sea. The Arctic Institute of North America, Washington, DC, pp 513–540Google Scholar
- Walker HJ (1982) Arctic, coastal morphology. In: Schwartz M (ed) The encyclopedia of beaches and coastal environments. Van Nostrand Reinhold Co, New York, pp 57–61Google Scholar
- Walker HJ (1983) E pluribus unum: small landforms and the Arctic landscape. In: Gardner R, Scoging H (eds) Mega-geomor-phology. Clarendon Press, OxfordGoogle Scholar
- Walker HJ (1998) Arctic deltas. J Coast Res 14(3):718–738Google Scholar
- Wiseman WJ, Coleman JM, Gregory A, Hsu SA, Short AD, Suhayda JN, Walters CD, Wright LD (1973) Alaskan Arctic coastal processes and morphology. Technical report, 149. Coastal Studies Institute, Baton RougeGoogle Scholar
- Zenkovich VP (1985) Arctic USSR. In: Bird ECF, Schwartz ML (eds) The world’s coastline. Van Nostrand Reinhold Co, New York, pp 863–869Google Scholar